Mother in law apartment - Circuits and Sub Panel Size

Old 11-20-10, 09:06 AM
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Mother in law apartment - Circuits and Sub Panel Size

I have gutted and in the process of rebuilding a 650 SF basement mother-in-law apartment and will be adding a sub-panel to it as part of the project. I am planning on providing the following circuits:

Bathroom 1-20 amp GFI
Lighting 1 - 20 amp ARC fault
Kitchen counter 2-20 amp GFI
General use receptacles 1-20 amp ARC fault
Fridge 1-20 amp
Range 1-40 amp
Microwave/exhaust 1 20 amp

I have a 40 ft run from the main panel and plan to use a 60 AMP breaker at the main with #6 hot and neutral and #10 ground.

My questions:
Is the 60 Amp main the correct size?
Is the wire size of the run to the sub panel correct?
Does the sub-panel need to have a disconnect for the whole panel or will the individual circuit breakers be adequate?

If I decide to add a 35 amp dryer circuit, will I need to go to a 75 Amp breaker and larger feed wire?

Thanks for any assistance.

David J
Old 11-20-10, 10:12 AM
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I would strongly advise that you have two 15 ampere lighting circuits rather than a single 20 ampere circuit. The reason is that if for some reason the single circuit were to trip the circuit breaker you would be in the dark whereas with two circuits you would always have some lighting available.

Clothes dryer circuits are 30 ampere, not 35 ampere.

I think that 60 amperes could be a bit small if the range were cooking a large meal with the microwave oven going along with several lights (and maybe a TV) and it would definitely be small if the clothes dryer were also running. Going to #4 type NM cable would allow you to go to 70 amperes and if you ran #4 type THHN individual conductors through conduit you could go to an 80 ampere circuit. Both of these options would require going to a 100 ampere sub-panel rather than the 60 ampere model. Using a main breaker larger than 60 amperes (up to and including 100 amperes) requires a #8 equipment grounding conductor. All wire sizes are for copper conductors. The sub-panel does not need a main circuit breaker in this instance.
Old 11-20-10, 05:09 PM
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#4 THHN in conduit will allow you to go to 90 amps. Or you could go #3 NM-B for the same 90 amps. Other than that Furd's suggestions are spot on.
Old 11-21-10, 01:56 PM
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Thanks for the responses guys. I will follow Furd's recommendations.


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