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bigbassg 05-30-2007 12:34 PM

Wiring a subpanel
 
Hey all,
I have a quick question. I am finishing off my basement and am planning on running a 100 amp subpanel to my basement from the main box. I have a 200 amp main box. What size wire do I need to use. I have heard 2 guage is for 100 amps? Will that 4/0 4/0 2/0? As far as I understand it should be 4 wires with hot hot neutral and ground and both the neutral and ground will be run to the ground bus in the main box. Also most of the large power consumers currently are on one leg of the main box. I am planning on pulling this off the other leg. Will this help to make the power cleaner on the subpanel?
Thanks,
Mike

JohnJ0906 05-30-2007 04:08 PM

#2 copper is OK. You can also use #3 copper, if you can find it.
#1 AL if you use Aluminum.
Ground con be smaller-#8 cu or #6 al.
Neutrals and grounds completely separate at sub-panel
You will be using BOTH legs at the main panel- a double pole breaker is arranged that way.
Are you using conduit or cable?

keyser soze 05-30-2007 06:36 PM

Sorry to hijack a little but this is related. I might be confused about what you said but my main panel has two bus bars for grounds and neutrals. My initial electrician did not seperate them out. Each bar has both grounds and neutrals on it. Is this acceptable? I asked a few people and they said it was fine but none of them were licensed from what I remember.

Do you say "neutrals and grounds completely separate at the sub panel" becasue they should only be terminated togther at the main panel? I asked a buddy once if there was any real difference between ground and neutral since they are the same at the panel. He said there is a difference in that they should not cross paths out in the house, only at the panel. Was he basically correct? He was putting it in "laymans terms" for me obviously.

bigbassg 05-30-2007 09:07 PM

Okay I see about using both legs that's fine. I've checked into it a little more and I've 2 2 2 4 which I think should serve the purpose well. I will be using wire not conduit. Is this okay? As far as the grounds and neutrals on the main panel. I believe they both can come off the same bus bar at the main, but they will be separated in the sub panel. Also doesn't the white wire act as ground on a 220 circuit? You have two hot wires in 220 and one ground in which the white becomes ground as far as I understand.

NateHanson 05-31-2007 08:09 AM

No, in a 220V circuit you have two hot wires, a ground (green or bare) and sometimes a neutral as well. But the neutral is only necessary when the 220V appliance has 120V loads as well (like an electric dryer with 120V controls).

For a straight 220V appliance, like a tablesaw, you can use 12-2 romex (or whatever the appropriate gauge), and in that case the bare wire is the ground, the black and white are hots (put black tape around the white wire at each junction to reassign it as hot), and there is no neutral in this circuit, because the 220 V difference is between the two hot wires themselves. In a 120V circuit the voltage difference is between one hot and ground, and that connection to ground is provided by the grounded conductor (aka the neutral wire).

JohnJ0906 06-01-2007 04:02 PM

Quote:

Originally Posted by keyser soze (Post 47036)
Sorry to hijack a little but this is related. I might be confused about what you said but my main panel has two bus bars for grounds and neutrals. My initial electrician did not seperate them out. Each bar has both grounds and neutrals on it. Is this acceptable? I asked a few people and they said it was fine but none of them were licensed from what I remember.

Do you say "neutrals and grounds completely separate at the sub panel" because they should only be terminated together at the main panel? I asked a buddy once if there was any real difference between ground and neutral since they are the same at the panel. He said there is a difference in that they should not cross paths out in the house, only at the panel. Was he basically correct? He was putting it in "laymans terms" for me obviously.

At the Main Service Entrance Only, the grounds and nuetrals can be together. Usually in a house it's the panel with the main breaker. ALL other places, the grounds and neutrals must be seperate. If you have a seperate disconnect between the meter and panel, the disconnect would be the ONLY place where grounds and whites got together.

Grounds and nuetrals together is the EXCEPTION! to the rule.

J. V. 06-02-2007 11:20 AM

A 100 amp panel requires # 3 copper for the two hots and the neutral. (You can derate the neutral, but why bother yourself).
One # 8 for the ground. Total 4 wires. The ground (ECG) wire must be green. The neutral must be marked with white phase tape at each termination.
The green # 8 ground will terminate at the ground terminal strip. If the panel has no grd terminal strip, you need to get one and install it.
The # 3 neutral will terminate in the lug provided.
Separate grounds on one terminal strip and neutrals on the neutral strip.

I would suggest you run EMT or less preferable PVC conduit from the main panel to the sub-panel. It is impossible to find wires of this size and quantity in cables.

You will need a 1" conduit if you use THHN, THWN wire ect....what they sell at the big box stores like Home Depot and Lowes.
Do not use more than 4 90 degree bends in one run of conduit. If you must have more than 4 (360 degrees) you will have to set an accessible box somewhere in the run.
And yes, John is right on about the bus bars. You could put every breaker on one side of the panel and it would be balanced.

ps....The only reason you can connect ground's and neutral's at the main service is because you only have three wires present. You can actually make a sub-panel a main panel with three wires. But that is another discussion.

bigbassg 06-02-2007 04:09 PM

Okay. I think I understand everything to some extent. Anyway I ended up using 2 2 2 4 direct burial cable. The box I used it a main lug and the ground and neutral buses are separate in the box so I put them each on their own bus there. I also took a closer look at the box and I see what you're talking about with the legs being balanced. Thanks a lot for the help and I'll let you know if I have more questions.
Mike

brantmacga 06-02-2007 04:27 PM

Quote:

ps....The only reason you can connect ground's and neutral's at the main service is because you only have three wires present. You can actually make a sub-panel a main panel with three wires. But that is another discussion.
have you ever done electrical work?

Speedy Petey 06-02-2007 06:21 PM

Quote:

The only reason you can connect ground's and neutral's at the main service is because you only have three wires present.
Well this is absolutely not the reason, but you can feed a sub-panel with three wires under some circumstances.

J. V. 06-03-2007 10:57 AM

What I meant to say is that you can you can make a sub-panel a main service panel. Two ground rods, bonded neutral. Basically instal as POCO would. No ECG required. Three wire service entance. POCO doesen't give you a four wire service. It's a three wire service and can be copied for the sub-panel.

Brantmacga. Yes, I have done electrical work before. I am a licensed Master Electrician and Licensed electrical contractor.

Speedy Petey....Exactly what I meant.

JohnJ0906 06-04-2007 04:34 AM

Quote:

Originally Posted by J. V. (Post 47525)
What I meant to say is that you can you can make a sub-panel a main service panel. Two ground rods, bonded neutral. Basically instal as POCO would. No ECG required. Three wire service entance. POCO doesen't give you a four wire service. It's a three wire service and can be copied for the sub-panel.

Do you mean changing the subpanel to the main service entrance?
If you mean at an out-building, yes, but only if you have NO other metallic paths back to the main- no metal water or gas piping, no CATV, phone, intercom, etc. AND the 2008 NEC will remove this.

terrynistler 06-28-2007 02:57 PM

JV not picking on you but where are you licensed at?

J. V. 07-01-2007 01:23 PM

terrynistler,
South Carolina.
Contractor license # M 98019
Masters license # 022121197
No offense taken.......John :)

Dan101 07-01-2007 01:53 PM

Mike,
Double check your local codes just to make sure everything you are using is approved for your area. Just because they sell it at Home Depot or Lowes, doesn't always mean it is approved in your city!


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