Sub panel size and feeder wire size

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  #1  
Old 04-24-10, 10:01 AM
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Sub panel size and feeder wire size

I am renovating an accesory dwelling unit in my home and will be installing a sub-panel to serve it. I am looking at providing the following circuits:

range 1-30 amp
small appliance 2-20amp
bathroom 1-20 amp
bedroom 1-20 amp arc-fault
other lighting 1-20 amp
other general 1-20 amp

I don't want to add more than necessary since it is a small space (500 SF).

My plan is to use a 60 amp breaker at the main and run #6 THHN (2-hots, 1 neutral) and #8 ground in counduit betwenn the main and sub (about 25 feet).

Does this make sense or am I missing something.

Thanks for the help.

DavidJ
 
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Old 04-24-10, 10:11 AM
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Most ranges require a 40 or 50 amp circuit, is this some type of a smaller apartment sized electric range? What about heating, cooling and water heating, any electrical requirements there? By the term "accessory dwelling", do you mean this unit is inside your house or is it detached? The items you list can more than adequately be served with a 60 amp subpanel.
 
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Old 04-24-10, 01:08 PM
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It's been more than ten years since I have had any dealings inside Seattle city limits but I'm pretty sure you will find that all general purpose 120 volt circuits need to have AFCI protection.
 
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Old 04-24-10, 03:30 PM
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The accessory dwelling unit (mother-in-law apartment) is inside my house and heat/water power needs are already provided for.

I know Seattle aropted the 2008 NEC. Are AFCI's required on all 120 circuits except kitchen counter appliance circuits and the bathroom? I has thought they were just required for bedrooms.

Thanksf or the info.

DavidJ
 
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Old 04-25-10, 06:11 AM
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The 2008 NEC has expanded the use of AFCI protection to most ares of the house except for the kitchens and bath areas.

 

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Old 04-25-10, 08:48 AM
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To repeat CasualJoe's question are you sure 30a is enough for a kitchen range. Even if the planed range will work on a 30a circuit planing ahead for a possibly larger stove seems prudent. Yes, I know even a full size range will in normal use draw less then 30a but circuit sizing should be based on what it could occasionally draw with that turkey in the oven and all four burners in use.
 
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Old 04-25-10, 11:26 AM
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I will plan on a 50 amp breaker for the range. With that, my circuits are as follows:

range 1-50 amp
small appliance 2-20amp GFI
bathroom 1-20 amp GFI
bedroom 1-20 amp AFCI
other lighting 1-20 amp AFCI
other general 1-20 amp AFCI

Does a 60 amp breaker at the main and #6 THHN (2-hots, 1 neutral) and #8 ground in counduit between the main and sub (about 25 feet) still make sense or should I step it up to 75 amps.

Thanks for the previous responses.

DavidJ
 
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Old 04-25-10, 11:58 AM
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Not a pro but I would stay with the 60a breaker but bump the hots and neutral to #4 that way you could easily up grade breaker size if you needed to later. Wait for a pro to give an official answer though. Of course if you are using conduit you could also pull larger wire later if needed.
 
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Old 04-25-10, 03:42 PM
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I'd stick with the 60 ampere feeder because the next size up in panelboards is 100 ampere and that would require no less than #3 conductors. Remember that for many years 60 ampere service was the standard.

Remember also that the kitchen range is a 240/120 volt appliance so it requires a 2-pole circuit breaker. For a MIL apartment I see no reason to have anything larger than a 40 ampere circuit and you would be wise to pick out the range BEFORE making any decisions as to the size circuit required.

I would strongly suggest that you break up the lighting into at least two separate circuits, this way if the circuit breaker trips the apartment won't be in total darkness. The same is true of general-purpose receptacles, two circuits. I would make the lighting circuits 15 ampere and the GP receptacles could be either 15 or 20 depending on whether or not you expect any space heaters to be used.

I like to keep receptacles and fixed lighting circuits separate although there is no code requirement to do so. At least spread out the circuits so that a single area is NOT all on one circuit.
 
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Old 04-25-10, 04:01 PM
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Thanks for the input. I will go with the 60 amp panel and definently have the range selected before derterming its circuit size. I also like to separate lighting and receptical circuits but don't want to overdue it with the price of AFCI breakers.

DavidJ
 
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