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Calculations / Engineering30 amp receptacle/ 20 amp breaker.
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Posts:630 amp receptacle/ 20 amp breaker
Where I work there's two rated 30 amp receptacles and two 20 amp receptacles on one 208 VAC /20 amp breaker. I was told by senior mechanics that because the circuit's wired with 10 AWG and only one milling machine is used at any given time it's acceptable. None of the machines can draw 30 amps but some have the 30A plugs for whatever reason put there by mechanics who already retired. The code book (in my understanding) states that a 30A receptacle can only be wired to a 30A breaker. This to me means it cannot be wired to a 20A breaker. Am I missing something here? Suggestions were made to change plugs or use adaptors and remove the 30A receptacles. Or we could rewire another separate 30A circuit for the 30A receptacles or change the circuit to 30A with a 20A disconnect to the 20A receptacles. Some say leave it as is and it's not against code. Thanks in advance for any input. .
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07-05-10 04:31 AM #2 augie47
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Posts:10,618Welcome to the Forum.
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As best I can tell, there is no Code violation in what you have. It is a violation to have a single receptacle on a oversized breaker, but, IMHO, no violation in receptacles being oversized.
I have seen such in heavy use environments to gain the advantage of a heavier receptacle/plug.
I'm so old when I go out to eat they ask me to pay in advance .
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07-05-10 12:16 PM #3 Bob Magee
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Posts:6Thanks for the response. So then my question would be can we go to a 40A or 50A receptacle on the same breaker if we do not need to "conform" as the code book asks? I realize common sense should be used, but depending on who your working with different interpretations of code and common sense could be dangerous. For an example I wouldn't want to be an outside contractor, which we use sometimes, trying to accomplish a task and following a code book assuming that this 30A receptacle needed for his own servicing equipment is on a 30A breaker, even if the worst that happens is he keeps tripping the breaker. Or maybe we get a machine that will use 30A a year from now and we forget that it's a 20A breaker. Also I don't see where the code book OK's it. I guess that's my real question. Thanks again. .
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07-05-10 12:42 PM #4 Dennis Alwon
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Posts:23,465Bob if it is a single recep. the code states in art. 210.21(B)(1) that the recep. be not less than that of the branch circuit. It does not limit us as does T.21021(B)(3) which is applicable for a circuit with more than one receptacle.
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07-05-10 12:50 PM #5 augie47
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Posts:10,618It's not necessarily a good idea and, since there is more than one receptacle on the circuit, one could read 210.21(B)(3) to state that on a 20 amp circuit, receptacle ratings should be 15 or 20 amp per Table 210.21(B)(3).
However, when you read 210.21(B)(1) you find the only limitation is that the receptacle can not be rated less than the branch circuit.. but that is for individual receptacles.
From a "safety" standpoint I can see no concern as there is no overload.
And, as stated, I have seen oversized receptacles/plug employed to provide a "heavy duty" configuration for often used pieces of equipment.
As noted, it may literally be a violation of 210.12(B)(3)
(sorry Dennis...walked on you)
I'm so old when I go out to eat they ask me to pay in advance .
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07-05-10 03:19 PM #6 Dennis Alwon
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Posts:23,465 Originally Posted by augie47
(sorry Dennis...walked on you)
I looked at it as you supported my viewpoint.
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07-05-10 10:01 PM #7 Bob Magee
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Posts:6 30 amp receptacle/ 20 amp breaker
Thanks Dennis and Augie for the input. I knew there was no danger of overload but I wanted to be sure we were within code. I also wouldn't want someone to stretch the code to work for themselves on another system since the rules are sort of bent here. You folks were quick to respond and answer some questions. Thanks. I'm more comfortable with it now. As stated there are two 20A and two 30A on the same three phase circuit so we'll be changing to a 30A breaker since we have the 10AWG but using 20A disconnect boxes for just the 20A receptacles. This should keep everyone happy. Thanks again. .
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