Wiring – 14ga wire with 12ga wire

wiring

House built in the 1940s. When remodeling a bathroom, I put a 20A circuit in the panel and ran new 12/2 wire up to the bath to GFCI outlets. I continued the circuit up into the attic to power an attic bathroom exhaust fan.

In the attic there is a rickety old pull-chain light fixture attached to the original 1940s wiring, which has two conductors but no ground. A prior owner of the house attached 14/2 wiring to this old 1940s wiring, and had simply tied the ground wire of the 14/2 to the junction box.

I would like to detach the 14/2 from the ungrounded old wiring and attach it to the new 20A 12/2 wire in the attic.

All the receptacles on the 14/2 are 15A.

Does mating 14/2 to 12/2 present any safety hazards if nobody tries to draw more than 15A on the "extended" 14ga leg of the circuit?

Best Answer

Nope. Any circuit with any 14 AWG wire in it, is a 15A circuit. it requires a 15A breaker and cannot have 20A receptacles.

You cannot put a non-bathroom load on a bathroom circuit. Whatever circuit now powers this attic light, leave it that way unless you want to pull another circuit. And if you do, go ahead and pull 12 AWG. You can always use larger wire than required. It will still be a 15A circuit as long as it still has any 14 AWG.

Share the ground!

You are welcome to use the ground in the bathroom circuit to provide ground to the ungrounded attic light circuit, provided both are supplied out of the same breaker panel. This is a ground retrofit, and the rules (NEC 2014) now give you wide latitude to do this. Your 12 AWG ground wire is enough to ground any 15A or 20A circuits (plural) served by the same panel. Doing so should not affect your GFCI, even if the old circuit has a problem.

The circuits need to come out of the same panel, so if the circuit breaker for one is in a main panel, and the other breaker is in a sub-panel, then no.

Bathroom circuits

Code originally required a dedicated circuit for bathroom receptacles. It could serve as many bathrooms as you wanted, provided it served only receptacles. Obviously this necessitated a second circuit for lighting and fan. This could be taken off a circuit for another room.

Later, Code was revised to allow a different arrangement: the dedicated receptacle circuit could also serve other bathroom loads, if it served only one bathroom. Other loads might include lighting, fan, etc.

Bathroom loads are ones that exist to serve the bathroom and are used whilst in the bathroom. A bathroom fan is, but an attic light is not.

50% limit on fixed loads

This comes up anytime you have a fixed, installed, built-in load that takes a lot of power. In bathrooms this could be a heat lamp or air heater, or point-of-use water heater. If are circuit has fixed (built-in) loads which total more than 50% of circuit capacity, in other words 1200W on a 2400W circuit, *then you can't have any receptacles on that circuit

You can piggyback other fixed loads on that dedicated circuit, as long as you remain under 80% of circuit capacity (1440W for 15A, 1920W for 20A).

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 – connect a combination heater/fan unit to the existing bathroom wiring

In this case, it looks like you'll have to run a new 20A circuit. As per Article 110.3(B) of the National Electrical Code (NEC), and the manufacturers instructions.

NEC 2008

110.3 Examination, Identification, Installation, and Use of Equipment.
(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

On page 5 of the manufacturers installation manual ^(PDF), it clearly states that you must use a 20A circuit.

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