Maximum Current for Experimental Equipment on Existing Branch Circuit

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Hello, I'm trying to clarify the maximum allowable load for a piece of equipment that will be used for an experiment next month. We're looking to connect a chiller, with an 18A rating on 115V service, to an existing unused 20A circuit with 20A receptacles.  For reasons unrelated to the chiller, it isn't able to run for more than an hour per day, so I'm pretty sure that the 80-percent rule wouldn't apply. Even if it does (or if for some reason we're forced to treat it as a continuous load), do any of these thoughts make sense:
  • Since the operation of the equipment is temporary in support of a test, and no other loads will be connected to the circuit while it is there, we should be able to make use of up to 20A of a 20A branch circuit, with a 20A receptacle.
  • A circuit containing multiple 20A receptacles can (or should) have a 25A breaker if the wire supports it.
  • NEC would apply to the installation of receptacles, based on anticipated loads. If the equipment is UL-listed, and requires less than 20A, it just needs to be plugged in to a circuit that can supply 20A.
Hopefully i'm not too far out in left field here--any pointers on where I'm wrong would be greatly appreciated. Thanks!
 
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charlie b

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I agree with everything except your second bullet. You can't put 20 amp receptacles on a 25 amp circuit. Reference 210.21(B)(3).

Welcome to the forum.

By the way, you might want to revisit your choice of software for typing into this forum. You had a lot of <br> and   coding in your text. I removed it.
 
Charles,

Thanks for the help. Good point on the 25A breaker--I guess the code essentially assumes that 20A receptacles will always support 15A plugs (or the rationale for margin with multiple 15A receptacle circuits is different from 20A receptacles).

I think the extra formatting stuff crept in when I lost my internet connection in the middle of posting--I neglected to preview before posting to see if it got fixed. I'm not using anything other than the standard interface in a browser--sorry for the added hassle.

Thanks again!

David
 

mbrooke

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I see no problem in it. From a code perspective the only issue would be running it for more than 3 hours as the 80 percent rule would apply.


In the real world its not uncommon to find circuits loaded to the max beyond 3 hours. I have done services in restaurants where dozens of 20 amp circuits were pulling 20, 22 even 26 amps 16 hours at a time for years. Techinically not code compliant and certainly poor design but a 20 amp loaded to 20 amps will not cause a fire. If the system is properly disigned there would be no danger.
 
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