sub-panel ground/neutral question

[Bob S2]

Hopefully tonight I'll get the last freaking piece of conduit in, and I'll be able to run the wiring. I understand that in the main box the neutral and ground are basically the same, but in the sub-panel the ground(bare or green) and neutral(white) need to be separated. This is to keep from having current flowing through pipes, etc. in case of wiring failure of the neutral, I believe. I understand how you don't want that to happen, makes sense.

What I'm not understanding is how they refer to the bars in the sub-panel being separated. Wouldn't that mean that on one side of the panel the breakers would have the white connected to the white and the other side of the panel would have the breakers connected to the ground?
Ah wait, I think I kinda just had a flash of some understanding. In a main panel, you tend to wire the white(neutral) next to the breaker it corresponds to. In a sub-panel, do you run the neutrals all over to the neutral bar? If so, does this mean that unless you run a green/bare wire on a circuit the ground bar will not have connectors other than back to the main box? That must mean that the ground bar, which was previously a neutral bar, was NOT in contact with the box itself, and probably would want to be now that it's a ground bar.
Just looked further, and the ground in the main box connects to the white/neutral bar, so the statement in the last sentence is wrong.
Can anyone help me follow this? I'm gonna have an electrical guy inspect what I do, I just want to understand the reasoning behind it 100 percent if I can.
Thanks!
--bob

[Sberry]

There will be a bonding screw (green) or a strap that comes with the panel. You do NOT use it on a sub. There will be listed an auxilary ground bar kit that fits the new panel, you have to buy it seperate and it screws to the can, or box itself. The neutral bar is already installed, hook all the white wires to it, doesnt matter where they go. Any green or bare wires go to this aux ground bar. You should bring the 4th wire from the panel from an equipment ground bar or I would rather put it to the neutral bar to this aux ground bar in the sub. If you use EMT, metal conduit all the way between the 2 panels you do not need the 4th wire if you do not want to use it, the conduit may act as this wire. There will also be the neutral wire coming from the main, white, which connects to the neutral in the sub. Even though the N and G terminate in the same place in the main they do seperate functions in the sub. The N is a part of the active circuit when using 120V and we want these currents running back to the main on an insulated wire and not on the chassis grounds. The only time there would be any current on the equipment ground wire would be in the event of a short circuit. If they are bonded at the sub (incorrect) the neutral currents may take either wire.

[Planet X]

See the attachment. The bar connecting the left and right buss bars (lots of shiny screws) will be removed so the neutral and ground wires are electrically seperated in the sub. They come back together at the main breaker panel (the one that gets power from the pole).

All circuits in the sub will be wired like normal. Green/bare copper to the ground buss bar. White neutral wires will go to the neutral buss bar.
The power wires 120 or 240 will go into the appropriate circuit breaker.

Wiring A house by Rex Cauldwell- tauton books. is should be on your 'diy' reference library book shelf. Or something similiar

[Bob S2]

Thanks guys, that makes a lot of sense. That picture looks exactly like the box I have, so it helps a lot. I see the separate ground block, I'll pick that up when I buy the wire, hopefully tonight.
So, just re-phrasing, neutrals carry return current normally, and in the event of a fault condition, the ground would pick that up and carry it to the main panel. If they were both tied together at the sub-panel, the normal return current can go through the ground instead of the neutral at any point.
I think I got confused because I was looking at the web site, and they show how you should disconnect the ground and neutral blocks. I think it might be technically correct but may lead one to think that one side is the ground and the other side is the neutral.
The web site is: http://www.taunton.com/finehomebuild...ges/h00009.asp
What do you guys think of the diagram labeled "improperly wired subpanel"?

--Bob

[Sberry]

As shown in that panel some boxes allow for the seperation of the neutral bars making one a ground bar, when this is done the bonding screw MUST then be installed in the one that is to become the ground bar bonding the box to that bar.

[Bob S2]

Thanks Sberry! Unfortunately, no wiring going on tonight. Not only is it too cold out there but this afternoon I was in a fender bender in the Sports Authority parking lot. Was backing out, saw a car zipping across lanes. it came out from between 2 other cars and turned into my bumper as I was backing out. According to my insurance agent my backing out puts me probably at fault even though I'd stopped. Argh! Her whole passenger and rear door is really messed up. My rear bumper is tweaked a little, and a little baseball size dimple right behind the bumper corner pushed in. Funny thing is, I might not even get it fixed, since it's not that bad, or I might just buy a new bumper myself. Get this though, the state farm autobody shop quoted the damage to my truck as 1,200 bucks! Most of it was in painting the side, clearcoating the side, blah blah blah. It's a 93 ranger, with way over 100K on it. Bad thing is, my insurance will go up. This is the first time in like 15 years I've had anything happen other than parking tickets and 1 speeding ticket. Argh.
--Bob

[Sberry]

Thank Planet X too

[Bob S2]

Yes, Thanks PlanetX! I don't think I'm going to try pulling wire for the next few days, it's going down into the single digits and not coming back until next week. Xmas is going to be brutal, with windchill way below zero it sounds like. And the worst is that Indiana is once again getting all the good stuff. Chicago isn't getting anything other than flurries. Argh!

[Planet X]

Yes, Thanks PlanetX! I don't think I'm going to try pulling wire for the next few days, it's going down into the single digits and not coming back until next week. Xmas is going to be brutal, with windchill way below zero it sounds like. And the worst is that Indiana is once again getting all the good stuff. Chicago isn't getting anything other than flurries. Argh!

Two words.................Klein Tools