Anyone feel like checking my subpanel plans?


Old 08-10-05, 06:35 AM
Thread Starter
Join Date: Jan 2005
Posts: 10
Anyone feel like checking my subpanel plans?

Hi gang. If anyone is so incluned, I'd appreciate an opinion on my plans for a sub panel. I have done lots of branch circuit work, and was initially a little nervous about doing an attached-garage subpanel myself but think it's within my reach. Here is what I am planning, anythng look awry? Much appreciated...

- main panel is 150A square D panel, has some space left
- basement and garage on same level, basement is finished, garage is not
- all basement/garage walls are cinderblock and brick
- garage ceiling is concrete slab
- finished room directly over garage (started out as a porch)

mount panel on plywood on cinderblock garage wall, the wall separating the garage from the finished basement of the house (the firewall)
- box will be 100A rated with 65A main breaker. Looking for 8/16. Any suggestions on model # or where to buy?
- panel will not be covered, and will have approx 5 in. clearance on either side from a door (it will go in the front corner of the garage)

Connect box to main panel
- run wire through finished/unfinished ceiling and hole in firewall, approx 30 feet
- firewall hole will carry wire to main panel as well as one additional nm cable that's part of a three-way switch elsewhere in the house (this will be the only circuit passing through the garage that is not run from the sub panel)
- fill firewall hole with electrician's putty
- breaker in main panel will be 65A single pole
- breaker in sub panel will be 65A single pole
- cable will be AWG 6, 4 conductor (2 hot, 1 ground, 1 neutral). Can I get this rolled into one cable or do I need separate cables?
- break neutral/ground link in the sub panel
- in both panels, connect to both hot bus bars, the neutral bar, and the ground bar

Run branch circuits from sub panel
- one 15A circuit for numerous outlets in the garage, first outlet will be gfci
- one 15A circuit for several outdoor receptacles, first of which will be gfci
- one 15A lighting circuit for overhead flourescent shop lights
- one 15A circuit for receptacles in a finished room above the garage
- may eventually run circuit for heated floor in room above garage (that's why the 65A capacity sub panel)
- all indoor wires will be 12 guage single conductor copper in PVC conduit
- all outdoor wire will be 12/2 copper with ground, underground rated
- may run two indoor circuits in the same section of conduit (six wires in conduit), is that ok?
- will mount all conduit directly to panel, and fixed to cinderblock wall and concrete slab ceiling
- will transition from in-garage conduit to UF cable through to the outside circuits, in pvc boxes covering the hole through to outside

Thanks again for any insight...
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Old 08-10-05, 06:54 AM
Join Date: Jun 2002
Location: Brethren, Mi
Posts: 1,648
Good luck with the 65A breaker, you might find a 60 easier. You dont actually need a main in a sub in an attatched structure, the breaker in the main panel is fine. If you are usig 12 wire there is no point in using 15A breakers, garage circuits should really always be 20A due to motor starts with power tools.
may run two indoor circuits in the same section of conduit (six wires in conduit), is that ok?
You would need only 5 wires, that is an advantage of pipe, you can share ground wires. Personally I like pipe but not plastic for indoor, I like metal, it has a great selection of boxes, fittings, covers etc. You might use smurf tube too?
Old 08-10-05, 07:04 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
65-amp breaker? Might be pretty hard to find. Maybe you mean a 60-amp breaker.

Small SquareD Homeline panels at Home Depot are very reasonably priced. You can even find a package deal that includes some breakers. Finding one with separate grounding and neutral bars already installed will save you the trouble of adding a grounding bar. When in doubt, buy one with more spaces.

You don't need a main breaker in your subpanel. But you can put one there if you want for convenience of shutoff (although it's equally effective to just shut off all the individual breakers, or to shut off the breaker in the main).

5" of clearance on either side of the door is probably not enough. You need 30" side-to-side clearance total, including the panel width.

You can use 6/3 NM-B cable. But the largest breaker you can use on this is 60 amps (but see first paragraph).

I suggest you use 20-amp circuits every place you said 15-amp circuits. Any lighting-only circuit can be 15 amps if you want (Speedy would recommend this because #14 is easier to use, but you may just want to buy a large roll of #12 and avoid having to buy an #14 at all).

If you use NM-B or UF-B cable, I suggest you skip any conduit except where the cable would be exposed and subject to damage. If you use THHN, six wires in one conduit is fine.

Sounds like you've done your homework well.
Old 08-10-05, 08:19 AM
Join Date: Jul 2005
Location: Central Indiana
Posts: 190

- fill firewall hole with electrician's putty
make sure this putty is fire rated to match the rating on your fire wall. probably one hour? And make sure to properly support any cable/conduit runs per NEC. And working clearances around your subpanel may be a problem too as others had already suggested. Good luck!
Old 08-10-05, 01:18 PM
Join Date: Mar 2005
Location: Central Florida
Posts: 149
- breaker in main panel will be 65A single pole
- breaker in sub panel will be 65A single pole

I think you meant 65A 2 Pole breakers instead of single pole?
Old 08-10-05, 07:14 PM
Thread Starter
Join Date: Jan 2005
Posts: 10

Thanks very much all for the opinions. I'll use 60A breakers in the main and sub so I have a single shutoff for the garage, and up all the circuits to 20A. I'll let you know how it goes. Appreciate the feedback.

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