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Two new 20A circuit was run to service a new office / rec room in a basement. There's 5 receptacles on each of them. The receptacles installed are 15A tamper resistant. On each of the circuits, one of those receptacles might be used for a space heater on occasion. Doesn't need to be a heavy duty or hard-wired one necessarily, a 1500W personal space heater would suffice and even those can run 1300W. Still, it seems prudent to have a 20A receptacle, on a 20A circuit, when any kind of electrical heating like this is a use case?

For that reason I'm thinking one of the 15A receptacles should be replaced with a 20A receptacle. The horizontal-slot in the 20A receptacle isn't needed since most space heaters I've seen have a 15A-style plug, but that horizontal would show which receptacle is rated for 20A use.

I know it's okay for 15A receptacles to be on a 20A circuit, and that's been answered thoroughly here before. But is it okay to mix a 20A receptacle in with mostly 15A receptacles on a 20A circuit?

cr0
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2 Answers2

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TL;DR 15A receptacles are all you need. Just get good ones.

This is already handled very well in code. With most circuit sizes, the receptacle type must exactly match the circuit size. For example, you can only have 15A receptacles on a 15A circuit. However, you are allowed to have 15A receptacles on a 20A circuit provided there are at least 2 receptacles on the circuit. That can be as little as a standard 15A duplex receptacle - while that is one "device" it counts as the 2 receptacles it actually contains when it comes to this particular rule. You can have 1 or more 20A, 2 or more 15A, or any combination of 15A and 20A.

The basic problem is a Catch-22: So many houses have had only 15A circuits/receptacles for so long that manufacturers of 120V plug-in consumer-grade appliances simply don't manufacture much that requires a 20A circuit because that would severely limit market share. And the cycle continues - people don't install 20A receptacles (since they don't have to) because they have nothing to plug into them except 15A appliances.

However, the 20A circuits are still useful. They are required for new circuits in bathrooms and kitchens and certain other places, not because of a great need for 20A appliances - we already established that's not the case - but because it allows multiple appliances without overloading circuits. Or at least with a lower chance of overloading circuits. Two examples:

  • 1875W hair dryer + other stuff. On a 15A circuit that would be the limit. Which means that if you add even a little bit extra - lights, fan, electric shaver, etc. you start to go over 15A and risk problems. With a 20A circuit you have an extra 5A to work with and you are fine unless you plug in two hair dryers, or a hair dryer and curling iron, at the same time.
  • 1500W space heaters. I hate these things with a passion. But sometimes they are a necessary evil, particularly if your furnace dies on a cold day. They are limited to 12A because they can run for a long time (unlike a hair dryer), which is why they are pretty much all 1500W. If you run 2 of them on a 15A circuit then that's 24A and you're going to (hopefully) trip the breaker very quickly - and if you don't then the 14 AWG wire will overheat. If you run 2 of then on a 20A circuit then you have a little breathing room. You will probably trip the breaker eventually but a few minutes of running them probably won't and it is definitely safer. (But please, if you plan to use multiple space heaters run multiple circuits.)

We've established that 15A receptacles are allowed on a 20A circuit and that they can be useful on a 20A circuit. So that just leaves the receptacles themselves. Because of this rule allowing them on a 20A circuit, they are actually designed to allow 20A to pass through the device. There really is no functional difference other than the extra slot to allow 20A plugs to fit.

If you want some extra safety, stick with 15A receptacles but go to better quality receptacles. Basically instead of the (current Home Depot pricing, but while the prices will change the concept will likely exist for a long time) $ 1.50 residential grade 15A tamper-resistant duplex receptacle, go for the $ 3.42 commercial grade 15A tamper-resistant duplex receptacle. For the extra money you get "screw to clamp" instead of "backstab", self-grounding (saves a connection if you are using metal boxes) and a much more rugged/long-lasting design.

manassehkatz-Moving 2 Codidact
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On a 20A circuit with at least two outlets you can mix 15A and 20A outlets any way you want. All 15, all 20, or any mix.

There is no point putting a 20A (5-20) receptacle in the circuit if you have no appliances with a 20A plug. It accomplishes nothing. They are not better, they can both be purchased at various levels of quality. If you buy a 15A and 20A outlet of the same make and construction, the 20A one is capable of accepting a 5-20 plug, and the 15A one is capable of preventing that. That's the only difference.

If you think you might buy an appliance with a 20A plug you need to give more thought to what is practical and manageable, rather than what is allowed. If you are provisioning for a (probably) 1920W heater with a 20A socket for it, it should probably be the only outlet on the circuit, unless you plan it purposefully, EG, the only other outlet is for something that would not be used at the same time, like a window air conditioner. Don't install new outlets that, from the start, will require end-users to dance around the circuit capacity. .

jay613
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