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What makes Circuit Breakers Important?

We interviewed some companies
about their circuit breakers and electrical
systems and were shocked to find that some of them
didn’t have a trained electrical safety inspector or have any idea how their electrical system even worked. There is a shortage of trained electricians who know how a substation operates, so we think it is best to write this guide so anyone can understand how their electrical system works, what dangers are present when working with them, and how to know when it needs to be professionally serviced.

Circuit breakers are the focal point of electrical systems. Breakers are crucial for electrical safety. All they do is break the current if there is too much load, like a sudden surge of energy or a ground fault.  There are a few types of breakers that you might come across:

-Low voltage air circuit breakers for less than 1kV use the air to dissipate overcurrent when it trips. These include miniature circuit breakers which are thermal or thermal-magnetic and are rated up to 125 amps, molded case circuit breakers rated up to 1,600 amps, and low voltage power circuit breakers that you find in switchboards and switchgear cabinets.

-Medium-voltage breakers can be rated between 1 and 72kV. There are oil filled units, sulfur hexafluoride units, air units, and vacuum units. They use separate current sensors and relays instead of built-in sensors.  

-High voltage breakers protect large power transmission networks. These breakers should only be handled by qualified personnel.

-Solid state breakers are a new digitalized style of breakers that cut down on trip time and can monitor current loads.

-Magnetic breakers use a solenoid to trip the breaker. It is an electromagnet that is pulled harder when the current becomes stronger, and when the magnet reaches its maximum length for the current rating it pulls a latch that opens the contacts, cutting the circuit. These are the most common breakers in the US.

-Thermal-magnetic breakers are more common in Europe and are meant to allow smaller overloads to happen more often but trip quickly under a bigger load. These allow for short surges like when a motor starts up.

-Magnetic-Hydraulic breakers have a solenoid coil that is slowed by a fluid to allow for short surges. This breaker style is incorporated into large breakers over 1000 volts. Some of these use oil to extinguish arcs.

-Ganged breakers are like the double tied together switch in your breaker box at home. These just ensure that if one pole goes overcurrent, all tied breakers will trip.

-Shunt trip units are like a normal breaker but are used to cut power in an emergency.

Let’s break down the typical low voltage breaker you find in the commercial and industrial setting. These are usually 3-phase breakers and can be open case or molded case. There are many still in service that are decades old. These breakers can be found inside of metal-enclosed switchgear, in individual enclosures, or stationary mounted.  You don’t typically see very much of the breaker when it is in operation, just the front cover which usually consists of a charge handle or button, a trip button, and some stickers or plates with information about the breaker on it. You might also find a second button for discharging the breaker, a racking mechanism used to take the breaker out of its housing, and a retrofitted trip unit.


Inside the breaker it might seem complicated, but really it’s just a bigger version of the breakers in your own house. It works like a mousetrap, if too much load is put through it, it will trip. Strong springs decompress and instantly separate the “contacts”-copper plates that transfer voltage through the phases-and cutting the circuit. Any excess electricity travels up into what is called an “arc chute” like a Jacob’s ladder and is dissipated. Other breakers work with a similar formula, utilizing their own method to cut the circuit and dissipate the arc.

There is four ways for a breaker to trip: long time delay, short time delay, instantaneous, and ground fault. You can find these settings on the trip unit if the breaker has one. When the breaker goes under high load, it begins counting. The trip unit tells the breaker what amperage to start counting at, and how long it should count until it trips. Only a qualified professional should change trip unit settings, for doing so without the full knowledge of how the breaker is operating can cause serious injury to yourself and others as well as damage your building and equipment.

The most dangerous event that can happen with a failing breaker is known as arc flash. Arc flash happens when an electric current suddenly leaves it’s intended circuit and travels through the air to another conductor or the ground. Arc flash can be violent and cause severe injury or death. OSHA lists potential arc flash causes to be: dust, dropping tools, accidental touching, condensation, material failure, corrosion, and faulty installation. It is important to therefore determine the safe boundaries which you should stay away from energized equipment and discuss this with anyone who may encounter such equipment. You can find more information about arc flash safety from OSHA here Microsoft Word - HANDOUT Arc Flash.doc (


Other hazards involved with circuit breakers include electric shock, pinch points in the mechanism, and a chance of small exposure to toxic materials when handling damaged parts. Never put your hands in a charged breaker, even if it is detached from the switchgear.

You should have your breakers tested at least once every five years.

There are many factors that can inhibit a breaker from tripping when it is supposed to. This includes old, worn, and broken parts, corrosion, hardened grease, missing hardware, loose wiring, and typical wear and tear. These can be accelerated if your building is prone to very dusty, dirty conditions or if the area your breakers are in isn’t temperature controlled. Some symptoms of a failed breaker include maloperations of electrical equipment or equipment running off the breaker, excessive breaker trips, breaker not staying in reset mode or not closing, abnormal noise, excessive heat, a burning smell, or fire.  You don’t want your breaker to trip too soon because outages cost you time, and you don’t want it too late because that can cause dangers resulting in equipment damages and personnel injuries. If you feel like there is something wrong with your breaker or are unfamiliar with your equipment, the safest option is to have it tested by a professional right away.

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