Why do Circuit Breakers Trip?
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Why do Circuit Breakers Trip?

So, you’ve got a tripped circuit breaker. Time to get up off the couch and head to the circuit breaker panel. Once you locate the tripped breaker, you reset it only to have it trip again either immediately, or a short time later.

At this point, resetting it again probably won’t take care of the problem. It’s now time to do a little detective work and figure out why it’s popping in the first place.

As you may (or may not) know, circuit breakers are designed to turn off power to a branch circuit if a dangerous condition is detected on the circuit, thereby preventing the risk of fire. Breakers can trip for any of the following conditions:


Overloaded circuit

Short circuit

Shock potential


Let’s take a look at each of this conditions in some more detail.

Overloaded Circuit

An overloaded is the most common reason for circuit breakers to trip. An overload occurs when a circuit is drawing more amperage that it is designed to carry safely. In most residential settings, the most common breakers are 15 amp and 20 amp sized for lighting and receptacle power. Larger breakers may exist in the panel for specialized equipment such as well pumps, central air conditioning, or electric stoves.

As an example, suppose you have a 15 amp circuit breaker protecting receptacles in your living room. This circuit will allow no more than 1800 watts of power to flow before tripping due to overload (for you math fans, a watt is defined as volts x amps. So, 15 amps x 120 volts = 1,800 watts).

Let’s say you are running a TV that draws 110 watts, two lamps with a 75 watt bulb in each one, and a ceiling light with a draw of 200 watts. Now you decide to plug in an electric heater that draws 1,450 watts. Once you turn it on, the circuit breaker trips. After doing the math, you find that the heater pushed the wattage of the circuit over 1,900 watts. Since this is more than the 1,800 watts the circuit breaker is rated for, it tripped.

Now if someone had installed a circuit breaker larger than what the wire is rated for, you would run the risk of a fire. The larger circuit breaker wouldn’t trip (for instance, a 20 amp breaker can carry 2,400 watts at 120 volts), but the 15 amp-rated wire used to supply that room will overheat and possibly melt and start a fire. So, how is an overload condition corrected? There are a couple of possibilities:

The easiest thing is to turn off anything you’re not using in the room in question and see if that alleviates the overloading condition

Another solution is to unplug a couple of appliances from the circuit in question and plugging them into different circuits in different rooms (rooms that still were working when the breaker tripped).

Loose connections can also create phantom overload conditions, due to wires heating up. Tightening all connections starting at the circuit breaker and then every device and outlet in the circuit will remedy that problem.

Short Circuits

A short circuit is caused when any two current-carrying conductors of the circuit come into accidental contact with each other. A current carrying conductor can be either a ‘hot’ (usu. colored black or red) or a neutral (usu. white colored) wire. A short circuit could also occur within the appliance you may have plugged into a receptacle. Short circuits can cause an incredible amount of energy to be transferred in an instant, usually accompanied by a potentially blinding arc flash and loud explosion. If not protected by a circuit breaker, a short circuit can almost always lead to a fire or other dangerous life-threatening condition.

Many electricians have been severely burned and blinded, and in some cases electrocuted when inadvertently creating a short circuit while working on high voltage equipment.

To diagnose a short circuit:

Confirm the power to the receptacle or outlet in question is OFF at the circuit breaker.

Unplug all appliances that are connected to receptacles on the circuit in question.

Turn the breaker back on.

If the breaker stays on, then you may have a short circuit within one of the appliances you unplugged. Check each one for signs of damage, abuse, or excessive wear.

If the breaker still trips-

You may need to check all devices on the circuit (switches, receptacles, fixtures, etc.) for signs of trouble such as loose connections, frayed or damaged wiring, wires touching each other inadvertently. This last step may require the assistance of a licensed electrician if you are uncomfortable with these advanced troubleshooting methods.

One thing you may find interesting. The electrical industry, realizing the amount of damage caused yearly by short circuiting, has come out with new requirements to help protect against these types of problems. The most significant is the requirement to install arc-fault circuit interrupting (AFCI) breakers in most areas of the home. The breakers are very sensitive to the effects of arcing wires and can trip much quicker than a standard circuit breaker, thus preventing many more instances of fire.

One other situation that can cause a circuit breaker to trip would be a ground fault condition. A ground fault is when current does not follow the normal path to ground; rather it takes some other path, such as through the metal frame of an appliance, or in some cases, people can become the return path for fault current – a current flow of as little as 5 thousands of an amp (0.005 amp) is enough to cause a person to go into cardiac arrest. This is less than the power used to light a 5 watt light bulb!

Unfortunately, standard or arc-fault circuit breakers cannot detect this type of fault and can’t adequately protect a person from electrocution. However, ground fault circuit interrupting (GFCI) circuit breakers are designed to specifically look for this type of fault and trip the breaker, thus shutting off power to the circuit.

Remember: standard and AFCI breakers protect property from fire. GFCI breakers protect people!

When diagnosing a ground fault, you would follow the same methods that were used above in determining the source of a short circuit. The only difference you may notice is that if the problem is determined to be from an appliance that was plugged in, you might find that the appliance seems to work perfectly fine on a circuit that is not protected by a GFCI circuit breaker. That doesn’t mean that there isn’t a problem with that appliance! What it indicates is that there is enough ‘leakage’ current within the frame or some portion of that appliance that is not following the normal path to ground, and it has the potential to fatally shock the user. It is strongly recommended to discontinue use of such an appliance, and have it repaired or replaced.

One last reason you may see a circuit breaker trip is due to overheating. When a circuit breaker is operating continuously near its maximum temperature rating, the internal mechanisms may more readily trip due to the high ambient temperature within the molded case of the circuit breaker. Circuit breakers may overheat for a couple of reasons:

1. if there is a continuous load on the circuit that is at or near the trip rating for the breaker;

2. if the connections are loose on the breaker.

Nuisance tripping due to loads running at or near the maximum rating of the circuit can be cured following the suggestions listed for overload tripping above.

Loose connections are easier to fix, if you catch them in time. When a terminal screw is not tightly secured against a wire, what will happen is that over time, this wire will become loose in the terminal. When the wire heats up (such as when it is under load) it expands and pushes against the screw. Later when the load is shut off and the wire contracts, the gap between the wire and screw becomes a tiny bit bigger. Eventually, enough instances of this cycle occurring will cause a big enough gap between the wire and screw terminal to allow a spark to occur when the load is turned on. The sparking will eventually become a constant buzzing or crackling within the panel. This action creates heat within the breaker and may cause it to trip. Tightening the screw connections prevents this problem from getting worse.

If the problem goes unchecked, eventually, that constant crackling works kind of like a low-energy arc welder. It will begin to degrade components of the circuit breaker (and possibly even the bus bar of the panel) to the point where it can no longer be fixed by tightening; the breaker (and possibly the service panel) would have to be replaced in its entirety.

For more information about circuit breakers, including how to reset a tripped one, visit this page.

Wurtsboro Electric Service, Inc.

Licensed electricians serving Orange county, Sullivan county, and Ulster county in New York
(845) 888-8000 

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