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Circuit Breakers and Short Circuits

circuit breaker

Below we've provided a non-technical overview into circuit breakers and short circuits. The objective was to impart understanding of circuit breakers and what they offer for the Do-It-Yourself homeowner. This article is not meant to be an all encompassing deep-dive into the nuances of electrical engineering. It is meant to give the reader a simplified overview into these common household devices found in the USA and elsewhere.

The subject of harnessing and routing electricity to a device (a lamp for example), how this routing is accomplished and how it is explained can generate controversy. If there's a better way to explain it in layman's terms let us know! We'd really be impressed if you used everyday language that everyday people can understand.

Here we go...

Voltage - Think of voltage as a two-lane highway with a defined speed limit.

Amperage - Think of amperage as being how few or many cars are traveling down the highway at any given time based on the size and speed limit of the highway.

Short Circuit - Think of a short circuit as unapproved and unfunded road construction on the highway that leads to nowhere, or ground.  A short routes the amperage-traffic away from its final destination and does so beyond the defined speed limit.  The path of the electricity is “short” or “shortened” by the presence of construction and stops electricity from reaching its final destination.

All short circuits are a detour to ground. If you've ever been shocked working with electricity it is because you were grounded – your body was the short circuit. Workers repairing high tension wires by hanging off the side of a helicopter can touch the wires with voltage present because their bodies and the helicopter aren't grounded.

Touching a screwdriver to a live, bare wire may not cause a short circuit. Further touching the same screwdriver to a grounded metal casing will cause a short.

Circuit Breakers - A circuit breaker is like a traffic signal that stays green when traffic is flowing smoothly and turns red, or trips when it isn't. A circuit breaker mechanically "breaks" the flow of electricity through an electrical circuit. A tripped breaker creates a small gap internally that stops the flow of electricity. Resetting a breaker usually resolves the "break" in the circuit and allows electricity to pass uninterrupted.

A breaker can be turned on and off and stops the flow of electricity to an electrical component such as a light, plug or any one of thousands of other devices. The difference being that a circuit breaker has the ability to sense problems either coming from an upstream source (too much amperage for example) or downstream from the device being powered, again too much amperage or if wires with electricity in them touch a grounded object the circuit breaker can sense this and react to the problem.

Circuit breakers are fail safe devices and serve to protect a list of components and infrastructure from damage due to high amperage being present. They can even be life saving devices. Your hair drier has a circuit breaker contained within its plug to protect the user from electrocution since hair driers are often used near basins containing water. Drop a working hair drier into a full bathtub and the breaker should trip.

A circuit breaker that switches off by itself is considered "tripped," "open," or "off" and these terms are used interchangeably. A circuit breaker that is energized and passing electricity through it is "closed" or "on." Most circuit breakers in homes are labeled "on" and "off" to indicate the status of the breaker and they have an amperage rating, most are 15 to 20 amp (amperage) breakers.

Circuit breakers behave best when there is a sudden and dramatic change in the amperage being passed through the breaker. For example, if a sudden surge of amperage from an electrical motor occurs the breaker can and probably will trip.

The Bad News About Breakers

The problem with breakers is that they're not very good at dealing with amperage that slowly rises over a period of time. When we say "amperage that slowly rises" we're talking about seconds or minutes rather than milliseconds. A sudden amperage overload that occurs very quickly will cause a breaker to respond just as quickly by tripping but it has to be a big punch before the breaker will trip.

The burned wire shown at the beginning of the Furnace Short Circuit project encountered a slow rise in amperage – the breaker never received the big amp punch it needs to trip and allowed amperage that was too high to continue to flow. The wire melted due to a rise in amperage but it wasn't sudden enough for the breaker to react.

The Good News

On the one hand circuit breakers are very useful and usually protect the wiring and the components being powered from unexpected problems with the flow of electricity. On the other hand there's only so much trust that can be afforded to a breaker. The Furnace Short Circuit project is one example of why you'd want to rethink the infallibility of a circuit breaker. We've experienced a number of melted wires on our boat – the circuit that powers the trolling motor for example. As the batteries that service the trolling motor slowly failed a number of wires melted due to a slow rise in the amperage being pulled through the wires. We rectified the problem but the point is that breakers are good at what they do when the conditions are right; and the conditions aren't always right.

Basic Troubleshooting

First, we always assume that if a circuit breaker has tripped there is a reason for this occurrence and we have to find out why it tripped.

Here are a few of diagnostic steps you can take to test a circuit breaker and related components such as household plugs, light sockets, and wall switches:

  1. If a plug goes dead find another working appliance and plug it into the same plug where the problem revealed itself. Wall-plugs almost always contain two receptacles and you should test to see if one or both of them are dead. If one is dead and the other is working the problem is most likely with the wall plug. If they're both dead try other plugs that are in close proximity; if more than one wall-plug is dead the circuit breaker is probably tripped. Don't forget to plug the original appliance into a known working wall-plug to confirm that it works too. If it fails this test the appliance is probably the source of the problem.
  2. If the appliance and receptacles are all dead it could mean that the appliance itself caused the circuit breaker to trip and it is the root cause of the problem.
  3. As we've mentioned, circuit breakers are labeled with an amperage rating. Circuit breakers often have more than one wall-plug or light switch connected to them in a daisy chain fashion. A wire inside the wall runs from the circuit breaker to a wall-plug. Another wire runs from this wall-plug to another wall-plug and so on. They are chained together. The idea is that the occupants of the house will most likely never exceed the amperage rating of the circuit breaker during normal use of the various wall-plugs.

The Overloaded Circuit Breaker

However, if you plug a vacuum into one wall-plug, a toaster into the next wall-plug and a hair drier into the one after that and turn them all on the odds are very high you will trip the breaker (if the wall-plugs are all connected to the same breaker). These appliances use a lot of amperage and will probably exceed the rating of the circuit breaker. It could be just poor timing with everything running at once or you're going to have to find a different way to power your appliances.

When troubleshooting dead wall-plugs it is useful to know what appliances were being used at the time of the failure and whether they were plugged in in relative close proximity to one another. In theory there should be a logical progression with wall plugs and how they are wired together but it's really just a best guess since you can't see the actual connections behind the walls and determining the exact configuration takes a bit more work to figure out. However, at least being aware of these limitations might help you solve electrical problems.

If your diagnostic steps are leading you to the circuit breaker it's fairly easy to visually inspect the main panel for a tripped breaker. Begin by making sure there are no sign of high heat near any of the breakers – a yellowish/brown or black residue may be present and the source of that problem needs to be determined. If you've just overloaded the circuit with too many appliances the switch on the breaker will be in a different position than all of the other breakers. There may also be a small plastic site-glass on the breaker with a dayglo-orange background that allows for easy identification of problem breakers.

The breaker switch may or may not be in the off position. It may be sticking straight up mid-way between off and on. If this is the case switch the breaker to off first and then to on. The breaker should stay in the on position. If it trips immediately more diagnostic work is needed. If the circuit continues to run for a short period you've probably just overload it and resolved the problem.

We'll talk about taking additional step to resolve tripped breakers and short circuits in future articles.