Replacing conduit and panel in studio

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Old 07-29-19, 07:29 AM
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Replacing conduit and panel in studio

My brother has a place with an outbuilding that probably formerly was a guest or workers house, now he uses as a place to do artwork or read and write (as a hobby). Iíll call it a studio. The main house and studio were built sometime in the Ď40s. Due to tree roots, he has had to dig up the entire iron sewer line which goes from the studio to the main house. In the process, he found the conduit completely rusted out, and needs to be replaced. The subpanel in the studio also needs to be replaced because it has been problematic for a while, and is a mess.

I plan to help him with the electrical, and have a few questions I could not clarify reading previous posts here. The ~100 foot conduit contains three 8 gauge wires feeding the subpanel (no ground), and two more 12 gauge wires feeding outdoor flood lights, which are controlled by a switch at the main house. In the studio, there is a tiny kitchenette with a sink and a small electric 4 burner stove with oven, and a mini fridge. There is also a bath room with a small (25 gal?) electric water heater. There is no heating in the studio except for the occasional use of a portable 1000W heater.

The breaker on the main house feeding the subpanel is 60 amps. Does the breaker and wire size seem adequate? We could upsize if recommended. Also, we would add a fourth wire for a ground in the new PVC conduit.

The extra two wires in the prior conduit for the outside lighting seem contrary to code. Should those be placed in a separate conduit if still switched at the main house?

Thanks in advance for any information you can provide.
 
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07-29-19, 08:31 AM
ibpooks
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The existing installation is over-fused; #8 copper should not exceed 50A. With kitchen facilities in the outbuilding, I think this feeder is too small.

My recommendation would be to increase the service size, and there are two things to consider. First is a "demand load calculation", which you can find walkthroughs online to do it. This gives you the minimum service size for the building by the electrical code. Second, if this is an inspected job you need to ask the inspector if this guesthouse is considered a "dwelling unit". If so minimum service size is automatically 100A. If the city does not consider it a dwelling unit, then you can use calculated load to size the feeder.

Switched outdoor lighting wires are allowed in the same conduit as the building feeder, but the lighting circuit should be powered from the outbuilding panel, not the main building panel.
 
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Old 07-29-19, 08:31 AM
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The existing installation is over-fused; #8 copper should not exceed 50A. With kitchen facilities in the outbuilding, I think this feeder is too small.

My recommendation would be to increase the service size, and there are two things to consider. First is a "demand load calculation", which you can find walkthroughs online to do it. This gives you the minimum service size for the building by the electrical code. Second, if this is an inspected job you need to ask the inspector if this guesthouse is considered a "dwelling unit". If so minimum service size is automatically 100A. If the city does not consider it a dwelling unit, then you can use calculated load to size the feeder.

Switched outdoor lighting wires are allowed in the same conduit as the building feeder, but the lighting circuit should be powered from the outbuilding panel, not the main building panel.
 
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Old 07-29-19, 12:09 PM
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Thank you Ben for you quick and thorough response and recommendations. I will look for and do the demand load calculation and see what he wants to do from there. A permit has been received for the sewer work, but the electrical was an unpleasant recent surprise. I'm afraid he opened Pandora's box when he started the excavation. This begs another question: Is it likely that an electrical inspector will require any other upgrades to the electrical system if the conduit and panel is changed and upgraded? If so, I will beg off this and tell my brother it is beyond my level of competence (meaning he will have to hire an electrician). Thanks again.
 
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Old 07-29-19, 12:28 PM
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He will require four wires which you know. He will require a ground rod at the studio
 
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Old 07-29-19, 12:38 PM
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Permits and inspections are always regulated at the local level, so we can't say exactly what your city/county will require. In most jurisdictions a homeowner can pull an electrical permit with the scope of work listed. The inspector generally will only look at the work listed in the permit. Some cities may impose additional requirements, but they should be upfront with those when you file the permit.
 
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Old 07-29-19, 06:48 PM
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We will be doing some homework, then have to make a decision about the path forward. One way or another, your recommendations will be incorporated. Thanks again to both of you for your responses, and thanks for your time. What a great forum.

Jim
 
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