I have a piece of equipment that will only run at 50% value, but it's spec tag shows 109A. Since I know the actual load it will ever run under, can I size the breaker for 100A? NEC shows lots of exceptions for oversizing your breaker but can I make an exception to undersize the breaker if I know actual field use will only be 50%?
Sizing load for a piece of equipment
- Thread starter dabatman
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- Lockport, IL
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- Semi-Retired Electrical Engineer
You can use a 20 amp breaker, if you like. I should mention that the owner might not like, but happy owners is not an NEC concern. All of the sizing requirements for overcurrent devices are written in the sense of "not more than." But you can over-protect at will.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
It also depends on the nature of the equipment. If it has AC motors or transformers in it, your OCPD must be capable of holding in under normal starting current conditions. Under sizing the breaker may get you into trouble with nuisance tripping.
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- Massachusetts
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- Lockport, IL
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- Semi-Retired Electrical Engineer
I am. Those articles talk about the wire size, not the breaker rating. :wink:
I believe that if I had a calculated load of 30 amps, I could use a #10 THHN conductor, and a 5 amp fuse, and not violate the NEC.
You must size the wire to the load then, correct?
You must size the wire to the load then, correct?
In turn then, I still need to size my wire for actual load and not the breaker? Even though I'm saying that my actual load is 60A but the spec tag is 109A, then I would still need #2 wire on my breaker for a non-continuous load.
You must size the wire to the load then, correct?
In turn then, I still need to size my wire for actual load and not the breaker? Even though I'm saying that my actual load is 60A but the spec tag is 109A, then I would still need #2 wire on my breaker for a non-continuous load.
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