Can I safely use a #12 extension cord on a 15A circuit temporarily for extended periods?

Question

Is it okay to use an outdoor 25 foot 12 gauge extension cord for an outlet to appliance (temporarily) to make sure there will be no overheating of any wires, which will be running on a 15 Amp Circuit (which probably has 14 gauge wire inside the outlet within the walls)?

In other words, would this be dangerous, being the circuit breaker might not detect overheating (if any) during an extended period of continual usage?

As I mentioned, that the wall outlet leads to a 15 amp circuit, all my 20 and 30 amp circuits are used to the max).

I have used several 6ft 14/3 gauge extensions listed for 15A with a max of 1875 watts, of course this is bad, at each end they heat up and is very dangerous, because of the resistance. I was think a heavier wire - directly from wall outlet to appliance might be better (for now). Thanks in advance

Answer 1

The heavier wire (12 AWG as opposed to 14 AWG) wire in the extension cord will reduce the resistance of the cord. For a given load there will be less heating in the cord. However you should consider using as short of cord as possible. Don't use a 25 foot cord if a 10 foot one would work instead. Half the cord length half the resistance.

Be aware that if such extension cord heats up too much it is likely that you are putting too much load on the circuit and the wires in the wall are going to be subject to heating as well. Over heating electrical circuits are dangerous and can lead to fires.

Answer 2

Am I reading this question correctly? From what I am seeing in your question. You are connecting a #12 gauge extension cord to a 15A circuit feeding a receptacle. If so your overheating is in the internal wiring from your receptacle to your breaker and no oversizing of an extension cord is going to prevent it.

Example: You have a 1/2" water pipe with x amount of pressure and it produces y amount of GPM. Adding a 3/4" pipe to the end of it is not going to change the GPM.

When an electrician looks at providing a circuit for an appliance he must have Nameplate Ratings in HP or VA or Watts, and the length of the circuit to determine the correct overcurrent protection and the correct wire size. Not much else matters other than that.

Also, FYI a breaker is an overcurrent device not a heat detector. In fact it is the opposite of overheating, more current flow causes the breaker to trip. Overheating is a sign of increasing resistance and restricts current flow. So unless the breaker is sustaining damage by overheating, it will not trip.

Answer 3

It is perfectly OK to use a 25 ft 12 ga extension cord on a 15 A circuit. If 25 ft is longer than needed you do not need to go to the trouble and expense of buying a shorter one. A 12 ga cord is a very heavy cord.

Of course, if this cord goes across where people walk, this could be a tripping hazard to someone walking over the cord. You might want to get one of those rubber covers to reduce risk of tripping and protect the cord.

It is normal for a cord to a high current device to get warm to the touch and this is not dangerous or especially wasteful of electric power. I have a 120 V 1500 W electric heater ("Sunbeam" made in China) and its cord gets quite warm to the touch when the heater is on high.