How to Choose a Circuit Breaker

There are a few different criteria to consider when selecting a circuit breaker including voltage, frequency, interrupting capacity, continuous current rating, unusual operating conditions and product testing. This article will give a step by step overview on selecting an appropriate circuit breaker for your specific application.

Voltage Rating

Circuit Breakers Available in Different Sizes & ConfigurationsThe overall voltage rating is calculated by the highest voltage that can be applied across all end ports, the distribution type and how the circuit breaker is directly integrated into the system. It is important to select a circuit breaker with enough voltage capacity to meet the end application


Circuit breakers up to 600 amps can be applied to frequencies of 50-120 Hz. Higher than 120 Hz frequencies will end up with the breaker having to derate. During higher frequency projects, the eddy currents and iron losses causes greater heating within the thermal trip components thus requiring the breaker to be derated or specifically calibrated. The total quantity of deration depends on the ampere rating, frame size as well as the current frequency. A general rule of thumb is the higher the ampere rating in a specific frame size the greater the derating needed

Maximum Interrupting Capacity

The interrupting rating is generally accepted as the highest amount of fault current the breaker Control Panel Circuit Breakerscan interrupt without causing system failure to itself. Determining the maximum amount of fault current supplied by a system can be calculated at any given time. The one infallible rule that must be followed when applying the correct circuit breaker is that the interrupting capacity of the breaker must be equal or greater than the amount of fault current that can be delivered at the point in the system where the breaker is applied. Failure to apply the correct amount of interrupting capacity will result in damage to the breaker.

Continuous Current Rating

In regards to continuous current rating, molded case circuit breakers are rated in amperes at a specific ambient temperature. This ampere rating is the continuous current the breaker will carry in the ambient temperature where it was calibrated. A general rule of thumb for circuit breaker manufactures is to calibrate their standard breakers at 104° F


How to Choose the Right Circuit Breaker

Circuit breakers are a very important part of electrical safety. They control the amount of electricity that flows through a building’s electrical wiring system. If your home suffers an electric overload or a short circuit, a properly functioning circuit breaker will detect the issue and cut off the electrical supply. This will protect your wiring and appliances until you take care of the problem and restart the electricity. However, in order for a circuit breaker to do its job properly, you have to match the right circuit breaker with your exact needs. Read the following simple explanations and you’ll be ready to choose the appropriate circuit breaker for your home.

Low-voltage thermal magnetic circuit breakers are best suited for most single-family homes. They allow for electrical currents that measure only up to 1000 amps

Medium voltage circuit breakers are used in larger buildings, such as apartment complexes and businesses, that use up to 72,000 volts on a regular basis

High-voltage circuit breakers are used alongside power lines and in other places that use more than 72,000 volts regularly.

Figure Out the Breaker Size You Need

In order to choose the best-size circuit breaker for your particular household needs, check the wire size printed on the cable that is to be connected to the circuit breaker. You will see 2 measurements listed: The first will tell you the wire gauge, followed by a dash and a second number which indicates how many wires are inside the cable. Once you have established the wire gauge


How to Test a Circuit Breaker

Circuit Breaker Tester: Clamping Ammeter

Circuit breakers that trip every time they’re reset may be overloaded. In order to diagnose a circuit breaker overload you can test the circuit breaker by using a clamping ammeter. This circuit breaker tester is used to check overloads and shorts that are in progress and determine whether the electric current is running through the circuit. The clamping ammeter should be clamped to a single wire not the cable in order to accurately test the circuit breaker.

Circuit Breaker Tester: Electromagnetic Circuit Finder (Current Tracer)

Circuit breakers may trip and disconnect all electricity, but sometimes that is not the case. An electromagnetic circuit finder will test to see if the circuit breaker has a live connection. It will determine which individual breaker controls a live circuit.

Circuit Breaker Tester: Electrostatic Wand

Circuit breaker testing can be helpful if you are trying to determine the flow of electricity in the circuit breaker panel. A circuit breaker Need link should be tested even if you have turned it off; it is important to make sure the wires are dead and there is no current flowing in them

Circuit Breaker Tester: Multimeter

The multimeter circuit breaker tester combines the characteristics of a voltmeter and the ohmmeter in one. This multipurpose circuit breaker testing device has multiple functions. Like the voltmeter it measures the level of voltage in the circuit and also measures the continuity and resistance level (ohmmeter). Obtaining information about both electrical readings can help pinpoint circuit breaker problems quickly and accurately so that repairs can be made.

Circuit Breaker Tester: Voltmeter

Circuit breaker testing can get complicated when using small inexpensive testers. A voltmeter is a popular circuit breaker testing tool used by homeowners. This circuit breaker tester measures the voltage running through the electrical circuit. The voltmeter is used by touching one prong to each of the parts of a circuit between which you need to measure voltage. For example, you would touch one prong to the neutral wire and the other to the hot wire to measure the voltage in a circuit


How Circuit Breakers Work

The circuit breaker is an absolutely essential device in the modern world, and one of the most important safety mechanisms in your home. Whenever electrical wiring in a building has too much current flowing through it, these simple machines cut the power until somebody can fix the problem. Without circuit breakers (or the alternative, fuses), household electricity would be impractical because of the potential for fires and other mayhem resulting from simple wiring problems and equipment failures.

In this article, we’ll find out how circuit breakers and fuses monitor electrical current and how they cut off the power when current levels get too high. As we’ll see, the circuit breaker is an incredibly simple solution to a potentially deadly problem.

Voltage is the “pressure” that makes an electric charge move. Current is the charge’s “flow” — the rate at which the charge moves through the conductor, measured at any particular point. The conductor offers a certain amount of resistance to this flow, which varies depending on the conductor’s composition and size.

Voltage, current and resistance are all interrelated — you can’t change one without changing another. Current is equal to voltage divided by resistance (commonly written as I = v / r). This makes intuitive sense: If you increase the pressure working on electric charge or decrease the resistance, more charge will flow. If you decrease pressure or increase resistance, less charge will flow. To learn more, check out How Electricity Works.


How Circuit Breakers Work

The problem

It’s a dark and stormy night. You flick on the hall light, plug in the coffee maker and crank up the portable electric heater. You’re starting to feel comfy, when you hear a faint, yet ominous, click—and everything goes black. It’s not a cat burglar or a poltergeist playing tricks with your electrical system. It’s an overloaded circuit being protected by a tripped electrical circuit breaker. Kinda spooky and mysterious, eh? Not if you know a few simple things.

Figure A: A Properly Functioning 15-AMP Circuit

This circuit has wires and an electrical circuit breaker that can easily carry the amperage required by the devices

on it.

What’s a circuit?

When electricity enters your home, it goes to a circuit breaker box (or fuse box in older homes), where it’s divided into a number of circuits. Each circuit is protected by a breaker or fuse. Bedrooms, living rooms and family rooms where only lights, alarm clocks and other small electrical items are usually used are normally on 15-amp circuits. Kitchens, laundry rooms, bathrooms and dining rooms—places where you’re more likely to use toasters, irons, hair dryers and other big-watt items—are usually served by heavier-duty, 20-amp circuits. Major appliances like 5,000-watt electric water heaters and 10,000-watt electric ranges demand so much electricity that they take their own 30- to 50-amp dedicated circuit (See Fig. D in “Additional Information” below), protected by big, “double pole” circuit breaker sizes.

What’s a circuit overload?

The circuit breaker, the wire and even the wire insulation are all designed to work as a system—and that system has limits. Try to push more current through a circuit than it’s designed for and things start happening (Fig. B). Wires heat up under the burden of carrying the excess current. When this happens, the insulation around the wire can degrade or even melt. When insulation melts, current is no longer confined within the wire. That’s when fires start. Luckily, the circuit breaker senses the excess current and “trips” to stop the flow of power before damage occurs

Figure B: An Overloaded Circuit

This circuit has too many energy-demanding devices on it and is trying to carry more amperage than it’s designed for. Things begin to heat up. Luckily the circuit breaker senses this, trips and “breaks” the circuit.

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