Wiring – Is a #14 pigtail to a receptacle on a 20A circuit actually an issue

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I recently had a 15A receptacle in my kitchen partially melt while my wife had our vacuum cleaner plugged into it.

We knew something was up when we smelled the telltale hot plastic smell. I felt the wall-plate and it was hot. I turned off the breaker, took everything apart, and found that the outlet was being used as a pass-through to power two of the counter-top outlets in our kitchen and our very large kitchen refrigerator/freezer.

Supposedly even a 15A outlet is rated for 20A pass-through, but something wasn't right if it melted, so I went and found a replacement duplex outlet, some #14 wire, and re-wired it using pigtails so the outlet wasn't passing through any current.

I wrongly assumed that the circuit was 15A. When I went back to turn on the breaker, I discovered that it was a 20A circuit. Uh oh. My pigtails were under-rated for the circuit.

I also used a take-out receptacle that I had lying around, and it was ivory rather than white.

I told my wife not to plug 2 heavy-duty loads into that outlet until the weekend, and today went out and bought a new white duplex receptacle, found some #12 Romex from which I could cut new pigtails, and rewired it properly, both with the correctly colored receptacle, and with the proper gauge of wire.

I got to thinking, though. Resistance is measured in ohms per foot. A 14 gauge wire carrying a 20 amp load introduces too much resistance over the length of the wire run, causing a significant voltage drop and heating up the wiring and risking a fire.

However, a pigtail is typically less than 4 inches long. I'm not advocating it, but couldn't you use 14-gauge wire for such a short piece of wire and not generate enough of a voltage drop to cause a problem, even if you were to plug 2 devices into the receptacle that drew a total of 20 amps? (Again, I understand that that would be a violation of code, and I'm not about to do it in my house. This is a theoretical question.)

Best Answer

Wire gauge requirements may be due to heat dissipation or voltage drop considerations. Standards can impose restrictions that are not really necessary for a particular situation but accommodating those situations would make the standard too complex.

Let us consider the actual heat generated by using a 4 inch #14 pigtail to carry 20 amps. The resistance of 1000 feet of #14 copper wire is 2.525 ohms. 4 inches would have a resistance of 2.525/1000/3 = 8.4e-4 ohms. The voltage drop is 0.0168 volts and the power is 0.34 watts. Double that for the other pigtail and you have 0.68 watts in your box from those pigtails.

By comparison, the resistance of 1000 feet of #12 copper wire is 1.588 ohms. 4 inches would have a resistance of 2.525/1000/3 = 5.29e-4 ohms. The voltage drop is 0.01 volts and the power is 0.21 watts or 0.42 watts total.

The increased heat load is thus 0.68 - 0.42 = 0.26 watts between #12 and #14.

Related Solutions

Electrical – use the tabs to chain 15A outlets on a 20A circuit

Yes it is sufficient.

A 15A receptacle is designed such that an appliance with a 20A plug should not be able to plug into it. This means that at most under normal operating conditions of a 15A appliance, that the receptacle itself will only draw 15A. If the circuit shorts then the breaker will kick at 20A however.

The tab of a 15A receptacle is designed to handle a 20A load.

EDIT for clarification above: A duplex 15A receptacle contains a tab that connects the hot lead to the hot load. This allows the receptacle to carry the load of another outlet by wiring the lead of Outlet(2) to the load of Receptacle(1). When you break off this hot tab then you are specifically wiring for a switch to control only of the receptacles of the outlet, or you are specifically wiring for each receptacle to have its own circuit on a shared neutral. For two circuits to be wired to a single receptacle on a shared neutral, then you need to ensure that the breakers are on different service legs or you risk overloading the neutral. If you also break the neutral tab then you are wiring the receptacle to have two separate circuits each with its own dedicated neutral. These should be considered fringe cases for residential so it is probably best not to break the tabs if not needed so as to avoid confusing future DIY'ers and licensed electricians. Every time a DIY'er or electrician gets confused then they are potentially risking themselves.

The NEC states that this is acceptable as long as:

The wire is 12 AWG sized for a 20A circuit
There is more than one receptacle on the circuit.

It is important to note that under no circumstances should you install a single 15A receptacle onto a dedicated 20A circuit. This is against code.

210.21(B) Receptacles (1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or where larger than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.

Table:

Circuit Rating (Amperes)
Receptacle Rating
(Amperes)
15 Not over 15
20 15 or 20
30 30
40 40 or 50
50 50

In conclusion, a standard 15A receptacle that one would buy in your hardware store is quality tested and approved to comply with all NEC codes to be legally sold in the United States. If the tab couldn't handle a 20A load without overheating then they would call this out specifically.

Electrical – What size GFCI and receptacles on 20A circuit

If you don't plan on using any 20 ampere cord-and-plug devices, there is no reason to install 20 ampere rated receptacles. Circuits rated for 20 amperes are useful in the home, because they can support more devices. 20 ampere receptacles are often not advantageous, except possibly in a workshop or garage.

Best Answer

Related Solutions

Electrical – use the tabs to chain 15A outlets on a 20A circuit

Electrical – What size GFCI and receptacles on 20A circuit

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