Sub Panel Questions

I am planning to set up a sub panel in my mother's garage. The house has a 125Amp service panel with spare space to put a breaker. The 21' x 22' garage is mostly detached but the roofs of the two structures connect via a dog trot (15 feet long by 8 feet wide) with an enclosed ceiling. The service panel is on the exterior of the building. The circuits my mother needs to set up the garage as an art studio are: one lighting circuit for 6 dual-bulb, 4-foot flourescent fixtures, one electrical recepticles circuit, one circuit for sprinkler control and two dedicated circuits for a couple of small split pack AC units. The cable path distance from the service panel to the proposed sub panel location is approximaely 100 feet.

My plan is to set up a lug panel with 8 spaces in the garage, feed it with a 60A breaker from the service panel, use NM-B 6/3 cable and run the cable up into the attic and over to the sub panel in the garage.

I've read a lot of good information on sub panels on this forum but still have a few questions about this specific installation:

1) The service panel is surface mounted on the brick on the outside wall of the house. the hole in the brick where all the branch circuits are run into the house is pretty full. Can I run the cable feeding the sub panel up from the service panel in conduit on the outside of the building through the roof soffit above and then stapled in the attic the rest of the way to the sub panel in the garage?

2) I consider the garage to be detached but it is connected to the house using the same roof. Does this application need a separage ground rod?

3) The split pack A/C units are pretty small and only need a 15A 110VAC circuit each. Can I just provide them each with an fused or unfused 30A disconnect (smallest I find). If fused, I can change the fuses to 15A.

4) If I use one of these disconnects, since they are for a 220VAC circuit, do I only break the one hot leg or do I also break the neutral through the disconnect?

Thanks for any advice on this.

 

You cannot run NMB cable in conduit on the exterior of a building.

300.9 Raceways in Wet Locations Abovegrade. Where
raceways are installed in wet locations abovegrade, the interior
of these raceways shall be considered to be a wet location.
310.8(C) Lists the insulations allowed in wet locations.
334.12(B) NM cable cannot be used in damp or wet locations.

You need to install your EMT from the panel to the attic and use #6THWN-CU conductors 2-Blk 1-White ( need to buy the #6 neutral with white insulation) only conductors larger than #6 can be identified using white tape(200.6) You can install a NEMA-1 junction box in the attic and splice you single-conductors to you NMB cable conductors. The EMT can serve as the ground up to the J-Box but you need to bond the ground conductor in you cable to the J-Box.

 

Do you have attic space all the way to the garage? If you do, you can rum NM-B cable through it, but if you don't, NM-B cable cannot be run exposed outside. Even exposed under the roof would be considered a damp location and not suitable for NM-B cable.

 

In most cases, yes. That's considered a sleeve. Since it's outside, though, you need to install individual THWN conductors, as bahtah noted, to get from the panel to a junction box in the attic, and splice to the NM-B there. If you use a metal box to do that, remember to bond it to ground.

Since the breezeway has a ceiling, I'd say that you're good to use NM-B from the attic to the garage subpanel, but ask your local jurisdiction - your inspector - to be sure.

Good question. Again, ask your local jurisdiction for their interpretation.

Since you're feeding each unit with 120V (not 110V) hot-to-neutral power, you can use a regular, on/off 20 amp toggle switch - horse power rated - as a service disconnect for each one.

Only the hot leg. I can think of only one instance where neutral needs to be switched, and that has nothing to do with the project you're doing.

 

Thanks to all - this is great information.

bahtah - I was going to use rigid rather than EMT since it was outside exposed and only a small straight vertical run. If I can use EMT outside it would be easier. Thanks for the information about how to keep this within NEC.

CasualJoe - There is attic space all the way to the garage. The dog trot connecting the house to the garage is about 8' wide by 15' long and it is an enclosed roof so makes a small attic crawl space connection to the garage.

Nashkat - Thanks, I searching the permit process online now. It's in Harris County, Texas and their site does not make it easy. I'll probably call and speak to someone in the permits office.

 

If you use EMT outside be sure to use compression fittings, not setscrew fittings.

Run one 3 wire cable (14/3) and install a 2 pole 15 amp breaker. This will give you the 2 - 120 volt, 15 amp circuits you need for the A/C units. The two circuits will share the neutral.

 

It's probably set up for professional contractors, since that's 99.9% of their business.

How will you get from the top of the vertical run into the J-box where the individual conductors can be spliced to the conductors in the cable?

 

County or city? If Houston a permit must be pulled and only a master electrician can pull the permit. I'm not familiar with Pasadena but I do recall they have strict code enforcement. If county there is very little inspection.

 

Apologies for the delay in responding. I am working on the framing to get the garage setup to turn into an art studio. It was easier framing and remodeling when I was a kid than now in my 50's. Good chance to teach my kids a little about building though.

Thanks again for the help. I'm getting closer to the point I want to do the electrical. In answer to your questions:

It is Harris County but outside of the city of Houston to the North. Cypress area north of FM 1960. Whether or not they do much inspection in Harris County, do you know if a home owner can pull a permit from the county?

It has a hip roof with a relatively steep pitch. It looks like I can use a 45-degree sweep on the conduit as it enters through the soffit and then extend into a box fastened to a rafter


Thanks for the suggestion. In this particular case, my mother plans to put these two split packs on either side of the back wall so they will probably be separated about 18 feet apart. I will likely use the horsepower rated 20A switch idea that Nashkat1 suggested

I've spliced cables in juntion boxes before, but never a feed to a panel. What are the options for the splices and the best methods.

Thanks again for all the help.

 

The easiest would be a typical wire/wing nut. Buchanan has a WT54 blue wing connector that will accept two #6s.

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