Is there anything in NEC that limits the size of cord with relation to attachment plug?

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mjjstang

Member
Please take it easy on me, not an electrician but mainly work on UL side of things. This seems like it should be easy, but I have not found an answer in my searching. Is there any code in the NEC (I have the 2023) that would limit the size of cord used with an attachment plug? Specifically dealing with 15/20A but to make this easy, I'll throw a ridiculous example, and aside from how ridiculous it is, what actually prevents this from a code perspective, if any? Appliance "widget" has a nameplate rating of 2A and a 18/3 SJOO cord. The attachment plug is a 5-30P (A 5-15P would be the appropriate selection, no doubt). Anything against code here?

Again, I am working in theoretical here to help with some other scenarios. I understand that the main objective here as the NEC is concerned is that the circuit is designed to handle the appliance load (which it is), but my concern is that if the appliance malfunctioned, it's going to take a lot more "malfunction" to trip the 30A breaker, than it would to trip a 15.

Thanks in advance.
 
mjjstang said:
I understand that the main objective here as the NEC is concerned is that the circuit is designed to handle the appliance load (which it is), but my concern is that if the appliance malfunctioned, it's going to take a lot more "malfunction" to trip the 30A breaker, than it would to trip a 15.
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A 30a and a 15a breaker should trip equally quickly with a direct short.

Circuit breakers are not sized to protect every cord size plugged in.
 
CoolWill said:
This would not be an NEC thing. It would be in the listing or product standard.
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Pretty much where I was leaning, but when the standard isn't specific, we tend to check for anything in NEC next. Listing can also allow for some discretion in the case of custom "widgets".

Appreciate the confirmation.
 
There are limits to how large a circuit an appliance can be plugged in to. Don't have the code book handy, but I think you are limited to 150% of nameplate, or a 20A circuits if it is a teeny load. I think it is article 422 where you find this.

So a 2 amp appliance in general should not have a plug larger than 15A, and a 15A receptacle could be on a 20A circuit. Code does allow a 5-30 receptacle on a 15A circuit, so you could use a 5-30 plug if the receptacle had a breaker 20A or smaller which is not a normal circumstance.
 
suemarkp said:
There are limits to how large a circuit an appliance can be plugged in to. Don't have the code book handy, but I think you are limited to 150% of nameplate, or a 20A circuits if it is a teeny load. I think it is article 422 where you find this.

So a 2 amp appliance in general should not have a plug larger than 15A, and a 15A receptacle could be on a 20A circuit. Code does allow a 5-30 receptacle on a 15A circuit, so you could use a 5-30 plug if the receptacle had a breaker 20A or smaller which is not a normal circumstance.
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It’s not really about the cord or outlet, it’s about the protection needed by the load device. CAN you use a 5-30 outlet on a device that is only rated for 2A? Sure, so long as the OCPD ahead of it is whatever the device was listed with (or it has its own internal protection). If you are the OEM of the appliance and you put a 5-15 plug on it when submitting it to UL for listing, UL will assume a maximum 20A OCPD feeding it. But if you put a 5-30 plug on it, UL is going to assume a 30A breaker. So the failure mode in the UL testing of it would have to account for the possible thermal damage curve inherent in the trip curve of a typical 30A OCPD. This is why you see some larger appliances with a listing plate that says words to the effect of “Maximum Over Current Protection…”
 
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