If you’re like most homeowners, your circuit breaker panel is probably crammed full of breakers. But what happens when one of those breakers gets too hot?
It’s normal for a circuit breaker to get a bit warm when the circuit is in constant or heavy use, but it should not be allowed to get too hot.
Breakers are designed to protect your appliances and circuits from too much current and heat and prevent a fire. A circuit breaker is a safety buffer between the house and the power line. If overheating happens often, and it’s secure inside the panel, and the wires are tight, something might be wrong.
A circuit breaker is too hot when constantly close to its tolerable limit or rated value for current flow. If it exceeds this, which it should not if the circuit breaker is working properly, it will likely overheat and catch fire. Normally, the maximum temperature it can endure safely is 140°F (60°C). Otherwise, it should trip to stop the current flow if operating properly. This happens because the bimetallic strip inside it curls to break the circuit.
Below I will show you ways to tell if a breaker is too hot, why it happens, what happens inside, and what to do if it does.
How Can You Tell if a Circuit Breaker’s Temperature is Too Hot
To tell whether a circuit breaker is too hot, you must get an indication of or measure its temperature.
Normally, a circuit breaker’s operating (surface) temperature is 140°F (60°C). The closer the temperature gets to this limit, the warmer the breaker will be. If it gets very close or reaches the limit, it is likely too warm, so the breaker will trip to prevent it from getting hotter and catching fire.
However, if the breaker fails to trip, it may be faulty, so a temperature that is too high could be a fire hazard.
Using the Back of Your Finger
Gently touch the circuit breaker with the back of your index finger.
If the breaker is warmer than usual, it might be too hot. If your finger gets burned or near burned, you can be sure it is too hot, which could be wrong.
Using a Thermometer
You can check the temperature of a circuit breaker using an ordinary thermometer. Place the tip of the thermometer on the breaker and take a reading.
The actual temperature you read this way is its surface temperature rather than the temperature inside the breaker.
Using a Thermal Scanner
Another tool you can use instead of a thermometer to check a circuit breaker’s temperature is a thermal scanner. It can be a safer method than the others because you don’t have to touch or get close to the circuit breaker.
Laboratory Testing
Most people won’t have access to this method but will list it for the sake of discovery. Laboratory testing of circuit breakers is done using a temperature-sensitive instrument.
Why a Circuit Breaker Gets Too Hot
Overloading
The most common reason for a circuit breaker getting too hot is overloading.
You might be drawing too much current through it. This often happens when too many appliances or electrical devices are plugged into the circuit together and used simultaneously.
Overloading a circuit generates a current that could get very high, which is what generates the heat. If this leads to overheating, the circuit breaker will trip.
The solution is to reduce the load. You can do this by reducing the number of appliances on the circuit, and if there is one that requires a lot of power, put it on a separate dedicated circuit.
Heavy Load
A heavy load in a circuit occurs if an appliance requires a lot of power.
An appliance should draw no more than 80% of the circuit breaker’s rating for continuous use. For example, a 15A breaker has a usable limit of 12A, and the current should not exceed 16A on a circuit with a 20A breaker. You can go over these 80% limits temporarily but not for long periods, and you must not exceed the maximum rating.
A Poor Connection
Another possible reason a circuit breaker gets too hot is a poor connection somewhere along the circuit. (1)
You should check for a poor connection if there is no overloading or heavy load.
A weak joint can cause a poor connection, a wire not joined to a plug’s pin firmly, or a loose screw on a screw terminal. All of these weaknesses can cause a temperature rise.
Weak Circuit Breaker
Circuit breakers are usually reliable, but they can weaken over time.
If a circuit breaker is of poor quality or very old, especially if it’s over ten years old or has been enduring a constantly high load, it may be weak.
In all these situations, the breaker will be unable to handle the current load as usual, and it might get too hot frequently.
Short Circuit
A short circuit somewhere along the circuit protected by a circuit breaker will cause the breaker to heat up instantly and trip.
Loose or Damaged Wiring
If there is any damaged wiring along a circuit, it will affect the circuit breaker.
A wire might get damaged if, for instance, you accidentally drill through a conduit or a rat chews through it. But it can also happen over time if the wiring is old or the insulation is poor.
While the circuit is functioning, the current draw will be higher than normal so that the circuit breaker will be warmer than usual.
What Happens to the Circuit Breaker
Having read this far, you know that a circuit breaker trips to prevent a fire hazard when it gets too hot.
But what happens inside the circuit breaker when the temperature is too high, or how does it detect a dangerous temperature level to make it trip?
A temperature sensor inside it detects when the temperature level is too high and if it needs to break the circuit by tripping. Circuit breakers are always connected to a circuit in series to ensure they will always operate and can detect the total current in that circuit. Like fuses, which contain metal alloys, circuit breakers contain bimetallic strips.
When the strip gets too hot, it curls according to the coefficient of expansion of the two metals it comprises. It is this curling that breaks the circuit. (2)
What To Do If a Circuit Breaker Often Gets Too Hot
If you find that a circuit breaker is often warm, even if it does not trip, you should investigate the circuit to check if any of the above reasons apply.
If it does, for instance, if there is overloading, a heavy load, or loose wiring, then fix that problem. If the circuit breaker itself is weak, then it should be replaced. The important thing is ensuring everything is as it should be, so the circuit breaker does not get too hot.
Circuit breakers are designed to protect your home, appliances, and you, so look after them too.
References
(1) Larry Dimock. Circuit down. Lulu.com. 2007.
(2) John R. Fanchi. Energy technology and directions for the future. Elsevier. 2013.
Video Reference
CNC Electric
