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Tripping Curves of Circuit Breakers – B, C, D, K and Z Trip Curve

Types of circuit breaker based on its tripping curve.

A circuit breaker is a protection device employed in every electrical circuit to prevent any potential hazard. There are different types of circuit breakers used all over the world due to their various characteristics & applications. It is necessary to have a circuit breaker that offers adequate protection so that one can work safely around it without having fear of any potential hazards. That is why it is best to know about these kinds of circuit breakers & what kinds of protection do they offer before buying one.

Table of Contents

What is a Circuit Breaker?

A circuit breaker is an electrical device that provides protection against fault current. It breaks the circuit in case of overloading & short circuit. The fault currents generated due to these fault conditions can damage the electrical devices as well as cause fire in a building that can also pose danger to human life.

The circuit breaker instantly cut off the power supply to reduce further damage. A circuit breaker has two types of tripping unit i.e. thermal and magnetic tripping unit.

Thermal Tripping Unit: the thermal tripping unit is used for protection against overloading. It uses a bi-metallic contact that bends with a change in temperature. The current flowing through the bimetallic strip heats up contact & trip the circuit breaker.

The rate of bending of the bi-metallic strip depends on the amount of current. Therefore, greater the overloading current, faster the circuit breaker trips.  

Magnetic Tripping Unit: The magnetic trip unit is used for protection against short circuit current. it includes a solenoid that produced a strong magnetic field due to high short circuit current to instantly trip the circuit breaker.

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• MCB (Miniature Circuit Breaker) – Construction, Working, Types & Applications
• MCCB (Molded Case Circuit Breaker) – Construction, Types & Working

What is a Trip Curve?

A trip curve also known as a current time graph is a graphical representation of the response of a circuit breaker. It shows the current relationship with the tripping time of a protection device.

Why We Need Different Tripping Curves?

Circuit breakers are used for tripping the power supply as quickly as possible in case of overcurrent. But it should not trip so fast & unnecessary that it becomes a problem.

The overcurrent can happen under normal conditions such as the inrush current of a motor. Inrush current is the huge current draw during the starting of a motor that causes voltage dips in the main line. The circuit breaker should be able to tolerate the inrush current & it should provide some delay before tripping.

Therefore, the circuit breaker selected should not trip so fast that it creates a nuisance & it should not trip so late that it causes any damage. This is where the tripping characteristics of the circuit breakers come into play.

The tripping curve tells how fast a circuit breaker will trip at a specific current. The different tripping curves classify the circuit breakers into categories where each category is used for specific types of loads. It is essential to select a circuit breaker that provides the necessary overcurrent protection.

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How to read a Trip Curve?

The following figure shows a chart of a trip curve.

The horizontal X-axis represents the multiples of the current flowing through the circuit breaker. While the Y-axis represents the tripping time of the circuit breaker on a logarithmic scale.

The thermal region shows the response of the bimetallic contact trip unit during overcurrent. The curve shows that the circuit breaker’s tripping time reduces with an increase in the current. The first curve in the graph shows the response of a thermal trip unit.

While the magnetic region shows the response of the solenoid to fault current such as a short circuit current.

As seen from the graph, a circuit breaker does not have a fixed tripping time and we cannot predict an exact tripping point. It is because the tripping is affected by ambient conditions such as temperature. Think of it as a Schrödinger’s Cat area, we do not know when the tripping will occur unless the event happens. 

Types of Circuit Breaker Based on Tripping Curves

The circuit breakers are classified into the following five types based on their tripping curves.

Such type of circuit breaker is designed to instantly trip when the operating current is 3 to 5 times its rated current. Their tripping time falls between 0.04 to 13 seconds. They are suitable for domestic applications where surges are very low such as lighting & resistive loads.

They are sensitive and must not be used in places where the normal surges keep on tripping it unnecessarily.

Type C circuit breaker trips instantly at current surges 5 to 10 times its rated current. its tripping time lies between 0.04 to 5 seconds. As they can tolerate higher surge currents, they are used in commercial applications such as the protection of small motors, transformers, etc.

Type D circuit breaker trips instantly when operating current reaches 10 to 20 times its rated current. Its tripping time is 0.04 to 3 seconds. Such circuit breakers can tolerate the high inrush current of large motors. Therefore, they are suitable for running heavy loads in industrial applications.

Such type of circuit breakers trips at 10 to 12 times its rated current with a tripping time of 0.04 to 5 seconds. These circuit breakers are also used for heavy inductive loads in industrial applications.

Type Z circuit breakers are the most sensitive circuit breaker that instantly trips when the operating current reaches 2 to 3 times its rated current. They are used for sensitive equipment that requires very low short circuit trip settings. 

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This Post has been published by WWW.ELECTRICALTECHNOLOGY.ORG.

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Understanding Miniature Circuit Breaker (MCB) Types and Tripping Curves

• by Bhekusizi Dhlodhlo
• Categories: Blog

Table of Contents

Introduction.

Miniature circuit breakers (MCB) provide protection against short circuits and are rated normally up to 125A. They can be combined with a residual current device, to provide protection against short circuits, overloaded circuits and ground faults.

MCB’s tripping characteristics are represented graphically in a trip curve.  The curve shows the response of the thermal and magnetic trip element to various overload and short circuit situations. 

Those curves are designated letters according to the circuit breaker type. The circuit breaker Types are B, C, D, K and Z corresponding to similar lettered circuit breaker curves.

Why so many different circuit breaker types?

Circuit breaker curves determine the breaker's reaction time to faults. They're the first line of defence against electrical faults. Learn how to select the correct one! 🛡️ #SafetyFirst #ElectricalEngineering #SparkyCalc Tweet

There so many reasons why we need different circuit breaker types with different trip curves and some of the main reasons are:

Selective Coordination

Different electrical components within a system might have varying levels of fault currents they can handle before tripping. 

By using different tripping curves, we can ensure that only the faulty component is disconnected during a fault, allowing the rest of the system to remain operational. 

This selective coordination can be achieved by use of circuit breakers with different tripping curves in a system. We discuss this in more detail in our blog on understanding circuit breaker co-ordination

Equipment Protection

Different types of equipment have different thermal and electromagnetic characteristics. A more sensitive trip curve might be suitable for protecting sensitive electronic equipment, while a less sensitive one may be appropriate for heavy-duty machinery. This ensures that the protection device responds appropriately to the specific needs of the equipment.

Start-Up and Inrush Currents

Some devices such as large motors  experience higher currents during startup or inrush periods. A circuit breaker that allows the flow of high inrush current without tripping can be used in this instance

Fault Types

Different fault types, such as short circuits and overloads, require distinct response times and current thresholds. Circuit breakers with different tripping curves can be used  to address these specific fault conditions appropriately.

Safety and Personnel Protection

Human safety is a critical concern. Tripping curves can be designed to quickly disconnect power in situations where personnel might be at risk, while also preventing unnecessary tripping due to minor fluctuations.

Reading Trip Curves

Reading a Trip curve is not that difficult, give me a sec and I’II explain it to you.

A typical tripping curve is shown above. The horizontal X-axis   represents the multiples of the current flowing through the circuit breaker. While the Y-axis   represents the tripping time of the circuit breaker on a logarithmic scale. A log scale is used so as to fit a wider range of values on the axis.

The top part of the curve is the thermal section of the trip curve’s responds to overloads  which are sustained or long-lasting overcurrent conditions. 

Therefore, a circuit breaker with a thermal trip curve is better suited for high-inrush current applications. The thermal trip curve is typically curved, reflecting the fact that the response time of the circuit breaker increases as the level of overcurrent increases. The thermal trip unit responds relatively slowly yet consistently.

The second part of the curve is the magnetic current section of the trip curve responds to short circuits. It relies on a magnetic coil or solenoid opening when the overcurrent’s design limit is reached. 

The magnetic trip curve is typically a straight line, reflecting the fact that the response time of the circuit breaker is nearly instantaneous for high levels of current.

The bottom part of the time-current curve shows the performance of the instantaneous trip component (short circuit) of the circuit breaker. 

The maximum clearing time (time it takes for breakers to completely open) decreases as current increases. This is because of the blow-apart contact design which utilizes the magnetic field built-up around the contacts.

Breaker types and their trip curves

Now that we’ve learned how to read a trip curve, let’s explore how the type of breaker is linked to these curves and what these curves actually mean.

The first type of circuit breaker that we will look at is the Type B.

Type B circuit breakers have relatively fast tripping characteristics. They are designed to protect sensitive and low-power circuits, such as lighting circuits and some electronic devices. 

The standards state that these breakers trip at 4 times the rated current but MCB’s being mechanical devices are not that exact and will trip anywhere between 3 to 5 times the rated current. The tripping characteristics of this circuit breaker is called a B Curve.

The next one on our list is the Type C circuit breaker.

Type C circuit breakers have medium tripping characteristics. They are commonly used in applications like small motors, small transformers, and general domestic applications where a moderate level of inrush current is expected during normal operation. 

These breakers provide a balance between protecting against overcurrents and allowing for some temporary overloads. The standards state that they should trip at 7.5 times the rated current but will trip anywhere between 5 to 10 times the rated current. The tripping characteristics of this circuit breaker is called a C Curve.

Next we will discuss the Type D circuit breaker.

 Curve D circuit breakers have a delayed tripping characteristic. They are often used in applications with high inrush currents, such as large motors, industrial equipment, and power distribution systems. 

These breakers can handle significant overcurrents for a longer time before tripping, which is suitable for equipment that experiences frequent startup surges. 

The standards state that they should trip at 12.5 times the rated current but will trip anywhere between 10 to 20 times the rated current. The tripping characteristics of this circuit breaker is called a D Curve.

Lets move on to Type K. This circuit breaker is specifically designed for air conditioning and heat pump systems, which often experience high inrush currents during compressor startup. 

Type K provides a delayed response to accommodate these inrush currents while still providing protection against sustained overcurrents. These trip at 8 to 12 times the rated current. The tripping characteristics of this circuit breaker is called a K Curve.

Finally we have Type Z. This circuit breaker is used for specialized applications where the tripping time is extremely fast, even faster than Type A. 

It’s often used in situations where human safety is the primary concern, such as in some elevator systems or medical equipment. This circuit  breaker trips at 2 to 3 times the rated current. The tripping characteristics of this circuit breaker is called a Z Curve.

Rounding Up

I encourage you to reflect on your current or upcoming projects. Are you using the most appropriate type of MCB? Could a different tripping curve offer better protection or efficiency? If you’re unsure, review the technical aspects we’ve discussed, or consult with a professional. 

Your thoughts and experiences are invaluable to this discussion. Please contact me for further discussions. Let’s continue to learn and grow together in our understanding of electrical systems. For more insights, check out similar topics on our blog page and home page . And for updates, don’t forget to subscribe to our newsletter.

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My name is Bheki and I’m an Electrical Engineer. I have a passion for engineering and teaching/mentoring. Qualifications: BEng (Electronic) Hons, MIEAust, CPEng, NER, APEC Engineer IntPE(Aus), RPEQ.

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• Supplemental and Obsolescence Digest 178

Section 7: Miniature and Molded Case Circuit Breakers

• Miniature Circuit Breakers
• Molded Case Circuit Breakers
• Insulated Case Circuit Breakers
• QO Plug-On Circuit Breakers
• Accessories
• QO™ Mounting Bases
• QOU Miniature Circuit Breakers / QYU Supplementary Protectors
• QOU Accessories
• Plug-On Circuit Breakers
• C60 BP and C60 BPR Circuit Breakers
• C60 SP Circuit Breakers
• C60 H-DC Circuit Breakers
• GFP Ground Fault Protectors
• Multi 9 Circuit Breakers Busbar Offer
• C60 Accessories
• PowerPact Family
• B-Frame Circuit Breakers
• H- and J-Frame Circuit Breakers
• Q/LA/LH/Q4-Frame
• PowerPact L-Frame Electronic-Trip Circuit Breakers
• M-Frame Circuit Breakers
• P-Frame Circuit Breakers
• R-Frame Circuit Breakers
• Selective Coordination
• UL Listed 500 Vdc Circuit Breakers
• PowerPact Automatic Switches

Instantaneous Trip Circuit Breakers

• Motor Circuit Protectors and Motor Protector Circuit Breakers
• H-, J-, and LA-Frame MCP Selection
• Electrical Accessories
• Motor Operators and Rotary Handles
• Locks, Installation Accessories, and Rear Connections
• Mechanical Lugs
• Compression Lugs and Power Distribution Connectors (PDC)
• Terminal Nuts, Terminal Pads, Terminal Shields and Accessories
• Plug-In and Drawout Mountings
• PowerPact H-, J-, and L-Frame Trip Units
• PowerPact P- and R-Frame Trip Units
• MicroLogic™ Trip Unit Accessories
• MasterPact™ MTZ Circuit Breakers
• MasterPact™ NT/NW Circuit Breakers
• Enerlin’X System
• Multi-Product Architecture Examples
• Add-On Ground-Fault and Earth-Leakage Modules
• Miniature and Molded Case Circuit Breakers
• Enclosure Accessories and Dimensions

Instantaneous Trip Circuit Breakers for Motor Protection Applications

Adjustable instantaneous-trip circuit breakers are intended for use in combination with motor starters with overload relays for the protection of motor circuits from short circuits.

Other specific applications include rectifiers and resistance welders. These circuit breakers contain a magnetic trip element in each pole with the trip point adjustable from the front. Interrupting ratings are determined by testing the instantaneous-trip circuit breakers in combination with a contactor and overload relay.

Select instantaneous-trip circuit breakers as follows:

This selection table is suitable for motors, other than NEMA Design E, with locked-rotor indicating code letters per NEC ® Table 430.7 (b) as follows:

Locked-Rotor Indicating Codes

For other motors order a special thermal-magnetic circuit breaker with magnetic trip settings for the specific motor— specify motor horsepower, voltage, frequency, full-load current and code letter or locked rotor current.

Determine motor hp rating from the motor nameplate.

Refer to the tables and select an instantaneous-trip circuit breaker with an ampere rating recommended for the hp and voltage involved.

Select an adjustable trip setting of at least 800%, not to exceed 1300%, of the motor full-load amperes (FLA) for other than Design E motors. For Design E motors, select an adjustable trip setting of at least 1100% not to exceed 1700% of FLA.

The NEC 1300% maximum setting may be inadequate for instantaneous-trip circuit breakers to withstand current surges typical of the magnetization current of autotransformer type reduced voltage starters, or open transition wye-delta starters during transfer from “start” to “run,” constant hp multi-speed motors, and motors labeled “high efficiency.” Select thermal-magnetic circuit breakers for those applications.

Part-winding motors, per NEC 430.4, should have two circuit breakers selected from the above at not more than one half the allowable trip setting for the horsepower rating. The two circuit breakers should operate simultaneously as a disconnecting means per NEC 430.103.

Based on NEC 430.52 and NEC Table 430.250.

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Circuit Breaker Tripping: Troubleshooting Guide

Hubert Miles | Licensed Home Inspector, CMI, CPI

Updated on January 5, 2024

A circuit breaker tripping results from short circuits, overloaded circuits, and ground faults. In each case, an unintended excessive flow of current triggers the trip. You must reset the circuit breaker by flipping it back on to restore power.

Circuit breakers trip because they cannot handle the amount of current running through them. Tripping the circuit breaker interrupts the flow of electricity and protects your devices or appliances from damage.

Get FREE estimates from licensed electricians in your area today. Whether you need to replace an outlet, hang a ceiling fan, a new electrical panel, or repair wiring, We Can Help!

Without electrical circuit breakers , the possibility of electrical fires would be much higher.  

This guide looks at what causes circuit breakers to trip, what you can do, and how to identify a bad breaker.

What Would Cause a Circuit Breaker to Trip

There are three leading causes of circuit breaker trips:

• circuit overload
• electrical faults (i.e., ground faults and arc faults)
• short circuits

Below are factors that can cause circuit breaker trips. 

Circuit Overload

A circuit overload happens when the flow of electric current running through the circuit exceeds the amperage of the devices it serves. 

For example, if your microwave is a 12.5 amp appliance, you can run it on a 15 amp circuit. That means your microwave is safe as long as the amperage running through the circuit is 15 amps .

However, if the circuit receives an excessive electrical load over 15 amps , it will automatically trip to protect your device from damage. If the circuit doesn’t trip, the excess current will fry the circuit in your microwave. 

Also, if you operate too many appliances and devices on one circuit, its internal mechanism heats up, causing the breaker to trip. 

Circuit overload is the most common reason for breakers tripping. 

Ground Faults

A ground fault occurs when the active wire comes into contact with a ground wire made of bare copper. Sometimes, this fault may happen when the hot wire touches the metal box connected to the ground wire.

Excessive current flows once the active wire touches the ground wire, flowing into the earth. If you step on the affected area, ground faults can cause shock and even electrocution. The uncontrolled flow of electricity will cause the circuit breaker to trip.

Arc Faults 

An arc fault happens when exposed faulty wiring touches, causing the electric current to arc at the meeting point. As a result, sparks occur, which can ignite an electric fire.

A corroded or loose connection is the main culprit for arc faults. Circuit overloads, ground faults, or short circuits trip an AFCI (Arc Fault Circuit Interrupter) circuit breaker.

Arc faults result from damaged, loose, or corroded terminals and wires. The arc fault builds up over time as the heat due to the cable damage and terminals build up to the point of ignition.

Short Circuits

A short circuit occurs when an active wire touches a neutral wire, and the electrical current takes an unintended path of least resistance. 

The common cause of short circuits is frayed wires coming into contact when the wires touch. The electrical current flow increases significantly, causing the circuit breaker to trip to stop the electricity from damaging appliances.

It is a short circuit because the current bypasses the proper circuit wiring channels and flows through a shorter, unplanned pathway.

Short circuits occur 

• When insulation melts and wires are exposed
• Within appliances with damaged internal wiring
• Due to damaged and frayed extension or appliance cords

How do You Fix a Breaker that Keeps Tripping?

A dedicated circuit breaker tripping indicates too much current flowing through the wiring or connection to the outlet.

Here is a step-by-step guide to follow when you notice the first trip:

• Begin by turning off all the appliances and unplug electrical devices from the outlet. Also, switch off light fixtures and unplug those that you can. This prevents any appliances from damaged when the breaker is reset and a sudden surge of power comes through.
• Open the circuit panel or box and locate the on and off buttons of the circuit breaker. You may notice an orange or red color on the breaker when it is off. 
• Flip the switch from off to on to reset the circuit breaker. Once the breaker is reset, you can switch and test the appliances to see if the electrical power is flowing.
• Keep safe as you reset the breaker by working from the side of the electrical box instead of the front. That way, you will avoid any sparks (should there be any) when you switch the breaker back on.
• Some people prefer to switch the main electrical switch when working on the circuit breaker for added safety. 

Types of Circuit Breakers

Standard circuit breaker.

Standard circuit breakers monitor the modulation of the electric current coming into your devices and appliances. 

This circuit breaker stops the current from flowing when it detects the excessive flow of electricity. 

Standard circuit breakers come in two forms:

• Single-pole circuit breakers
• Double pole circuit breakers

Single-Pole Circuit Breakers

Single-pole circuit breakers are the most common breakers in homes and buildings. They monitor the electric current’s flow in one wire and trip if that wire experiences a very high influx of electricity.

These breakers deliver only 120 volts and work well for 15 to 30 amp circuits. Single-pole circuit breakers come with one switch in the back. 

Double-Pole Circuit Breakers

The double-pole circuit breakers monitor the current in two wires simultaneously. You will notice two switches on the back of these breakers.

The double-pole circuit breakers will trip even if only one of the wires receives too much current. They can accommodate between 15 to 200 amps while delivering 240 volts. 

Single-pole breakers are a good fit for lighting fixtures and other standard home outlets. On the other hand, double-pole breakers work for larger appliances like dryers and washing machines. 

Ground Fault Circuit Interrupter (GFCI)

The GFCI circuit breaker interrupts the line due to ground faults. They trip when the current starts to follow an uncharted path into the ground. These ground fault surges occur when a foreign conductor, like water, comes in contact with a receptacle .

At the same time, they offer protection against circuit overloads and short circuits. 

GFCI circuit breakers come built into specialized outlets required for wet areas in the home, including :

• Outdoor areas like the balcony, patio, porches, and decks
• Laundry rooms
• Swimming pools
• Six feet from a sink
• Six feet from the bathroom

These breakers help prevent shock or electrocution should the electrical outlet contact water. 

Arc Fault Circuit Interrupter (AFCI) 

The AFCI circuit breaker detects normal and abnormal arc faults, so it will trip when it detects a dangerous arc fault that can cause a fire. 

The AFCI circuit breaker doesn’t work to protect devices and appliances plugged into an outlet. It works to prevent electrical fires due to faulty connections and wiring. The internal sensing mechanism in the circuit breaker senses the conditions of an electric arc, and the circuit trips to avoid an electric fire.

AFCI protection can also be built into an outlet. The National Electrical Code (NEC) requires these types of breakers to feature in :

• Common rooms
• Laundry areas

AFCI and GFCI circuit breakers can co-exist and complement each other for the best protection.

Combination All Fault Circuit Interrupter (CAFCI)

The CAFCI breaker senses and reacts to any electrical fault, including ground and arc faults.

CAFCI is a relatively new technology that meets new NEC requirements for circuits requiring arc and ground fault protection.

Do Circuit Breakers Get Weak?

A circuit breaker can wear out and become weak. If a breaker trips frequently, the thermal or magnetic element can lose calibration, causing it to trip at lower amp loads than intended. A breaker constantly under thermal stress caused by overloading the circuit will eventually trip more frequently.

Let’s not forget breakers are not impervious to damage. As the internal mechanical parts wear out, they become very sensitive and may not hold under normal load amperage and temperatures.

Electricians refer to this as a bad breaker .

Will a Bad Breaker Keep Tripping

By definition, bad breaker malfunctions, so it will keep tripping until it is either replaced or rectified .

A licensed electrician performs this simple test to see if a breaker will keep tripping and determine if it can be repaired or replaced in the following steps.

• The electrician will switch off all the fixtures and appliances in the house. Also, unplug everything.
• Find the malfunctioning circuit breaker . The electrician will go to the electrical box and locate the breaker lighting orange or red or the one with the switch off.
• They will ascertain that it is the correct circuit breaker. After that, the electrician puts the breaker off.
• With the switch on, the breaker is back on as well. The electrician will plug the appliances into the outlet with the problem circuit breaker. Now, they will turn the devices and appliances on. 

If the breaker trips, the electrician will investigate the circuit’s current amount. The breaker is bad if the current is according to the appliance’s rating.

How You know if a Circuit Breaker is Bad

Breakers do wear out after a while. It has a problem if the breaker doesn’t stay on after resetting it.

Since the circuit breaker controls the electric flow in the house, it is essential to monitor it and catch signs that it has gone bad early.

Here are key signs that denote a bad circuit breaker :

It Frequently Trips

Frequent tripping could be because of a bad breaker. After tripping and resetting, your circuit breaker should stay on unless it detects high current flow. 

To ensure that the issue is not the electricity but the circuit breaker, call an electrician to examine your electricity’s flow and determine whether it is the cause of the constant tripping.

If it is not, then the circuit breaker is the problem. 

The Breaker Overheats

Electrical systems will heat up when active. Typically a breaker can heat to about 60°C (140°F) before problems arise.

Terminations for standard rated breakers: UL 489 Paragraph 7.1.4.2.2 says the temperature rise on a wiring terminal at a point to which the insulation of a wire is brought up as in actual service shall not exceed 50°C (122°F). Terminations for 100% rated breakers: UL489 Paragraph 7.1.4.3.3 says the temperature rise on the termination shall not exceed 60°C (140°F). Handles, knobs, and other user surfaces: UL489 Paragraph 7.1.4.1.6 says the maximum temperature on handles, knobs, and other surfaces subject to user contact during normal operation shall not exceed 60°C (140°F) on metallic and 85°C (185°F) on nonmetallic surfaces. Source: https://www.clipsal.com/faq/fa173839

Call an electrician immediately if the breaker becomes too hot.

There are Scorch Marks

Scorch marks around receptacles, appliances, and the electrical box should tell you your circuit breaker has gone bad.

The burn marks indicate that wiring insulation has melted off and the circuit wires are now sparking and emanating heat or fire. That means that the circuit breaker did not interrupt the excess current and reached the wires and burned them. 

You may see melted wire sheathing on the wire where it connects to the breaker.

Professional electricians can use a  thermal imaging infrared camera to locate the heat source. The infrared camera allows them to pinpoint the problem area through the walls and other construction material.

A Burning Smell

Sometimes you may smell the insulation burning, but no scorch marks are present to denote which outlet is the problem. 

With the help of the infrared camera, an electrician can help locate electrical issues. 

If you encounter a burning odor, shut off the main power and call for emergency service from an electrician. 

The electrical wires burn because power surges through the circuit, melting the wire insulation.

What is Nuisance Tripping

Nuisance tripping is when a breaker trips without a fault to warrant the interruption to the electric current flow.

Nuisance tripping occurs due to several reasons:

Stringent Protection on Circuits 

Sometimes the circuit is protected by stringent conditions that detect any variance as a fault and cause a trip. 

Such stringent conditions can be tuned to accommodate the home’s or building’s electric needs.

A Highly Sensitive Circuit Breaker

In some cases, the circuit breaker has been set to susceptible settings so that they can detect even the slightest fault, even a minor average variance.

For example, the manufacturer can set an AFCI circuit breaker to sensitive standards to detect another circuit’s arc. This common issue may occur in a daisy chain where the circuit breakers connect in a linear series. There may be a faulty electrical outlet you are unaware of on the circuit. It is common for multiple rooms to share a breaker in older houses.

The Breaker Encounters Power Under Different Conditions

The variation in the current is normal, but the breaker responds to it by tripping because the flow is outside the breaker’s regular operation.

Your circuit breaker is tripping because the voltage it is encountering is not within the standard operation. You will need to adjust the circuit breaker or the voltage to eliminate nuisance tripping.

The Breaker Trips with Nothing Plugged in

A breaker tripping with nothing plugged in occurs when a hot, neutral wire is touching somewhere in the circuit. The common causes include frayed or damaged electrical wires, loose connections, faulty electrical receptacles, light switches , or dimmers.

Electrical wire damage happens when:

• wiring is chewed by animals such as rats, squirrels , raccoons, etc
• wire sheathing and insulation ages and become frayed
• wires rub against sharp edges such as punch-outs with missing grommets or wire clamps

Loose connections often occur when electrical wire nuts come loose or electrical tape wears out causing wires to touch.

Defective wiring can be anywhere along the circuit, so it’s best to contact a licensed electrician to troubleshoot why the breaker is tripping.

Replacing a Bad Circuit Breaker

• Check the electrical panel to see the compatible approved circuit breaker brands. Also, make a note of the brand of the electric panel . This is to help you determine if there are upgrades they could recommend for the hardware.
• Order online or go to the hardware store and purchase the breaker of the same voltage as the one you are replacing.
• Go and open the electrical box and switch off the bad breaker. Loosen the terminals and remove the wires using a pair of needle-nosed pliers. Ensure the pliers have rubber insulated handles to avoid shock or electrocution since you will use the pliers to grab the live wires from the terminal. That is a safety measure.
• Remove the bad breaker. Replace it with the new breaker and slip its clips into place. Remember to switch off the replacement breaker.
• Next, using the pliers, hold the wiring and tighten the screws on the terminal. It is crucial to ensure that the wires and screws in the terminals are in the right place.
• Turn the breaker on and replace the electrical panel cover.

Can a Breaker Fail Without Tipping

If you have a newer electrical panel , it’s not likely for a breaker to fail and not trip. However, in older breaker boxes like Federal Pacific , the breaker failing to trip is common.

The main reason Federal Pacific was investigated by the Consumer Products Safety Commission (CPSC) was widespread structure fires involving breakers failing to trip when an electrical overload was present. They found that the circuit breaker contacts would fuse to the bus bar.

Modern breakers will trip when a failure occurs as an added layer of safety. Most older breakers did not have these safeguards.

With AFCI breakers, if the Internal sensing mechanism fails, the breaker reverts to a standard breaker. The AFCI sensor mechanism will no longer work, but the breaker would still trip from overcurrent protection. Therefore, you should test the AFCI breaker regularly.

Conclusion 

Listen to your circuit breaker . It’s alerting you of a problem when it trips. That communication could be a problem with the breaker itself, the circuit, or the amount of electric current coming into your home.

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.

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What Causes Circuit Breakers To Trip?

• April 2, 2024

If your circuit breakers keep tripping, there’s no need to stress. This is a typical situation. Below, you’ll find details on the reasons behind this and tips for avoiding it going forward. Get a handle on your circuit breaker issues!

Table of Contents

Understanding Circuit Breaker Tripping

Circuit breakers are protection devices for electrical circuits. When too much current passes, the breaker trips, stopping the flow of electricity and preventing damage. This can be caused by faulty wiring, too many appliances on one circuit, or a ground fault.

Overloading can cause tripping. This happens when too many devices are connected to a single circuit. Heat builds up in the wires, which can start fires or cause damage. To prevent this, distribute loads across multiple circuits and don’t connect too many appliances to one outlet.

Short circuits also lead to tripping. This happens when two wires with opposite charges come in contact or when a wire touches something grounded. This causes an immediate surge in current that triggers the breaker. Check for exposed wires or insulation damage, and call an electrician if you spot any signs of trouble.

Ground faults can also cause tripping. This happens when there’s an unintentional connection between a live wire and a conductive surface. Install GFCIs to avoid this.

In short, know what causes circuit breakers to trip. Identify potential hazards like overloading, short circuits, and ground faults. Take steps to prevent accidents and ensure your electrical equipment is safe. If you’re unsure how to handle electrical problems, call a licensed electrician.

Overloading Causes

Circuit breakers trip to stop overheating, electrical fires, and damage to electrical parts. Plugging in too many devices can cause the circuit to become overloaded, so the breaker trips to cut off the power.

Short circuits are like a blind date gone wrong. They can be explosive, and often end in disaster. This happens when a hot wire comes into contact with a neutral or insulation/water. This throws off the electric balance, causing danger and tripping.

Short Circuit Causes

A short circuit happens when a low-resistance path appears between two points in the circuit that aren’t usually connected. This can cause too much current to flow, making a circuit breaker trip. Insulation or wiring damage, faulty appliances, and circuit overload are the most common reasons for a short circuit. It’s critical to identify and fix the root cause quickly to avoid electrical fires and other dangers .

When too much power passes through a circuit, the circuit breaker will automatically turn off. It’s designed to protect wiring and guard against electrical accidents . But if the breaker trips regularly, there may be underlying issues that need investigation and repair. Often times, this means upgrading or replacing components.

Sometimes short circuits are caused by human error or wear and tear. But they may also come from design or installation problems. Planning and upkeep from local electricians can keep electrical systems running safely and appropriately for a long time. If your circuit breaker is tripping a lot, get an experienced technician to review your system and suggest solutions that match your needs and budget .

Overheating Causes

Circuit breakers are essential safety features. They stop electrical fires and protect your appliances. When overloaded, too much current flows, producing heat. This causes the breaker to trip!

Other factors can cause overheating. Damaged insulation on wires increases resistance. Loose connections add resistance and heat. High temperatures and poor ventilation worsen the situation.

It’s important to maintain and service the electrical system. Checks of all components will make sure they work efficiently. To avoid tripping, prevent overheating. This will reduce energy consumption and safeguard equipment. So, let’s learn about circuit breakers and how they deal with overloads!

Circuit Breaker Types

Circuit breakers are essential for any electrical system. They prevent overloaded and faulted circuits . There are different types of circuit breakers suitable for specific electrical loads.

See the table below for the different types of circuit breakers and their functions:

It is crucial to select the right type of breaker. Each one has its own advantages in specific situations. For instance, thermal circuit breakers are perfect for small appliances like hair dryers or irons . Meanwhile, magnetic circuit breakers are great for bigger loads such as air conditioners or refrigerators .

Remember, circuit breakers are like Beyoncé – they can handle a lot, but have their limits.

Circuit Breaker Ratings and Specifications

Circuit breakers are designed to protect electrical circuits from overloads. To ensure that circuits and appliances are safe, the ratings and specifications of circuit breakers need to be understood.

If a circuit breaker trips often, it may mean there’s an issue. It’s best to get professional help in these cases. Time to go on a hunt for your electrical wiring!

Troubleshooting Circuit Breaker Tripping

Circuit breakers can flip out for multiple reasons, like overloads , short circuits , and ground faults .

Overloads happen when too much electricity passes through the circuit, creating too much heat and tripping the breaker. Short circuits are when two or more wires touch, resulting in extra current. Ground faults occur when the power takes an unexpected route, like through a person’s body.

To figure out why your circuit breaker is tripping, it’s important to figure out what is going on and act accordingly. Inspections and maintenance can also help avoid future tripping.

Stop your circuit breaker from misbehaving with these prevention tips!

Preventing Circuit Breaker Tripping

A circuit breaker tripping can be prevented with understanding. When circuits are overloaded, breakers trip to avoid overheating and potential fires. Here are 3 steps that can help you prevent circuit breakers tripping:

• Know the electrical load – work out how many appliances & devices are connected to one circuit. Don’t overload them by spreading high-energy equipment across multiple circuits .
• Look after your appliances – ensure all your appliances & devices are in good condition, with no damaged cords or frayed wires.
• Upgrade your system – if you’re tripping breakers often you may need to upgrade the electrical system with higher capacity breakers or more circuits.

Plus, investing in surge protectors can also assist in preventing circuit overload and subsequent tripping of breakers. By following these steps you can make sure your home’s electricity runs safely and without interruption due to circuit breakers tripping.

Remember: these precautions will keep you from tripping more than just your circuit breakers!

Safety Precautions

Safety must be taken seriously when dealing with circuit breakers . Always switch off the main power supply before beginning work. Wear protective gear such as insulated gloves and boots to stay safe from electrocution. Never touch wires or components inside the box without proper training. Keep the area around the breaker box free from any flammable substances. Inspect breakers for damage or wear regularly .

Label each circuit breaker correctly . Test them frequently for functionality. This will help identify circuits quickly in case of an emergency. These precautions and practices ensure safety while dealing with circuit breakers. When in doubt, blame it on the circuit breaker – it’s always a good scapegoat for electrical woes!

Circuit breakers are essential components of any electrical system. They stop too much current flowing and thus, protect against potential fires . The most common cause for tripping is overload. But, other causes like short circuits and ground faults can also cause the breaker to trip. When it trips, there is something wrong that needs to be fixed right away.

Short circuits occur when two wires touch each other. This creates a low resistance path which allows a lot of current to flow with no load. Ground faults occur when the hot wire touches something incorrectly wired or with a damaged cord.

To prevent tripping, regular maintenance of the electrical system is needed. Keeping appliances in good condition, replacing worn-out cords and fixtures, and periodically checking for loose wires all help reduce the chances of tripping. In summary, understanding why the breaker trips and taking precautionary measures will keep you safe and save you repair costs.

Frequently Asked Questions

1. what causes a circuit breaker to trip.

There are several possible causes, including overheating due to circuit overload, short circuits, ground faults, and age-related wear and tear.

2. How can I prevent my circuit breaker from tripping?

You can avoid overloading your circuit by keeping the number of electrical appliances used on one circuit to a minimum, regularly checking wires for signs of wear and tear, and not using too many extension cords.

3. What should I do if my circuit breaker keeps tripping?

If your circuit breaker is constantly tripping, it is important to identify and fix the underlying issue. Contact an electrician to inspect and repair any faulty wiring or electrical devices.

4. Can a circuit breaker trip without an overload?

Yes, a circuit breaker can trip due to a short circuit or a ground fault, which may occur without an overload.

5. How do I reset a tripped circuit breaker?

To reset a tripped circuit breaker, turn it off and then back on again. Make sure to identify and correct the underlying issue that caused the trip before restoring power.

6. What is the lifespan of a circuit breaker?

The lifespan of a circuit breaker can vary depending on usage and other factors. However, most circuit breakers last between 10 and 30 years.

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Why Is My Circuit Breaker Tripping? 4 Potential Problems and Solutions

By: Glenda Taylor , Bob Vila , Evelyn Auer

Updated on Dec 21, 2023 8:55 PM EST

6 minute read

Photo: istockphoto.com

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Q: Every few hours—sometimes minutes!—my living room and one side of my kitchen lose electrical power. I’ll check the breaker panel and, sure enough, a circuit breaker has tripped…again. Should I call an electrician, or is there a simple DIY fix I can try first?

A: While it’s frustrating when a circuit breaker keeps tripping, they are important safety mechanisms. Designed to shut off the electrical current when something goes wrong, circuit breakers are one of the best ways of protecting a home from an electrical fire. “When a circuit breaker trips, typically it is because we use too much electricity, which causes it to overload and turn off,” says Christopher Haas, expert electrician and owner of Haas & Sons Electric in Millersville, Maryland. For those who need an electrical panels 101 refresher course or aren’t sure how to reset circuit breakers, each breaker has an on/off switch and controls a separate electrical circuit in the home. When a breaker trips, its switch automatically flips “off,” and it must be manually turned back on to restore electricity to the circuit. For those wondering, “Is it dangerous if a circuit breaker keeps tripping?” the answer is that it can be, depending on the source of the problem. An electrician can ultimately deal with the root issue, but a little sleuthing will reveal whether it’s something that’s easily remedied.

In many cases, the cause of a circuit breaking tripping is an overloaded circuit.

A circuit overloads when more electrical current is being drawn through the wires than they can handle, tripping the circuit breaker. If this happens, there may be a few additional signs:

• Buzzing noises coming from outlets
• Devices charging slowly
• Electrical outlets not working
• Flickering lights
• Scorch marks on outlets and light switches

If a circuit breaker keeps tripping in one room, homeowners can test for circuit overload by turning off all the switches in the affected area and unplugging all appliances and devices. After the breaker is flipped back on, the devices can be turned back on one at a time, with homeowners waiting a few minutes in between to see if the circuit remains on. If the breaker trips before all the appliances are turned on, the experiment can be repeated, this time turning them on in a different order. It may be necessary to do this several times to find out how many appliances can be operated at once before the circuit overloads.

“As a short-term solution, you can unplug unnecessary appliances to prevent tripping circuit breakers. You may still get some trips, but you can limit them by unplugging devices that you don’t need to use,” advises Dan Mock, vice president of operations at Mister Sparky , an electrical company with 90 locations in the U.S. The best long-term solution, however, is to pay an electrician for the cost to rewire the house and add additional circuits. The cost to replace an electrical panel is about $1,274 on average.

Other times, the issue may be caused by a short circuit.

A “short” circuit means that two wires that should not be coming into contact are inadvertently touching, triggering a sudden surge of electricity through the wires. A short can occur in an outlet, a switch, or within an appliance if wires are loose or have been chewed through by mice or pets. Some signs of a short circuit include:

• Popping sounds
• Discolored outlets or switches
• Burning smells

Testing to see if an appliance has a short is similar to testing for an overloaded circuit. When an appliance that has a short in its wiring is turned on, it will immediately trip the circuit. Homeowners can also try plugging it into an outlet in a different room. If the breaker for that room trips, there’s a short in the appliance (if it’s unclear what breaker goes to what room, the breaker can be identified with one of the best circuit breaker finders ). Electrical shorts can be a major fire hazard, so it’s a good idea to call a licensed electrician for this circuit breaker repair. It’s wise to stop using the outlet or appliance until a pro takes care of the problem.

Another potential cause of a circuit breaker tripping is a ground fault.

A ground fault occurs when the electricity running through a home’s wiring diverts from the wiring loop and travels to the ground, usually due to faulty wiring or water infiltration in an outlet or switch box. Water is a conductor, which is why walking through puddles is often listed as something not to do in a power outage in case of downed power lines. Once water makes contact with wires, electricity can jump from the wiring loop and follow the water trail. This creates a surge in electricity leading to a tripped circuit breaker. If a person comes in contact with the electricity that is on its way to the ground, this can result in electrocution. Homeowners may notice a few signs of a ground fault, including:

• Tripped GFCI (ground fault circuit interrupter) outlets;
• A burning smell coming from an outlet; and
• Lights flickering.

Newer electrical breakers have features designed to protect against the danger of ground faults. According to Haas, “Ground fault breakers sense electricity going to earth as opposed to going through the wires of the circuit. You’ll find [these] for bathrooms, kitchens, garages, exteriors, and basements.” GFCI outlets are another safety feature that shut off the electric current within a fraction of a second of sensing a ground fault.

If a ground fault is the problem, the cause of the errant water must be discovered and repaired, and any damaged wiring must also be replaced. It’s also a good idea to install GFCI outlets in rooms where water is commonly used. A GFCI outlet costs $210 on average.

Sometimes a bad or worn-out circuit breaker can be the culprit.

In some cases, the circuit breaker itself may be faulty. Breakers that are old, damaged, or were installed incorrectly may trip frequently for no apparent reason. Alternatively, faulty breakers may not trip when they are supposed to, leaving the home at risk of electrical fire. Some signs of a bad circuit breaker include:

• The circuit breaker getting hot and tripping frequently;
• The circuit breaker won’t reset;
• It has been over 10 years since the breaker was last serviced; and
• The breaker has scorch marks.

An important electrical safety tip to keep in mind is that resetting a breaker over and over again can cause what is called an arc flash, which is a small electrical explosion that can be deadly. If resetting the breaker once does not remedy the issue, it’s a good idea for the homeowner to hire an electrician near them who knows how to replace a circuit breaker safely. Mock warns, “Don’t take any chances with circuit breakers. Instead, call a licensed electrician who knows the safe ways to replace breaker boxes, upgrade circuits, and diagnose potential electrical problems in your home.” Wiring a breaker box is a job to leave to an experienced electrician.

A professional electrician can help determine the specific cause of a frequently tripping circuit breaker.

Most circuit breaker problems—aside from those explained in the sections above—will need to be inspected and addressed by a licensed electrician. According to the Electrical Safety Foundation International (ESFI) , each year “thousands of people in the United States are critically injured and electrocuted as a result of electrical fires, accidents, [or] electrocution in their own homes.” While homeowners may be tempted to save on electrician costs by attempting circuit breaker replacement or repair themselves, electrical work is not suitable for casual DIYers. “Yes, you have to pay, but you can save many hours of head-scratching by hiring an electrician. Electricians will also have all the right tools for diagnosing and repairing the circuit,” Haas adds. “Lastly, they will come with a warranty/guarantee should something arise, and they will typically return at no additional cost.”

The Government Is Paying People to Upgrade Their Home Comfort, Here’s Why The Government Is Paying People to Upgrade Their Home Comfort, Here’s Why

By: Tony Carrick

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General | QUICK-TRIP AC-PRO-II | QUICK-TRIP For AC-PRO | Installation

The QUICK-TRIP ® system is a manually controlled arc flash reduction system. It can reduce trip times when turned on and allows selective coordination between circuit breakers when turned off. If maintenance personal must work on energized equipment, they will first turn the QUICK-TRIP ® system on at the breaker feeding the equipment. If a fault occurs, the upstream breaker will trip quickly based on the QUICK-TRIP ® settings reducing the arc flash hazard to personnel.

The QUICK–TRIP ® settings are separate ground fault (QT GF) and instantaneous (QT I) settings in the AC–PRO ® and AC–PRO–II ® .  The QT GF & QT I have the same ranges as the regular GF and I settings in the AC-PRO ® and AC-PRO-II ® . The settings are dormant until the QUICK–TRIP ® switch is turned ON. When the switch is turned back OFF the AC–PRO ® and AC–PRO–II ® returns to its original settings.

Example: A feeder breaker needs to be racked out for maintenance. Before opening the cubicle, QUICK–TRIP ® would be activated on the main. If an incident occurs during the racking out, the main would trip on the QT GF or QT I instead of the standard settings. Since the main tripped faster than usual, the amount of energy build up would be less and the arc flash would be reduced.

A reduction in arc flash incident energy levels may permit lower PPE clothing for maintenance personal.

All QUICK-TRIP ® Switches are pad-lockable.

Remote QUICK-TRIP ® control and indication is also possible. Contact us for additional information.

QUICK-TRIP ® for AC-PRO-II ®

For AC-PRO-II ® Trip Units, two (2) QUICK-TRIP ® options are available:

Option 1: Configuration using the QT-DISPLAY-IM ® , the QT-Display ® , and the QT-Switch ®

• View trip unit info without opening the cubicle door
• Lockable QT-Switch ® for Arc Flash Reduction
• QUICK-TRIP ® ON LED, Self-Test LED, Pickup LED, 1x16 Character LCD, Review Button
• Allows the QT-DISPLAY ® and QT-Switch ® to be used with either AC-PRO-II ® or AC-PRO ® .
• Allows QT-DISPLAY ® to display Currents, Voltages*, Power*, Energy*, Settings, and Last Trip Data from AC-PRO-II ® (*requires VDM for Voltage, Power and Energy data).
• Includes USB extension port for AC-PRO-II ® (For InfoPro-AC ® software and SAFE-T-TRIP ® ).
• Requires control power. Versatile design accepts 120VAC, 125VDC, or 24VDC.
• Compatable with Existing Products
• Cubicles where QT-DISPLAY ® is already installed.
• Cubicles where breakers with either AC-PRO-II ® or AC-PRO ® could be racked in.

Option 2: Configuration using the QT2-Switch ® & AC-PRO-II ®

• Integral QUICK-TRIP ® Switch (lockable) and QUICK-TRIP ® LED
• Terminals for Remote QUICK-TRIP ® Switch wiring and remote QUICK-TRIP ® indication wiring
• “Push-to-Verify” Button (for verification of QUICK-TRIP ® status on battery power)

Click here for a practical example of how QUICK-TRIP ® can be used to lower incident energy,

QUICK TRIP ® for AC-PRO ®

The QUICK-TRIP ® system for AC-PRO ® comes with the QT-Display ® , QT-Switch ® with a padlockable cover and all the necessary mounting hardware and cables. The QT-Display is a read only device that extends the use of the AC-PRO ® to a more convenient and safe location for personnel to view the continuously displayed 3-phase current, the "PICK-UP" LED, "Self-Test" LED and review last trip data and unit settings. All of this can be done without opening the cubicle door.  

QT-Display ® and QT-Switch ® Features

Click here for a practical example of how QUICK-TRIP ® can be used to lower incident energy.

Installation

• Equipment is mounted to the cubicle door
• Simple cable connections to trip unit
• See AC-PRO ® Installation Manual for QT-Display ® installation info
• See AC-PRO-II ® Installation Manual for QT2-Switch ® installation info
• See QT-DISPLAY-IM ® Installation Manual for its installation info

Informational video installation guide of the QT-2 Switch ® for AC-PRO-II ®

Product Information

QT-Display-IM ® Instruction Manual v1.0

AC-PRO-II ® Instruction Manual

AC-PRO ® Instruction Manual

Data Sheets

QUICK-TRIP ® for AC-PRO ® Product Flier

QUICK-TRIP ® For AC-PRO-II ® Product Flier

QUICK-TRIP ® with Kirk Key

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Quick trip transformer breakers

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Are the new electronic or fast trip circut breakers worth installig on ZW and KW transformers or just use externa or both. Already know to use TVS diodes.  

A circuit breaker of any speed and the TVS protection diodes serve entirely different functions. Circuit breakers react to current overloads on the circuit, the TVS diode suppresses transient EMI spikes. Even if you have the worlds best circuit breaker, the TVS protection diode is still a good idea.  

I did a post a couple or more years ago on this. Posted manufacturer's curves showing how long it would take a "fast trip" breaker to open, and how far above the posted rating you had to go to get anywhere near close to a almost instantaneous trip (something like 4-5 times the rated trip). It's why I choose to use fuses and why you find fuses on the MTH DCS boxes. AND I put TVS diodes for the reason GRJ mentioned. I have a breaker on the transformer supply power, but not on the track power.  

Quietman said: I did a post a couple or more years ago on this. Posted manufacturer's curves showing how long it would take a "fast trip" breaker to open, and how far above the posted rating you had to go to get anywhere near close to a almost instantaneous trip (something like 4-5 times the rated trip). It's why I choose to use fuses and why you find fuses on the MTH DCS boxes. AND I put TVS diodes for the reason GRJ mentioned. I have a breaker on the transformer supply power, but not on the track power. Click to expand...

Scroll down to page 67 of this Airpax product brochure. The second number grouping is the delay. I got Airpax push-pull type at Digikey a few years ago, but made the mistake of getting a delay of 2. I don’t see any of that type with a 0 delay at Digikey at the moment. ourproducts_snapak_series_datasheet.pdf (sensata.com) Looks like the Eaton FAZ-B breakers are available at automationdirect. They are harder to mount (you need a DIN rail), but cost less. Here is the Eaton spec sheet. Eaton FAZ Series Supplementary Protectors (automationdirect.com) I got FAZ-B5/1-SP and they work well. I also got some 3 and 4 amp FAZs as you can see in the above photo and they also work well.  

Lehigh74 said: Scroll down to page 67 of this Airpax product brochure. The second number grouping is the delay. I got Airpax push-pull type at Digikey a few years ago, but made the mistake of getting a delay of 2. I don’t see any of that type with a 0 delay at Digikey at the moment. ourproducts_snapak_series_datasheet.pdf (sensata.com) Click to expand...

GRJ and Bob. Thanks for the info on the Airpax. Put one inline while I was testing the new wiring on the Christmas layout. At that point I hadn't hooked up the DCS system yet, but just had a transformer and a conventional loco. Had a minor derailment - only one truck, and it tripped so fast I thought at first I'd missed when it derailed and only realized I had an issue when it tripped. Turned the knob to 0V, reset the breaker, and as soon as voltage was applied it tripped. As you guys said, just like a fuse. I know it was immediate, instead of waiting to reach a certain voltage, as there was an analog voltage meter on the power to the track. As soon as the needle tried to move, the breaker tripped. Had been looking for something like that. Wonderful tip from you guys.  

Stoshu said: Have you looked at the Lionel 6-34120 TMCC direct lock on ? very fast and also has LED indicator lights on it. With 2 grand kids it saved a lot of trains. Click to expand...

I agree with the DCS part John. My signals went from a 10 to 7, but everything still works on my layout. It might be a issue on a large layout.  

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