Electrical ??? for shop sub-panel

[Dick Strauss]

Matt,
The garage is attached to the house. In my case, the feeder is 2/0 or 3/0 copper (yahoo, I'm rich at $4/lb for the copper feeder!).

Rob,
Thanks for your input. The 2/2/2/4 SER is the cable I've been considering but it is 5-6x the price of the 6/3 Al. Does the casing on 2/3 SER cable allow for real protection? I know 2/3 SER Al cable can be buried as is but....? In my case it would be run across the side of the first floor joists accessed via the basement. However, there will be no drop-down ceiling or other protection for the wiring in the basement.

The garage has been finished (sheetrocked). I had planned to run straight from the first floor joists through the wall and into the garage. I'd prefer to have something to protect the cable once in the garage. The cable will run on the outside of the sheetrock. I could cut the drywall out to form a 50' raceway but that gets into too much work to fix the damage. Hmmm...It might be worth the hassle to have it hidden in the wall instead.

Thanks in advance,
Dick

[Rob Russell]

Dick,

2-2-2-4 SER is not direct burial rated, That would be UF (Underground Feeder).

#6 aluminum is only good for a 50A panel - not a 60A panel. If you want 60A, you need either #6 copper or #4 aluminum.

In terms of running the wiring, if you have a cable like 2-2-2-4 SER, you can run it across the bottom of the floor joists in your basement. Once in the garage ... I'd ask your local inspectors what their requirements are. If they will let you run it way up in the top corner where the wall/ceiling meet without conduit, that becomes an easy installation - if you are OK with the looks. If either you're not OK with the looks or the inspectors want the cable enclosed - time to look for an easy raceway to put the cable into.

[Jim Mims]

There is some good advice in this thread.
There is nothing wrong with Al wire. As long as it is installed correctly.
Aluminum got a bad rap because it's rate of expansion and contraction is greater when heated and cooled. Torquing the terminator lug becomes very important. You're also dealing with stranded wire that has space between the strands.
The proper procedure is to tighten the lug to specs. Then work the wire back and forth to squeeze the space from between the strands. Tighten the lug again. Use the panel for a week or two and allow the wiring to heat and cool down a few times, then tighten the lug once again. Then you'll be fine.

Corrosion Inhibitors must be used with Al. No-alux is one brand name.

The advice about separating the grounded and grounding bus bars is correct, as is the use of 4 wires. You don't want multiple grounding paths back to your service, and it's grounding system.

There is a lot of confusion over the 75 degree and 90 degree rating of wire, and it's ampacity. Underwriters Laboratory is very specific about 90 degree ratings. The entire SYSTEM must be rated at 90d. That's the wiring, panel, lugs, breakers, everything. I personally have never seen such an installation. It's best to go with the 75d rating. Many also don't think about derating factors, such as installation in a high ambient temp attic, or multiple current carrying conductors in a conduit that further limit wire ampacity.

NEC Article 240 Overcurrent Protection, allows you to use the next higher current rating of the over-current protective device in certain circumstances. However, 240.4(B) states: "... The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all the following conditions are met:
(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug connected portable loads. ..."
So, #6 Al, at it's 50amp 75d rating must be used with a 50amp breaker. If you want to use a 60amp breaker, #4 Al (rated at 65amp) may be used.

Also, the 4th wire, referred to as the Equipment Grounding Conductor, is sized according to your breaker rating (Table 250.122).
For a 60 amp circuit, you would use #10 Cu or #8 Al.

Most panels that have a main breaker can be bought MLO, or Main Lug Only. See if there is a MLO kit for the panel you want.

Conduit fill:
#6 THW - 3 in 3/4" and 4 in 1" EMT.
#6 THWN - 4 in 3/4" and 7 in 1" EMT.
#4 THW - 3 in 1" and 6 in 1-1/4" EMT.
#4 THWN - 4 in 1" and 7 in 1-1/4" EMT.

I would use #6 Al, on a 50 amp breaker, in a 1" conduit.

- Jim