Can you use 15A outlets on a 20A circuit with 12-2 wire and a 20A breaker and how many outlets would this allow?

Answer 1

I'm going to assume you are referring to residential construction because rules for commercial and industrial settings can be different. Also rules differ by geography (i.e. Canada specifies a maximum of 8 outlets on a 15 amp circuit, USA code is silent on the issue but for practical purposes, more than about 10 will likely lead to poor performance. Some code also specifies max loading of a 20 amp circuit at 80% making 10 outlets the practical limit if using 20 amp outlets on that circuit.

To expand on the previous answer a little, there is a large margin of safety in the construction of these components but if you think about it, you are placing a component that is rated at 15 amps into a 20 amp circuit. That outlet is potentially the weakest link in the circuit and could act like a fuse. If any of those 15 amp outlets are overloaded, it might overheat and fail before the circuit breaker. This is a recipe for a fire. You may think now that you'll remember to only plug in light loads, but these things have a habit of growing.

You can plug typical small home appliances (lamp, stereo, TV, etc.) into a 20 amp outlet so the only benefit in using the 15 amp outlet is the minor cost savings at installation. If it were my building, I wouldn't risk it.

If I can't talk you out of doing this and it's allowed by your applicable code, make sure you don't daisy-chain the circuit through the outlets. (In other words, don't run your 12-2 wire in one side of the outlet and out the other side.) Instead, use a pigtail (short piece of wire) to tap off your line to each individual outlet.

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In the United States you can run 20 amp breakers with 15 amp outlets but not in Canada. And for how many? About 10 to be on safe side as long as they are all low amp usage appliances. TVs, steros, fans, lamps.

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You can run 20 amp breaker with 12-2 wire as long as you make sure you use the 12-2 wire that is rated at 20 amp.

Whilst this was not your exact question it is worth saying IT IS NEVER SAFE to run a 20 amp load through a 15 amp receptacle. It is only rated to handle up to 15 amps.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,
on electrical circuits, equipment or appliances,
always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.

Answer 2

Yes. The breaker can be smaller, but not larger than the circuit it is protecting. The situation you describe would normally be protected by a 20A breaker, but what you suggest is fine. You couldn't go the other direction and use a 30 A breaker because it wouldn't protect the lesser rated components.

Answer 3

It depends on if you have a single outlet (receptacle) on a branch or multiple receptacles on a branch.

One receptacle on a 20A branch: The receptacle must be rated 20A

Two or more receptacles on a 20A branch: The receptacles can be 15A or 20A

Technical Reference: 2011 NEC

210.21(B)(1)A single receptacle installed on an individual branch circuit shall have an ampere rating not less that that of the branch circuit.

210.21(B)(3) 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 rated higher than 50 amperes, the receptacle rating shall not be less than the branch circuit rating.

Table 210.21(B)(3)

20A Circuit Rating 15A or 20A Receptacle Rating