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Dick Strauss
03-30-2008, 11:43 PM
Guys and Gals,
I've gotten to the point where my 110V service in the garage just isn't cutting it for my workshop. I want to upgrade my lathe to 2hp but 110V/20A won't do the trick. I'd like to add a 60A panel in the garage for my future power tools needs. My house has a 200A service that has two empty slots. The run from the main to the sub-panel will be just under 100 ft.

Here are a few questions for those folks with more knowledge:

1. I only anticipate about 60A of total demand for the garage. Can I use a 100A sub-panel/breaker in the garage connected to a 60A breaker in the house? The 100A panels are often cheaper ($50) and come with a few breakers (7x20A/110V and 1x30A/220V) as part of the deal. These panels also have a total of 20 spaces instead of just a few. Is this allowed by the NEC so long as the wire is protected upstream by the 60A breaker?

2. I assume that 6/3 is the right size wire for feeding the 60A garage sub-panel, correct? I plan to run both 110V and 220V circuits from this panel. I think I calculated a 3.5% drop using Al 6/3 for 100 ft.

3. I know that aluminum wiring installed 30-40 years ago was problematic because of issues with bad logevity of the connections. What special considerations do I need to worry about today? It looks like the new breakers are designed for dual use (Cu and/or Al). I'm thinking of using aluminum wiring only for the feeder to the sub-panel. I'd prefer to go with copper but have found that copper is quite a bit more expensive.

4. What size EMT would you suggest to get the required fill ratio for the proper temp/current rating and ease of pull (3/4 or 1")?

Any other things I should think to think about other than plan, plan, and plan some more?


Thanks a million in advance,
Dick

Dave MacArthur
03-31-2008, 1:51 AM
Hi Dick,
I just finished installing a subpanel in my garage, much research and reading /questions here. My anwsers:
1. Yes--the lowest CB between the main and sub panel will be controlling. It should be the 60A one in the main panel. The 100A is fine for the sub, that's the same as I did, and for the same reasons as you. Also, you can use the 100A as a main cutoff switch--100A, probably because of their more common use, were cheaper to buy as a replacement if ever needed than a real on/off for 60A.
2. 6 ga wire, 4 of them all the same, is normally shown up to 55 A, but some searching and using THNN will let you get higher. I believe 60A would be fine, but in a quick read of my stuff all the charts I have show 6 ga up to 55A.
3. Caution against dual use--there are quite a few things I've read where dual use devices could ONLY be used with copper now. I would go all copper. The feeder alone might be AL, but you'd have to check the subpanel and main panel connections to see if they are rated for AL wires or if that hmm "violates" their rating. My GE 100A subpanel had "for use with copper wires only" all over it's instructions.
4. I used 1" EMT for my main to sub panel run, and 3/4 " EMT for my circuits from main until they branched out--sometimes 2 12ga circuits in a single 3/4, then after the first junction box where it splits I dropped down to 1/2"emt.


Good luck! By the way, this should really be in the new "Shops" forum, and you should go there and do a SEARCH (this one too), because there are numerous threads on wiring a subpanel. Here is my favorite source, which I recently removed from my signature to comply with the TOS:
http://www.selfhelpandmore.com/homewiringusa/2002/maindwelling/attgarage/index.htm

Steven DeMars
03-31-2008, 2:07 AM
I believe that would be OK. You would actually be using the 100amp breaker as a local disconnect. Your protection for your new run would be the double 60 amp you install in your main 200 amp panel.

You will need to remove the connecting common neutral/ground bar in your new service (sub) panel. You want your ground and neutral for a sub panel to be derived from your main panel.

As to the use of aluminum wire, my suggestion is "no", that may be a knee jerk answer, but if you are doing it yourself, why take a chance. I can tell you this, should you have a fire, whatever the fireman / "fire inspector" deems is the cause is what you are stuck with as far as the insurance adjuster is concerned. Trust me, DIY attracts inspector's attention already, don't get him all excited with aluminum wire . . .

You will need (4) conductors.

Please double check with someone that is "very knowledgeable" on everything . . . :)


Grounding and bonding of the sub-panel
At the sub-panel there must be no connection between the neutral bus bar and the equipment ground bus bar or the neutral bus bar and the sheet metal of the breaker box. If the panel comes with a bonding screw or bonding strap, do not install it to the neutral. Depending on the brand of panel, you may need it to connect the ground bus to the sheet metal enclosure.

By the way, Black and Decker puts out some excellent wiring books.

Rob Will
03-31-2008, 2:19 AM
I would install 2ga copper romex with 4 conductors - and in any area where the romex is exposed, cover it with pvc conduit. You can feed it with a 90A or 100A breaker.

Your power tools and your insurance agent will thank you for installing Copper wire that exceeds your demands. Tools work better, lights dim less.

Rob

Russ Filtz
03-31-2008, 7:23 AM
If you use the 100-amp breaker, be sure and use the proper gauge feeder wire from the main panel (rated for 100A). Don't just assume since the main is 60A you can get away with 60A wire. What if you, or someone who buys the house later, upgrades service?

I used a main lugs panel for my sub. That way there's no question as to what wire gauge the feeder is. It's sized for the breaker in the panel feeding it, not the main panel breaker.

Personally, I would NEVER use aluminum wire in any house, and would not buy a house that had it in there. Too much of a fire hazard.

Matt Meiser
03-31-2008, 8:23 AM
You mentioned EMT--is this a separate garage or attached? EMT shouldn't be buried, and I'm pretty sure it shouldn't be used outdoors at all. Typically what I've seen for a run to another building, is to exit the main building with PVC to the proper depth, then run the cable at the bottom of a trench to PVC running up to the other building.

If you do choose to use aluminum, there is a special grease (I think its a grease--it feels greasy?) for the connections to prevent corrosion.

Peter Quadarella
03-31-2008, 10:31 AM
If the expense is an issue, I would suggest considering less amps. Everyone will always push to get you to do as much current as possible, but a garage really doesn't need as much. I only have 30A service to my garage and have been fine. I really think 40A would be more than enough to run anything that would be needed in a garage (I mean, it's not like you're going to install a 5hp cyclone in a garage setting).

Steven Wilson
03-31-2008, 12:43 PM
I only have 30A service to my garage and have been fine. I really think 40A would be more than enough to run anything that would be needed in a garage (I mean, it's not like you're going to install a 5hp cyclone in a garage setting).

Don't assume that what works for you will work for everyone. A good garage shop can (and many do) have a 4-5HP tablesaw/bandsaw/jointer/planer (take your pick) with a 2-3HP cyclone running and a 3-5HP air compressor that may kick in. 30-40A is a bit low, 60A is a nice choice which should cover most, some will need higher ( as in those who like to play with 3 phase equipment, mills, and such).

Dick Strauss
03-31-2008, 2:47 PM
Dave,
Thanks for the rundown. I wasn't aware of the shops forum. After looking at another chart, I noticed that the ratings depend on the temp rating of the coating and configuration of the wire. I've seen conflicting data on the rating for 6/3 copper and Al.
http://www.cerrowire.com/default.aspx?id=46

Rob and Russ,
2 ga copper for 100A is way out of the question in terms of price and need. Isn't the 60A upstream CB (at the main panel) going to protect the 6/3 wire against someone drawing too much power through the sub-panel in the future?

Russ,
I think Al has a bad reputation from 30 years ago. The problems experienced with Al wiring were for branch circuits only using 10-14ga wire as far as I know. Many of the connections were originally made with steel instead of brass. I think they may figured out what went wrong and corrected it in the NEC.

Matt,
The garage is connected to the house with no opportunity for water infiltration. Thanks for checking...

Steven and Peter,
I think 60A is a good place to start for future-proofing my needs. In the near future I'd only have a 2-3hp lathe and a 2hp BS to feed in addition to misc portable 110V tools (under 1.5hp each). Eventually I'd like to get a 3hp TS, a 2-3hp DC system, a 2hp jointer, 3hp planer.

Thanks for all of your replies. The reason for asking about aluminum is the price difference. I've seen copper priced at more than 7x that of Al. Obviously Al would be worth while, assuming I can do it safely!


Thanks again,
Dick

Rob Russell
04-01-2008, 11:14 AM
Dick,

If you can, run #2 aluminum SER. Think of it as really thick NM-cable (aka "Romex") with aluminum conductors. I think you'll find it's the lowest cost way to supply a 60A subpanel.

Because it's effectively a NM cable, it has to be protected from damage. That means running it along floor joists, although you can attach it directly to the bottom of floor joists - you don't need to run it through holes drilled in the joists. You would not want to just run it along a wall at a height where the cable could be damaged.

When I installed my subpanels, I had the #2 SER running down into the top of the panelboards and that was fine for the inspectors.

Rob

Dick Strauss
04-14-2008, 8:55 PM
Rob,
With a run of 100 ft, the price difference between 6/3 and 2/3 is enough to make me think twice. The flexibility of the 6/3 versus the stiff 2/3 also figures into my decision. The last issue is the larger conduit needed for the 2/3 wire means a higher total project cost. It may be worth it to have 100A service instead of 50A service but I haven't decided yet.

FYI-I checked 100A panel kits and the included breakers. The ones that I looked at are rated for Cu or Al wire.


Thanks,
Dick

Rick Christopherson
04-15-2008, 2:28 AM
I usually stay out of feeder questions because it is not my area of expertise and there are too many factors, but so far, no one has given you an answer to your question without imposing their own desires into your workshop.

You are fine with the #6 aluminum at 90c, and as you have already surmised, there is nothing wrong with using aluminum for your feeder. I don't know if it is still required, but using an anti oxidant compound on the connections is probably a good idea. Aluminum is still the most common conductor for feeders.

Rob Russell
04-15-2008, 7:59 AM
Rob,
With a run of 100 ft, the price difference between 6/3 and 2/3 is enough to make me think twice. The flexibility of the 6/3 versus the stiff 2/3 also figures into my decision. The last issue is the larger conduit needed for the 2/3 wire means a higher total project cost. It may be worth it to have 100A service instead of 50A service but I haven't decided yet.

FYI-I checked 100A panel kits and the included breakers. The ones that I looked at are rated for Cu or Al wire.


Thanks,
Dick

Dick,

2-2-2-4 Aluminum SER is a cable, so you don't run it in conduit. Just install it up high where it will be "protected from damage".

I think you'll find that the 2-2-2-4 Al SER is cheaper than anything in #6 copper, especially if you run individual #6 copper conductors in conduit. That's why I suggested it.

Rob

Rob Russell
04-15-2008, 8:04 AM
You are fine with the #6 aluminum at 90c, and as you have already surmised, there is nothing wrong with using aluminum for your feeder. I don't know if it is still required, but using an anti oxidant compound on the connections is probably a good idea. Aluminum is still the most common conductor for feeders.

Rick - I'm a little surprised! You know that we can't use the 90c column ampacity ratings for normal residential wiring - the circuit breakers only have 75c rated terminals.

It must have been a long day - 2:28AM is late no matter where you are! :D

#6 Al is only good for 50 amps, per the 75c column in Table 310.16.

I agree with using the antioxidant, even if it's not required.

Rob

Matt Robinette
04-15-2008, 8:05 AM
I have used Al wire for the feed it is what the power company uses for the feed to your house. In my area I need to pull a permit for a feed to out buildings and the inspectors have allways been glad to tell me what they expect to see when they come by for the inspection. I can pull 1 permit a year for my own home.

Dick Strauss
04-15-2008, 4:52 PM
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
04-15-2008, 7:46 PM
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
04-16-2008, 10:37 PM
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