Sub panel wire requirements- need some edumacation

[Parke]

Hello all, this is my first post to this forum. I've been having a blast reading threads and looking at pictures, but i must get down to business.

I'm currently redoing the house one room at a time, while sneaking in some garage improvements when and where I can while keeping the boss happy. I also have my dream 25 x 36 detached garage project which is at least a couple of years down the road. I have finally delved into Sketch Up and I've got a nice 3D (but still very basic) rendering of it now, which I will post when I learn the file management and forum rules.

In the mean time, I need to install a subpanel in the garage as the garage and the master bedroom/bath (upstairs) are on the same circuit! Running the table saw or the air compressor results in popping the fuse everytime someone is running the vacuum or something upstairs. Aaaaaargh. The plan is to rewire the garage as a fully functional woodshop for now, and eventually run power from that subpanel to the detached garage which would become a real workshop. I have a contact who is a union shop electrician to do the panel work/hookups etc. But first, I'd like to figure out what all is involved.

Specifics: The main panel is on the southeast corner of the house. The garage subpanel will be on the northeast corner. I figure that I will run cable up the east wall to the attic, around the perimeter of the attic and then back down the north wall to the garage. The run is about 96 feet. I have 200 amp service in the main panel with three adjacent empty slots. I am thinking of a 100 amp subpanel in the garage. I am replacing drywall as I do rooms as the insulation is circa 1973 and essentially nonexistant. So the drywall/mudding work involved is a non-issue as it is the main panel's room's turn now.

Garage power needs are :
lighting (600 sqft) (Refurbish),
2- 20 amp circuits for receptacles (new),
2 garage door openers (exisiting but powered by extension cords to two of the three existing outlets, sigh,
a 240 volt, 30 amp electric heater (new).

Equipment that I run are basic woodworking with mostly 1 hp motors: tablesaw, tile saw, 12 in miter saw, drill press, plus a 1.8 hp peak air compressor and a 3 1/4 hp router, a 2 1/4 hp peak planar, and a saw dust collection unit. It's just me in the garage, so only one tool at a time, but the heater will be on in the winter, plus the dust collector from time to time. I do not see ever (famous last words) a welder, or any other 240 volt equipment.

So, questions: Is 100 amp fr the subpanel overkill? Is there multistrand cable big enough to run 100 feet or so (e.g. 4-3)? Do I use single strand, and if so are there conduit requirements? And lastly, I don't like the idea of aluminum, and I realize copper is awfully expensive, but I think I'd sleep better with copper.

Thanks!

 

[pottsie454]

There is nothing wrong with aluminum for sub panel feed as long as you terminate it correctly and use deox.

 

[pattenp]

Use aluminum SER. No conduit is needed in most cases. I think a 100A sub is fine, do you really need 100A, probably not.

I would use a 100A main breaker panel for the sub-panel and feed it with 2-2-2-4 Al SER. Protect it with up to a 80A breaker in the main panel. You'll be good to go. You can push the #2 Al SER to 90A if the cable is not run within insulation.

Edit: I forgot you said in the future you would like to run a sub-panel in a detached garage from from the sub-panel in the attached garage. You may want to do the full 100A using Al 1/0-1/0-1/0-2 to the attached garage.

 

[Aceman]

How many feet of cable would be installed in insulation?

 

[G_P]

I have heard wire coathangers work well in this situation.

http://www.garagejournal.com/forum/showthread.php?t=178972

sent from the toilet via tapatalk 2.

 

[wyliesdiesels]

I have heard wire coathangers work well in this situation.

http://www.garagejournal.com/forum/showthread.php?t=178972

sent from the toilet via tapatalk 2.

Ahhahahah! LMAO

 

[dimarcelli]

2/3 nm copper would run you some serious coin for 96 feet. I think last time i checked my supply house was selling it for like $8.70 / foot. 1-1-1-3 aluminum se is much cheaper, around $2.50 / foot.

 

[theoldwizard1]

Are you really certain about that electric heater ? They are expensive to operate and without it, you could probably get by with a 60A panel.

 

[Falcon67]

I have heard wire coathangers work well in this situation.

http://www.garagejournal.com/forum/showthread.php?t=178972

sent from the toilet via tapatalk 2.

I think for 100A you'd need special twisted pair coathangers.

I used 2-2-2-4 AL SER/USE-2 cable for my shop. The run is about 120' and I went straight across the attic, just suspended the cable above the insulation. I use a 70A breaker on mine because it was in stock at HD. I have a lot of equipment at horsepowers like and below what you listed. I seriously doubt that I'd ever trip the 70. The shop panel is a 100A 20 slot unit with a main. Handy to have a disconnect at the shop end of the run.

From what you list for doing in the house garage, I would put a 100A 6 or 8 slot panel in the garage. That gives you room for a 240V heater circuit and a couple of other 120V runs. Your garage doors and general use outlets ought to be using the main house panel anyway, but if not you could feed them from there. Leave a couple of slots for the breaker to the eventual detached shop and you'll be set.

 

[Stuart in MN]

You should mention where you live...are you in the US, and if so what state? It can affect the advice you get.

Also, you mentioned running the wire up to the attic, then over and down to the garage - is this a single story home w/no basement?

 

[Parke]

Hi all, and thanks for all the responses.

From other posts I have noted that aluminum is more of a concern for small diameter wire, like 14 ga, so I feel a bit better than that.

The house is a raised ranch in northwestern New Jesery, no basement. So, the wire will have to fed through insulated exterior upstairs walls, call it 16 feet, plus any first floor insulation in the stud bay where the main panel resides. I havent removed the panel cover yet, but I'm guessing there isn't much insulation in that space with all the wires connecting to the panel. The garage wall is not insulated.

The garage temps are in the low to mid 40's this week. It really limits my working time to an hour or so, so yes the heater is desired and needed. I'm looking at a 5,000 watt model that has gotten good reviews. I'm only looking to get the garage temp up to 60 degrees tops.

From patenp: "Edit: I forgot you said in the future you would like to run a sub-panel in a detached garage from from the sub-panel in the attached garage. You may want to do the full 100A using Al 1/0-1/0-1/0-2 to the attached garage. "

This isn't clear to me, would I still run the 2-2-2-4 Al SER from the main panel to the garage subpanel, and then the Al 1/0-1/0-1/0-2 from the garage sub panel to the detached garage? The run to the detached garage will be about 70 feet. Also, when (and if) the detached garage gets built, the power requirements for the garage will drop substantially to lighting, garage door openers, and the occasional outlet plug.

I looked up the cost of 2-2-2-4 Al SER on HD after the first few responses, $775 or so for 500 feet, or about $1.50 per foot in bulk, far far more affordable than copper, and another reason to get more comfortable with copper.

My reference books mention that one can run wire across the top of attic joists if its braced with 1x 4's. But the attic insulation has been boosted, and the above posts indicate that burying loaded service cable in insulation is bad practice, so either I am building an electrical viaduct running oabove the joists, or else can I staple the service cable to the rafters, as close to the eaves as possible?

Thanks again for the info.

 

[Parke]

Thank you for the link, very edumacational.

Re: So in theory you're going to need to run more than one coat hanger. Try 6 or 7 of them together.

I think that's what we've got heating the oven. Is this also a no-no to run in insulated walls?

 

[pattenp]

...l

From patenp: "Edit: I forgot you said in the future you would like to run a sub-panel in a detached garage from from the sub-panel in the attached garage. You may want to do the full 100A using Al 1/0-1/0-1/0-2 to the attached garage. "

This isn't clear to me, would I still run the 2-2-2-4 Al SER from the main panel to the garage subpanel, and then the Al 1/0-1/0-1/0-2 from the garage sub panel to the detached garage? The run to the detached garage will be about 70 feet. Also, when (and if) the detached garage gets built, the power requirements for the garage will drop substantially to lighting, garage door openers, and the occasional outlet plug.


My reference books mention that one can run wire across the top of attic joists if its braced with 1x 4's. But the attic insulation has been boosted, and the above posts indicate that burying loaded service cable in insulation is bad practice, so either I am building an electrical viaduct running oabove the joists, or else can I staple the service cable to the rafters, as close to the eaves as possible?

Thanks again for the info.

I was suggesting the power feed to the attached garage from the main panel be the full 100A using the #1/0. The feed to the detached garage could then be the #2. You don't want to feed the detached garage with a higher amp feed than the sub-panel in the attached garage is fed with. Also the SER can run within the insulation, it just needs to be sized from the 60C degree column and #1/0 Al is fine for 100A at 60C. You could feed both subs with #2 if you want.

The running boards for the wire in the attic are only needed if the wire is within 6' of an access opening or within 7' where accessible by permanent stairs or ladder.

*

 

[theoldwizard1]

I still say, skip the electric heat. Install a propane heater. Get a 40lb tank and a 20lb spare. One person should be able to wrestle a full 40lb tank in and out of a car/truck.

Without electric heat a 60A panel should be more than enough.

Finally, how about running conduit on the outside of the house ?

 

[p912s]

Have you thought about using a Kerosene Heater instead of electric? I use one in my garage/shop and it heats the place quite well. It's one of the 23,000 BTU units that run on 1K.

I'd 2nd the idea of conduit on the outside of the house, if you went just above grade rather than up to the attic and back down you might save a fair amount of wire.

I too had the same concern recently of aluminum over copper. So I called on one of my clients that's a large commercial electrical contractor and was assured aluminum is ok; in fact it's what they use for all service entrance wiring. And the 2/3 with ground I bought was $150, in copper it would have been over $500.