Minimum amperage to studio.

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bobfrost

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Oakland, CA, Alameda Co.
Just completed a small, (480 sqft) studio/guest house. Small bath, basic kitchen. Gas range, heater & water heater. No major heat or motor loads. Supplied it w/ a 40A sub-feed from the 200A main service. On the rough inspection, the inspector approved the 3/4” UG conduit. Now, on the final, he’s insisting on 100A. He admits that it’s not warranted by the connected load, but insists it’s a Code requirement. I’ve asked him for chapter & verse, but he hasn’t gotten back to me yet. Is there anything in the Code that justifies this? Is this a matter of definition? Interpretation? Any ideas?
 
The problem is that if you consider it, as he apparently does, to be a separate residential unit (and it seems to meet the Code definition), then it has to have a minimum 100 "service". The argument can be made that this is not an incoming POCO connection and so the service size requirement does not apply.
If that does not fly, you could remove enough of the cooking facilities that it no longer qualifies as a residential unit.
Take out permanently mounted cooking equipment and substitute a portable microwave and maybe a single burner induction hob that does not have to be there at the time of inspection? Refrigerator, sink, etc. can stay IMHO.
 
225.39(C) requires the feeder disconnecting means to be rated at not less that 100 amps. You could feed a 100 amp main breaker panel with a 40 amp feeder as long as the feeder is protected on the supply end.
 
Minimum amperage to studio.

So it dictates the size of the disconnect, not the conductors. I have an exterior mounted panel on the studio, with a 40A breaker, which then feeds a distribution panel inside, which serves as disconnect for the building. The 40A breaker in the main panel protects the sub-feed. The breaker on studio is only there to serve as a disconnect. If I replace that breaker w/ a 100A breaker haven't I met the letter of the law?
 
curt swartz said:
225.39(C) requires the feeder disconnecting means to be rated at not less that 100 amps. You could feed a 100 amp main breaker panel with a 40 amp feeder as long as the feeder is protected on the supply end.
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That's interesting you would not consider the supply end the 'feeder disconnecting means'?
 
bobfrost said:
... If I replace that breaker w/ a 100A breaker haven't I met the letter of the law?
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No.

The feeder disconnecting means is at the supply end of the feeder at/in the supplying building or structure.

Also, the feeder conductor ampacity must support the OCPD rating. For a 100A OCPD the feeder ampacity must be at least 91A. That is unless you can qualify it under one of the feeder tap rules of 240.21(B).
 
225.6 states that the disconnect can be a"general use switch." The disconnect is not required to protect the feeder. 225.32 states that the location of the disconnect must be "either inside or outside the building or structure served." So, when 225.39 requires that the disconnect for a "one-family dwelling" be 100A, they're not saying that the feeder must supply 100A, only that the switch which serves as a disconnect, at the building served, must be rated at 100A. None of this dictates the size of the feeder.
 
bobfrost said:
225.6 states that the disconnect can be a"general use switch." The disconnect is not required to protect the feeder. 225.32 states that the location of the disconnect must be "either inside or outside the building or structure served." So, when 225.39 requires that the disconnect for a "one-family dwelling" be 100A, they're not saying that the feeder must supply 100A, only that the switch which serves as a disconnect, at the building served, must be rated at 100A. None of this dictates the size of the feeder.
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Sounds reasonable, but you don't have to convince us. ;)
 
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