Understanding a sub panel install....

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Old 09-06-08, 01:39 PM
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Understanding a sub panel install....

I'm looking into installing a sub panel in my house to do lack of breaker space in my main.

I have a 100amp Square D service panel with 16 spaces...which are full after a basement remodel and I have 6 more circuits plus the two off the main for the sub feed 50A breaker.

All the circuits going into the sub panel are for lighting and basically all the basement electrical outlets added during the remodel (4 breakers for the basement and 2 are for lighting/plugs from upstairs bedrooms and living room).

There will only be 15A breakers in the sub...the A/C, 20A breaker for garage etc are all located in the main....

The sub panel is going to be mounted within a couple of feet of the main and I do have a copper sewer drain to ground to but I'm lost on the neutral/ground from the main to the sub. I have a relative coming over to help who's got the electrical know how but I was kinda hoping to understand his expanation a little better. I don't want to be left in the dark and I hate not knowing what's going on.

To clarify...the feeder from the 50A breaker to the sub should be #8 wire correct (this is the only thing left I got to get)....and as far as wire goes, red and black go from the 50A to supply power to the sub panel, the neutral (white) connects to the neutral bar of the main box to the neutral bar of the sub panel and the grounds just ground from one box to the next? Do you still ground the sub panel to that copper pipe or is that not needed because the main is already grounded.

He said there was something more to it than just hooking the wires up...just wondering what he actually meant as I can picture it in my head.

All I know is I'm actually looking forward to it being done as it's the last big project down in the basement for this renovation. I just about finished installing a bathroom with a sewage ejector kit (which wasn't really all that fun having to bust up the floor to run the drains).
 
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Old 09-06-08, 02:28 PM
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Hello
I am not an electrician but I installed my own subpanel off of a 200amp GE main box. The most important thing to remember is that the ground and neutral HAVE to be seperate in the sub versus the main. In the main panel, the ground and neutral can be on the same buss. If the neutral and the ground are bonded together at the subpanel instead of being seperate, you will have parallel paths for current to return to the main panel; this is called objectionable current. The ground in the sub is NOT supposed to carry any current at all. The only time that is has current, as far as I know, is if a fault condition exists. I hope that my explanation helps. The pros will be along soon enough to correct me if I am wrong.
 
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Old 09-06-08, 03:34 PM
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You mentioned grounding to a copper drain. drain or waste lines are not good grounds although it is good practice to ground them. Not sure what your water system is there. If it is a well then it is likely the house plumbing, even if copper, is not grounded. It this case you would need to drive a ground rod near the panels outside and connect with #4 copper.

If you have city water and copper pipe coming in and throughout the house then a water pipe is probably a good ground. They usually put a jumper around the water meter if that is inside.
 
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Old 09-06-08, 08:51 PM
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All you need for your new subpanel is a 4-wire feeder from your main panel. (hot/hot/neutral/ground). In the subpanel, the neutral and ground need to be separated on separate busses, the neutral isolated from the box. In the main panel, the neutral and ground are connected to the same neutral/ground bus bar. The sub panel does NOT have any grounding/bonding other than to the main panel.

The wire between the two panels can be either a cable assembly, or PVC conduit with THHN wire between it. (You can use EMT or rigid conduit, but then you have to ground it, and besides, PVC is easier.

Note that the main panel should have a connection to the main water line (if metal), and should have ground rod(s), but again, that's in the main panel.
 
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Old 09-06-08, 08:51 PM
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After reading your comment dsc3507 I realized that originally when I bought the house the ground was on the 2" copper drain line....when I remodelled the basement I ended up running a water line close by to a couple of inches over so I could ground the electrical box to it...

You had me there after you commented on it that I had to go home and check cuz I was going 'don't tell me that I drywalled everything in and forgot to do that'.
 
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Old 09-06-08, 09:01 PM
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Originally Posted by Zorfdt View Post
All you need for your new subpanel is a 4-wire feeder from your main panel. (hot/hot/neutral/ground). In the subpanel, the neutral and ground need to be separated on separate busses, the neutral isolated from the box. In the main panel, the neutral and ground are connected to the same neutral/ground bus bar. The sub panel does NOT have any grounding/bonding other than to the main panel.

The wire between the two panels can be either a cable assembly, or PVC conduit with THHN wire between it. (You can use EMT or rigid conduit, but then you have to ground it, and besides, PVC is easier.

Note that the main panel should have a connection to the main water line (if metal), and should have ground rod(s), but again, that's in the main panel.

So I peaked inside the sub panel to be installed...what you're saying is that my relative is hooking the neutral to the neutral bus of the breakers (basically middle of panel where breakers are mounted), and from what I can see, the ground bar is located off i the interior corner of the box. I think I see where you guys are going. I'm still going to let him do it but atleast I'm getting the big picture now.

As far as everything else I've explained (as far as only putting lighting/light loads in the sub panel) that's a good plan correct? .... and I need that #8 wire to feed from the 50A right?

I was gonna look into a whole new Square D panel (with 24 spaces) but price wise for now putting a sub panel for those 6 circuits is like 1/3 of the cost of a new panel etc.

Anyways, this house has had a few hiccups (like the ground to the 2" drain) but I'm getting through them. My grandfather was a contractor before he retired and I used to do some work for him as a teen so I'm actually surprised I remember a thing or two.

I might actually cave in and get a grounding rod and drill a hole through my patio against the house to make it even better. My ground wire/elect panel is actually about 20' of water pipe away before it reaches the line coming out of the floor into the house.
 
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Old 09-06-08, 09:29 PM
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When you buy a panel it is usually jumpered to have the neutral bus grounded to the case. You need to break that jumper. when the neutral is bonded to the case - jumper installed - you connect the neutrals and ground wires to the same bus.

When you set it up as a sub panel you may need to buy an accessory ground block to install in the panel if there is not a separate one there already. The ground block would be bolted directly to the panel case. The neutral bus would be isolated from the case. Only (white) neutral wires would go to it and only ground wires to the ground bus.

As long as you have a good water pipe ground (not drain pipe) that goes coimpletely as copper to the street you should be OK but putting the rod in would certainly not hurt anything. I would try to avoid vrilling tha patio though. Maybe you could run it just a little longer to the edge.

For the connection I would use #6 even thought it is 50A protected. It is a short run and the difference in price is minimal. You may want to add something there and up that portection to 60A someday. Besides it never hurts to go larger.
 
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Old 09-06-08, 09:35 PM
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Originally Posted by dsc3507 View Post
When you buy a panel it is usually jumpered to have the neutral bus grounded to the case. You need to break that jumper. when the neutral is bonded to the case - jumper installed - you connect the neutrals and ground wires to the same bus.

When you set it up as a sub panel you may need to buy an accessory ground block to install in the panel if there is not a separate one there already. The ground block would be bolted directly to the panel case. The neutral bus would be isolated from the case. Only (white) neutral wires would go to it and only ground wires to the ground bus.

As long as you have a good water pipe ground (not drain pipe) that goes coimpletely as copper to the street you should be OK but putting the rod in would certainly not hurt anything. I would try to avoid vrilling tha patio though. Maybe you could run it just a little longer to the edge.

For the connection I would use #6 even thought it is 50A protected. It is a short run and the difference in price is minimal. You may want to add something there and up that portection to 60A someday. Besides it never hurts to go larger.
Well I can tell you there is a separate ground bar. It's off in it's own little corner in the panel. The neutral bus as I mentioned it part of the whole breaker setup piece but there are two screws on either end. One looks like brass, and the other white metal, with all the neutral hookups in between.

Maybe I'll go #6 for the hell of it. We're talking like 3' of wire. If I end up staying in this house and have to contemplate a 60A, I'll just upgrade the whole box. LOL. NOT! Where this panel is, there is no way to run more wire without busting the ceiling to get through the floor joists!

By that time, I can only hope I'll be in a new house...starting the projects all over again.
 
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Old 09-07-08, 01:37 AM
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You should use the 6ga instead of the 8. At 60C, which is what some circuit breakers are rated for, 8ga is only rated for 40 amps. Wire needs to be sized for whatever component in its path has the lowest temp rating. This is why old stoves ran 40A just fine on 10ga wire (10ga THHN is rated for 40A), or seemed to... everything looked okay until you pulled the cover off the back of the stove and the 60C rated terminals there were fried.
 
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Old 09-09-08, 11:51 AM
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I would recommend doing the following:

Go with 6/3 cable. It’s rated for the full 60 amps. You indicated the sub-panel will be next the main panel so a few feet of 6/3 will be cheap (<$10).

Go with at least a 16 space sub-panel. It will come with a main breaker to use as a disconnect. You “claim” to only need 6 spaces today, but think about the future. They are cheap, particularly since some come with a gang (10?) of 15 amp breakers. They also look more impressive that a silly little 6 slot box.

Move several 15 amp circuits have to the new sub-panel. This will not only free up the spaces needed for the sub-panel feed breaker (60 amps), but give me some extra spaces in the main panel for future expansion. Maybe you will install a bigger water heater or upgraded A/C in the future. Pick circuits to move that come into the main panel from the same side as the new sub-panel. They will be easy to move.

Lastly, have fun.
 
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Old 09-09-08, 12:49 PM
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Originally Posted by impeyr View Post
Go with at least a 16 space sub-panel. It will come with a main breaker to use as a disconnect.
Don't need a main in a sub panel if it's in the same building. Especially if it's sitting right next to your main panel. Buying anything other than a Main Lug panel is a waste of money for this application.


You “claim” to only need 6 spaces today, but think about the future.
He already is. Said he was moving...

They are cheap, particularly since some come with a gang (10?) of 15 amp breakers. They also look more impressive that a silly little 6 slot box.
Not as cheap as a ML and whether or not something looks impressive is hardly a reason to purchase. Prospective homeowners might appreciate seeing some extra slots. That's the only reason why the OP would want to go bigger than what he needs. Besides. Sounds as if he's already purchased one. Your a little late into the conversation. Hell, it's probably already done.
 
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