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I have a new -80 deep freezer that calls for NEMA 6-15R receptacle, but the old one it is replacing called for a NEMA 6-20. I note that the plug actually seems to fit in the 6-20, but is there a reason that this would cause a problem? The machine should only draw the lower amperage, so the fact that the outlet is overrated wouldn't be a problem?

Maybe I'm missing something.

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tl;dr

15 Ampere cord-and-plug appliances can indeed, safely be connected to 20 Ampere receptacles.

A deeper understanding

NEMA 6 is a design standard for three wire grounded cord-and-plug devices and receptacles. The number after the dash (-), is the current rating of the device. For example. A NEMA 6-20 device, would be a three wire grounded cord-and-plug device capable of withstanding 20 amperes of current. The "R" simply tells you that the device in question is a receptacle. A NEMA 6-20 cord-and-plug device, would plug into a NEMA 6-20R device.

The NEMA design standard is a safe and convenient way to determine what can connect to what. Basically, if it fits, it works.

If a 15 Ampere device is connected to a 20 Ampere rated receptacle, the device will still only draw a maximum of 15 Amperes. Plugging the device into a higher rated receptacle, will not cause it to draw more current.

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  • Good to know. I'm talking to the manufacturer rep now, and they are implying that it should only be plugged into 6-15, not a 6-20 (I specifically asked). I'm trying to be escalated up the support to see if they can give me a reason, but it seems like it should be fine. (Can't accept your answer yet due to time). – Atl LED Jun 24 '13 at 17:40
  • Thanks for the deeper understanding. That was my impression, and I feel like I'm being fed something from the manufacturer where there is an answer in a customer service book, not someone who understands the electronics. – Atl LED Jun 24 '13 at 17:52
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    Perhaps the manufacturer of your freezer failed to include any over-current protection in their product. Perhaps its internal wiring is only safe to 15 amps and they depend on your 15 amp breaker enforcing that limit. I doubt it. But that's the most likely reason they might actually want you to not plug it into a 20-amp circuit. More likely though, the rep you spoke to is talking out of his rear. – Billy C. Dec 13 '16 at 23:43
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Ideally, a fuse or breaker should not be rated higher than the weakest link in a system.

If a piece of equipment is rated below the fuse or breaker rating, it becomes a sacrificial device in the event where it draws more than its current rating but less than the fuse or breaker rating.

A device rated for a NEMA 6-15R receptacle that is connected to a NEMA 6-20R receptacle will be allowed to operate within its design parameters, but will also be allowed to draw current above its design parameters.

Edit: Many devices have built in protection allowing them to be connected to a variety of sources. The notes above pertain primarily to pieces of equipment that do not have built in protection and rely on the source protection.

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    So I shouldn't plug my 0.5A lamp into a circuit protected by a 15A breaker? I should instead plug my five 0.5A lamps, into a single circuit protected by a 0.5A breaker? – Tester101 Jun 25 '13 at 17:58
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The fact that your NEMA 6-15 plug physically fits in a NEMA 6-20R receptacle tells me it is a supported configuration.

Note how a NEMA 6-20 plug will not physically fit in a NEMA 6-15R receptacle.

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The outlet is not the fuse or the breaker, so as long as everything is rated it'll be fine. Going larger on wiring or outlets is only insurance, it cannot hurt a thing. The breaker or fuse is what is limiting the circuit's capacity as is desired. You would never want the wiring to be the weakest link. It is the same with doing a job to code, code is the minimum standard.

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Just make sure that if you are "close" to the rating of the circuit breaker that you have the appliance on a circuit of its own. In your case, having a 15 amp appliance on a 20 amp breaker (assuming the receptacle is the same as the breaker) will cause you no problem. However, if you should put two 15 amp devices on the same 20 amp breaker, you could conceivably have a current draw of up to 30 amps, causing the breaker to trip.

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Any corded device such freezer has built-in overload protective devices. The protective device will be protecting you equipment and the cord/plug. The real concern for these application should be overloading the branch circuit and/or the breaker. Since your outlet, feeder and breaker are all rated 20A; then, you will not overload the system. As reminder, the 15A equipment cord & plug are self protected and have internal thermal protection.

Also i like to remind Code section that was posted earlier: "Per the NEC if the receptacle is being wired as dedicated a 15amp receptacle it must be on a 15amp breaker (or fused to 15amps). If it is a dedicated 20amp receptacle then you can have that on a 20amp breaker. If you had multiple 15amp receptacles on one circuit you can then use a 20amp breaker. Same goes for SPST switching devices. All of you "electricians" need to go back and re-read your NEC Article 210 requirements, in particular table 210.21(B)(2) and 210.24, but these are meaningless without the rest of article 210's in depth explanations."

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From my understanding, then it would be wise to use a 15A breaker on this circuit. I'm assuming this is a dedicated circuit too.

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    There's no problem plugging in a device that draws less current than the circuit is rated for, in fact you do it all the time. – Tester101 Jul 23 '14 at 11:00
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Per the NEC if the receptacle is being wired as dedicated a 15amp receptacle it must be on a 15amp breaker (or fused to 15amps). If it is a dedicated 20amp receptacle then you can have that on a 20amp breaker. If you had multiple 15amp receptacles on one circuit you can then use a 20amp breaker. Same goes for SPST switching devices. All of you "electricians" need to go back and re-read your NEC Article 210 requirements, in particular table 210.21(B)(2) and 210.24, but these are meaningless without the rest of article 210's in depth explanations.

Thanks, and please don't give advice unless it is electrical safe, sound, and legal per the NEC, State specifiec revised code's alloted electrical enforment/guieline documents or your local AHJ's requirements

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