Upstream protection of disconnect

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PhaseShift

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If I have a 100A unfused disconnect must the upstream OCPD feeding this disconnect be sized at no larger then 100A? What if I had a 110A OCPD with a #2 feeder feeding this disconnect? The disconnect is connected to 100A calculated load. What if calcuated load was less than 100A?

On another note is there a requirement in the NEC to label disconnects with the source of their power?
 
augie47

augie47

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I can see a situation where that could cc cur.
A 208v 20HP motor with a FLA of 59.4 could within code be on a 110 amp breaker and a 100 amp NF disconnect is rated for 30HP, so a 100 amp NF would be on a 110 amp breaker.
 
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PhaseShift

Senior Member
augie47 said:
I can see a situation where that could cc cur.
A 208v 20HP motor with a FLA of 59.4 could within code be on a 110 amp breaker and a 100 amp NF disconnect is rated for 30HP, so a 100 amp NF would be on a 110 amp breaker.
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We have an actual arrangemnt in our facility where a 110A breaker is protecting a #2 AWG feeder which is feeding a 100A disconnect. This disconnect is then serving a skid. Is this compliant in this case?

What about labeling disconnects?
 
augie47

augie47

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State Electrical Inspector (Retired)
It appears to me to be a grey area. Unless specifically required to have a higher rating by a specific Code section (such as 424.19, etc), I don't see a problem. (But I may be overlooking something).
As noted, it is permissible with motor operated equipment as long as the switch has adequate HP rating.
Since the NF switch is serving as a disconnecting means and not OCP it would only be rated to carry the load, HP, etc.
 
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