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Lil Volt · Nov 15, 2007, 08:30 PM

I have a separate small living quarters that is a single room that is about 180 feet away from the main panel. It is going to get another little bed room a small kitchen and a bathroom also maybe a washer. The main panel is a 100 amp meter socket combo. What should I upsize the main panel to? What size feeders do I need to the sub panel and what size subpanel should I get? Do you need to bond the main panel to the sub panel and still pound a ground rod? Isolate the nuetrals? Thanks

Cobraguy · Nov 16, 2007, 05:21 AM

Each area of the country can have different little quirks in the code. A call to your AHJ would help prior to planning this project. I would take a good hard look at the NEC prior to laying out your plans. There are requirements for receptacle locations in the kitchen, bathroom, walls, etc. Some must be dedicated, some must be a certain size. In this case, if you're not totally comfortable with code requirements, it might be a good move to hire someone to at least do your plan for you and figure your load calculation. You very well may need to upgrade your main panel too.

A sub panel has the neutrals and grounds isolated. If the structure is not attached to the main house, usually ground rod(s) are required. But don't take my word for all this. I would wait for, or contact, a professional who is intimately familiar with NEC... and probably NEC 2008. For example, if this can be considered new construction from the remodel, you may have to upgrade to AFCI's too.

tkrussell · Nov 16, 2007, 06:00 AM

Any panelboard in any separate building fed by a main panel in another building on the property must be grounded using ground rods or metal water lines if available.

Do not refer to the NEC 2008 edition until your state adopts it into law.

Calculating service and feeder sizes is a bit involved, must be done according to NEC Article 220.

The 180 foot distance will also involve voltage drop calculations to size the feeder conductor for the connected load, distance and wire material.
You can find a link to the actual NEC 2005 code in the Read this First sticky note at the top of the Electrical forum.

I agree with Cobra to contact the AHJ, Authority Having Jurisdiction, which is the legal term for that person or entity that performs electrical inspections in your area. This may be an electrical inspector, or Fire Marshall, building inspector, or a third party firm. New York State, for example, uses private firms certified by the state.

Cobraguy · Nov 16, 2007, 06:10 AM

Thanks tkrussell. I thought the 2008 code was adopted automatically on 1/1/08. My mistake. However, I still think it's entirely possible he may be required to have AFCI's for the bedrooms in this case. Agree?

tkrussell · Nov 16, 2007, 07:23 AM

As you mentioned only if there is a remodel and complete rewiring of the bedrooms. AFCI is not required for existing installations just because of a new service or an upgrade.

The code must be adopted by the Legislature in each state, or however that state handles building codes.

Some states may even be using the 2002 or even the 1999 code still to this day.

Lil Volt · Nov 16, 2007, 04:52 PM

Thanks guys for the help. I just still had one question about bonding. So you pound a ground rod for the sub panel but do you still carry the ground from the main panel and bond it to the sub panel?

tkrussell · Nov 17, 2007, 05:33 AM

Yes, absolutely.