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Old 02-18-2005, 11:33 AM
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Electrical sub panel help

I hope someone here could give me a little more guidance. I've searched and read the threads but I'm still a little confused. What I want to do is run a 100 amp? sub panel to my garage from the main panel in the house. I talked with an electrician and he said if I basicly did all the bs grunt work he would hook everything up and check over it pretty cheaply. He said run 3 #6 four wire underground from main panel to new sub panel and a #10 ground wire. I am confused as to what wire I am suppose to get and run actually. He said its a 4 wire in 1 then you just split it when you get to the panel. Then I want to run a few more outlets and at least 1 220 volt outlet. How difficult is it to add once the main sub panel is in? I am gonna go to the electrical supply house and talk to them, but any knowledge I could gain before going there would be great. Sorry for the long post. Thanks for any help.
~Anthony
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Old 02-18-2005, 04:48 PM
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what tools do you plan on running in the garage? that will determine how much power you need. the #6 wire your electrician buddy mentioned is good for 60 amps, which is plenty, but again, how much do you need.

how far away is your garage? you may want to put a 100A service out there, but when you see the price of the #3 awg wire you might change your mind and go with something lighter.

if you have a fairly long run and want to save a few $$ you could run aluminum wire underground, which is around 60% of what copper wire costs.

you will want to run a 4-wire cable, that is 2 hots, 1 neutral and 1 ground. then you will have 220v power out there if you want it. (2 hots).

basically you have to be realistic about what you want in your garage and how much you want to spend doing it.

JB
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Old 02-18-2005, 06:24 PM
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It sounds as though your garage is detached. If so, here's what I'd do. Go to Home Depot, Lowes, ect and get #1 aluminum "USE" this stands for Underground Service Enterence. It's dirt cheap, pardon the pun. It is direct burial cable that needs to go 18", use PVC to transition from th ground to the box. If the garage is seperate, the panel get treated exactly like your house except no meter, meaning that your house has 3 wires coming from the pole. In the panel, the neutral bus will get grounded to the shell of the pane via a green screw supplied. If the garage is atached to your house, then you need 4 wire "USE" cable. The ground & nuetral are seperate from one another. Also I forgot to mention if the garage is seperate, you'll need to drive in at least 1 ground rod, maybe 2 depending upon the inspector. IIRC, you must have no more the 3 ohms impeadence to ground but it's hard to prove and a lot cheaper to buy another $10 ground rod, no more then 6 foot apart.

IMO, don't waste your time on anything less then 100 amp panel. They're so cheap plus with the larger gauge wire, you'll cut down on voltage drop. Be sure to use an anti oxident compound on the aluminum wire. Don't worry about using aluminum, I've never seen a failure from using it in residential applications. Just to let you know that the drop from the pole to your house that the utility installs is aluminum!

You're doing all the grunt work! Make friends with the inspector, he's not the enimy, he's looking out for your safety. Ask him for any special local requirements. Yes, I'm an electrician.
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Old 02-19-2005, 10:33 AM
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Thanks for the help so far everyone, the garage is attached but its a split level home so I thought it is probably easier to go around the side and into the garage than routing the new wire. The electrician is a friend of a friend sort of deal and the guys seems pretty strange so Im not sure if Ill use him. And I just noticed the house only has a 100 amp panel right now is it possible from me to run a 100 amp sub panel to the garage. bigger is always better right
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Old 02-19-2005, 11:48 AM
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I just went and took another look at my panel and it looks like I have 2 unused 50 amp breakers installed. Can I just run off these to another panel in the garage? Sorry I think Im confusing myself more than ever.
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Old 02-21-2005, 09:03 AM
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I ran A 50 AMP breaker in main box, then use 4 wire to subpanel. I just used a cheap one with 6 position and no main in it. I ran two 220 outlets for compressor and welder, plus 2 more circuits for plugs on either side of the wall. I figure I have around 300-350 in parts at least. My sub panel by the way is only about 10 feet from the main panel. I think you will find it very difficult to get #1 wire in your small Main panel. When they added a 60amp for my a/c it was cramped. I personally think a 100amp would be way more than what you need. You may actually be better off upsizing your main panel in the long run. More expensive but then you would be set for many years
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Old 02-21-2005, 10:14 AM
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Hi guys,

I read the posts and have a question. I just had my house upgraded to a 200 amp service a Cuttler Hammer CH was installed. I did this to have the electrician run a 100 amp service to my garage. The correct cable was used and everything went very smoothly. The distance from the main box to the sub is about 25 feet. I had one receptacle (15 amp breaker) only for my 30 gal, 5 horse craftsman compressor installed. When I turn it on the breaker trips after a few seconds. I upped it to a 20 amp breaker and still the same thing. The compressor works on the old receptacle just fine with certain lights off which was always the way. I left a message for the electrician but he is away for two weeks. I am so frustrated. There were no problems with the install and everything else is great. Could I be overlooking something? The sub panel is a square D and I didn't buy it, a friend gave it to me and he said it was almost new. Do they go bad? Any light you can shed would be appreciated. Thanks

Dave
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Old 02-21-2005, 11:45 AM
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I don't think your electrician knows what he is talking about. Wiring to feed a 100 amp panel must be sized to 125% of the rated capacity of the load, IE 100amp. 100 X 125%= 125amp. #6 wire is good for only 65 amps. For 125 amp protection you need to run minimun #1 AWG wire which is good for 130 amps. What you need is a 3 conductor #1 with ground (red, black, white). If you cannot get hold of a 3 conductor #1 you will have to run 3 seperate #1 wires, plus a ground conductor. In a 3 conductor #1 wire the red wire will attach to one hot buss of the sub panel, the black wire to the other hot buss of the panel. White wire to the neutral buss of the sub panel. The ground wire will run from the ground buss of the main panel to the ground buss of the sub panel.

Stay away from aluminum wiring, it is trouble waiting to happen. The only time a utility provider uses it is for service drops from the pole to your weather head. Then it is compression spliced to the copper wire from your distribution panel. Aluminum wire has problems when you try and secure it to a screw connection because the expansion and contraction is so radically different than copper. Over time a screw connection to aluminum will become loose due to expansion and contraction and increased resistance will result.

Vince

Last edited by 302/Z28; 02-21-2005 at 12:09 PM.
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Old 02-21-2005, 12:19 PM
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Here is what I did in my detached garage. I am a one man show, so having multiple machines running at the same time doesn't occur. First, I put a 50 amp 220 breaker in my main 200 amp panel. I ran #8 wire from my main to the detached garage through underground conduit (3" pvc pipe). The run is approximately 60'. I bought a 100amp main panel at home depot for $50. I put a 50 amp main breaker in the panel. I then wired my lights, outlets, 220 compressor, future garage door opener on separate circuits. Drove an 8' ground rod wired to the sub-panel. I just finished adding another 16' to this garage and wired two more circuits for lights and outlets in the new addition. This will be my woodshop. I may have dust collection and saw or planer going, but I really shouldn't ever have two high draw machines running at the same time. (ie: mig welder & compressor)
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Old 02-21-2005, 12:47 PM
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[QUOTE=Toyman]Here is what I did in my detached garage. QUOTE]

What you did was derate the 100 amp sub panel by installing a 50 amp main breaker in the sub panel, which is perfectly acceptable.

Vince
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Old 02-21-2005, 01:00 PM
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i can feel you pain. i am TRYING to install a 200 amp service to my garage- it only came with a single 20 amp connection- enough for a single light bulb and the garage door opener. What an undertaking! I just finished buying everything except the service entrance cable. I'll be happy to bounce ideas off you or collectively put our heads together so we can both get our shops up and running.

i have to dig a ditch from the garage to the power box on the street and it is a bit over 150 ft. the ditch must be at least 2 ft deep- since i am tapped out at the moment i am doing it all via shovel in some hard/Colorado/clayish stuff. A little here a little there and i might finish in my lifetime! since this is a completely seperate system from my house i also have to install the 'ground ' so that will be another 40 ft long trench at least- unless i can find some code saying i can put it alongside the service entrance in the same ditch. a side benefit to all this digging is my arms are getting bigger :lol:

i am also looking for a supplier for the 2-0/ 4 strand cable i need to hook into the power box. (not likely to be cheap!) Anyone live near Colorado Springs and have a good source? Home Depot and Lowes just don't carry anything like that.

i don't really care to play with electricity and have been relying on a lot of homework with electrical books to work out the supply list. Hooking it up is another issue- maybe i can muddle through it all with out getting electrocuted but i got pizza and beer for any knowledgable parties willing to pitch in. (sorry no lite beer at my place only the non-human filtered stuff)


assuming everything won't be run at once:
50 amps mig (Lincoln Power Mig 200)
50 amps plasma cutter (Lincoln Procut 55)
50 amps air compressor (TBD since last one just died)
40 amps lighting circuits
40 amps misc plugs
20 amps KEG-o-RATOR!
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Old 02-21-2005, 01:28 PM
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Quote:
Originally Posted by 302/Z28
I don't think your electrician knows what he is talking about. Wiring to feed a 100 amp panel must be sized to 125% of the rated capacity of the load, IE 100amp. 100 X 125%= 125amp. #6 wire is good for only 65 amps. For 125 amp protection you need to run minimun #1 AWG wire which is good for 130 amps. What you need is a 3 conductor #1 with ground (red, black, white). If you cannot get hold of a 3 conductor #1 you will have to run 3 seperate #1 wires, plus a ground conductor. In a 3 conductor #1 wire the red wire will attach to one hot buss of the sub panel, the black wire to the other hot buss of the panel. White wire to the neutral buss of the sub panel. The ground wire will run from the ground buss of the main panel to the ground buss of the sub panel.

Stay away from aluminum wiring, it is trouble waiting to happen. The only time a utility provider uses it is for service drops from the pole to your weather head. Then it is compression spliced to the copper wire from your distribution panel. Aluminum wire has problems when you try and secure it to a screw connection because the expansion and contraction is so radically different than copper. Over time a screw connection to aluminum will become loose due to expansion and contraction and increased resistance will result.

Vince

You're wire calculations are right generally speaking. For residential ONLY, there is a seperate table for service conductor sizes. A 100 amp rerquire #4 copper or #1 aluminum...even for a sub panel. While I'm not a fan of aluminum wire, I'll bet well over 95% homes have aluminum service enterence cable. It's a real oddity to see copper. I have never seen aluminum service enterence cable fail, not that it hasn't happened. Even when anti oxicedent compound hasn't been used. I can honestly say that I've seen more problems with copper wire failures with insulation. I credit this to old age since almost all insulation failures have been on very old wire.

There are a lot of factors technically to consider when sizing a panel for a house or for any other building. There's a lot of de-rating going on. I'll be willing to bet that short of electric heat or central air running, you could power a typical house on a 240 volt, 30 amp breaker and it wouldn't trip! I did a service change on a co-workers house that was about 1,600 sq ft. The house had a 30 amp 120 volt service. I pwered the whole house on that with my portable generator. The home oowner was home with all the lights, Xmas lights on and TV going! Not a single problem on a 30 amp 120 volt breaker.

100 amp stuff is just so cheap plus the larger size wire cuts down on voltage drop, it's just not worth farting around going to a smaller size wire or panel. It's like comparing a 200 amp service to a 150 amp service. It's just not worth while doing the 150 amp, costs are almost exactly the same, maybe cheaper for the 200 amp in some cases.

To all, my reponse to Vince is not meant to repond so much to him but rather that he brought up a lot of good points on this topic.
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Old 02-21-2005, 01:34 PM
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Quote:
Originally Posted by adivito
I just went and took another look at my panel and it looks like I have 2 unused 50 amp breakers installed. Can I just run off these to another panel in the garage? Sorry I think Im confusing myself more than ever.

Since you already have the 50 amp, 2 pole breaker, just use that. Why buy more parts then needed. Keep the 100 amp wire and panel. Down the road if you up grade the house service you can plug in a 100 amp breaker.

Actually, you could use a 100 amp breaker even though your house is 100 amp service. You could even get away without a breaker since the wire would be sized for the main breaker and the main breaker would be actually protecting the sub panel wiring. I wouldn't recomend this since any servicing of the sub would require you to shut the power off to the house...not really convienient.

Keep the 100 amp panel & wire, use the 50 amp breaker, you won't see any drop in performance and I doubt you'd ever trip the 50 amp breaker.
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Old 02-21-2005, 01:37 PM
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Quote:
Originally Posted by daveh
Hi guys,

I read the posts and have a question. I just had my house upgraded to a 200 amp service a Cuttler Hammer CH was installed. I did this to have the electrician run a 100 amp service to my garage. The correct cable was used and everything went very smoothly. The distance from the main box to the sub is about 25 feet. I had one receptacle (15 amp breaker) only for my 30 gal, 5 horse craftsman compressor installed. When I turn it on the breaker trips after a few seconds. I upped it to a 20 amp breaker and still the same thing. The compressor works on the old receptacle just fine with certain lights off which was always the way. I left a message for the electrician but he is away for two weeks. I am so frustrated. There were no problems with the install and everything else is great. Could I be overlooking something? The sub panel is a square D and I didn't buy it, a friend gave it to me and he said it was almost new. Do they go bad? Any light you can shed would be appreciated. Thanks

Dave

The problem is that the 15 amp circuit you're using for the compressor is 14 gauge and just to small. It has a lot of resistance and the compressor can't get up to speed quickly enough. You need 12 gauge wire!

Putting a 20 amp breaker on 14 gauge, 15 amp wire is a bad practice!
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Old 02-21-2005, 02:16 PM
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Quote:
Originally Posted by Huskinhano
You're wire calculations are right generally speaking. For residential ONLY, there is a seperate table for service conductor sizes. A 100 amp rerquire #4 copper or #1 aluminum...even for a sub panel. While I'm not a fan of aluminum wire, I'll bet well over 95% homes have aluminum service enterence cable. It's a real oddity to see copper.
All service entrance conductors are aluminum, but with specialized connectors that eliminate any chance of the connection loosening over time. Those connectors are designed to mate aluminum service drops (from utility supplier) to the copper conductors that come out of your weatherhead. The problem, as stated with aluminum wire is when it is used with screw connections.

Vince

Last edited by 302/Z28; 02-21-2005 at 03:17 PM.
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