Electrical Sub-Panel.. ??

[SARGE..g-47]

Morning..

I had to add a sub-panel to be able to run a 2nd 220 v 30 A circuit. I came up short of space in the main panel box. By removing the existing 30 A 220v circuit breaker with intentions of moving it to the "sub" along with another 220v 20 A circuit, a space is left free for a 220v breaker in the main.

I intend to put a 60A 220 breaker in the main in that spot and run 6/3 wire to the sub panel. The question which is almost (almost is not for certain as I will be before connection) self explanatory is:

I do believe that 4 wires are required to go to the sub-panel. The two "hots" (black & red) go to the hot lugs. The ground wire to the ground lug and here's the question. I am assuming that the 4th wire must be bonded from the neutral bar in the main box to the neutral bar in the sub panel?

Even though I will be running 2 220v circuits from that sub box and a neutral wire is not required for them in that case, I assume the bond should be made from the neutral in the main panel to neutral in sub-panel with a neutral wire in case I want to add a 110v line that does require 1 hot.. a neutral and a ground connection from any panel period?

Am I correct or am I just assuming? Electrical guru's explanations are indeed Welcome!

Regards...

[Thom2]

here ya go Sarge .... http://www.bt3central.com/showthread.php?t=1

basically read everything in that thread that was posted by Don_Hart, he does an excellent job of explaining everything.

edit: sorry Sarge, I forgot how much of that thread is off your topic ... here's a link to the specific post that I was referencing .... http://www.bt3central.com/showpost.p...5&postcount=20

[Rich P]

IMHO, all things being equal run the 4th wire. It may not be required for 220 but would make it a more "normal" sub-panel. Also, if you ever want to pull an additional 110 off the sub-panel you would need it.

[SARGE..g-47]

Thanks for jumping in, Thom and Rich. I already purchased the 6 guage 3 wire (black.. red.. white.. separate copper ground wire) at my electricians suggestion with a 60 A circuit breaker and 2 1" connectors.

I have already have a 220 v 30 A I wired up and working in the main panel. This is the space I will vacate for the 60 A breaker to get 60 A to the sub-panel. I read what Don had to say about adding a 50 A to the sub and had never heard that before. I knew the white neutral my electricain had reccomended should be connected as I may run a separate 110 v line from that sub just for shop lighting.

After reading Don's explanation, I am still "not sure" what is referred to as a separate neutral bar not bonded to ground. My electrician had to go out of town on a job and I cannot ask or have him make the final connection as I had intended without waiting (which if I am not totally clear beyond a shadow of doubt.. I WILL WAIT).

I have already back-wired the new 220V 20 A to the sub-panek. I have already installed a juntion box to connect the existing 220 V 30 A in the main box to the sub panel about 18" beside the main to free the space for the 60 A. I have the 6/3, 60 A breaker and correct connectors. The only thing that remains is the actual connection.

Don's statement about putting a 50 A breaker in the sub panel and the neutral in that sub panel not connected to the ground and isolating it has put a "shadow of doubt" into what I do know of adding that sub panel. Perhaps I am dense with electricity... but dense and suspect is better than proceeding without knowing clearly what the correct destination and why is... ha.. ha...

Again... I may wait for my electricians return and let him make the actual hook up and throw the switch.

Regards...

[SARGE..g-47]

All...

Getting ready to leave for work... but I found the bond from the neutral bar to the ground bar Don H. referred to. There is a bar at the bottom of the 125 A sub panel (actually a standard panel used as sub) that crosses from the neutral bar to the ground bar. It has a large screw that attaches to both neutral and ground to bond them. The screw can easily be taken off and the bar removed. I do believe that is what he refers to in the sub panel by isolating the neutral from ground!

I understand the theory of dropping to one size smaller breaker in the sub panel. I had just never heard of it as I am not familar with running a sub. Will research more before I consider myself correct in my assumptions.

Thanks again...

[ssmith1627]

Certainly not advice that I want you to act on because I'm no electrician. But I have run wire and put a 100A sub panel in my garage to power my shop and the lights in my house along with the washer and dryer.

My understanding is that in the main panel, the neutral bar and the ground bar are bonded together.......that bar is in place to connect one to the other.
But in a sub-panel, those two are not bonded together. You have a separate neutral bar and ground bar. The white from the main goes to that neutral bar. The ground from the main goes to the ground bar......or I would think you could also ground that sub-panel to the earth directly.

Just more information for you to confirm. Just like anything else, if you don't feel comfortable in your facts, get some help -- too much at stake !

Steve

[SARGE..g-47]

Morning Steve..

I like you, am not an electrical guru. My working knowledge is excellent as I have run all my 220 V and 110 V myself and understand why what goes where. But... I have never seen or put a main panel or sub panel in place and I do have some doubt.

Yes.. the main panels neutral and ground are bonded together. Don H in his explanation from the former discussion on this forum mentioned not bonding in the sub panel. I also once heard that at FWW (Knots) where I have been posting for a number of years.. So!

I have installed the sub already about 18" away from the main box as my electrician told me it was out of code to go above or below the level of the main box. I used a standard 125 V box even though I am only going to take 60A to it with a 60 A breaker from the main to it as that is all I need, at the moment anyway. I have the correct 6/3 and double breaker to run the short distance.

The sub box (which is a standard 125 A box) I am using does have a bond bar running across the bottom that does bond the neutral bar to the ground bar. It bridges the neutral and ground bars. It is held by a large screw on each side and can be removed to break the bond in that second box.

I suspect that I only have to take that bond bar off and I simply have arrived at where I need to be. But... until someone with the proper knowledge tells me YES.. you are indeed correct, I will wait on my electrician to have a look.

And I agree with you about what you said. I just don't understand fully why that is done even though I suspect that since the bond is made from neutral to ground in the main box, a duplication in the sub box might possibly loop it to counter the action of why it is done in the main box??

Thanks for your in-sight as I believe we are correct in our assumptions. I just want to know for absolute sure why that is necessary before I "pull the trigger" and put a live round down-range. Perhaps my Ranger instinct leads me to be sure of the circumstances of where you step before you actually take that step! ha.. ha...

Thanks for your reply as it bolstersmy understanding of what I think is correct!

Regards...

[LarryG]

I just don't understand fully why that is done even though I suspect that since the bond is made from neutral to ground in the main box, a duplication in the sub box might possibly loop it to counter the action of why it is done in the main box??

That's basically correct. If you have four conductors from the main panel to the subpanel, and bond the neutral to ground in the subpanel, then the ground conductor back to the main panel will duplicate the neutral. IOW, it will be HOT. Not what you want, obviously.

[ssmith1627]

Here's the perfect explanation of why you don't bond the two together at a sub panel:

http://members.tripod.com/~masterslic/FAQ-2/18.html

"Why isolate the neutral in a sub panel?...
The neutral is only bonded to ground at your service panel. At all other points throughout your house, there is no connection between the bare (or green) grounding conductor and the white neutral conductor. Under normal conditions, the grounding conductor carries no current. No current means there is no voltage drop along it, therefore anything "grounded" to this conductor is at the same potential (voltage) as ground. If you bond the neutral and ground at the sub panel, than stray currents from the neutral return could go thru the equipment ground on the electrical devices fed from this sub panel. If you isolate the neutral and ground at the sub panel, than any currents would go back to the main panel, and go to the service ground. The main panel is where the neutral and equipment ground should be bonded.
If you install a sub panel outside the building from the main panel, than you will need to drive a ground rod at this panel. A single branch circuit run to another building is not considered a sub panel."

I hope that helps.

Steve

[SARGE..g-47]

Afternoon Larry and Steve..

And now it makes it all makes sense as to why. I think we are on a roll!

Gotta get to work and may proceed this week-end without aid of my electrician. I just remove that bottom bar to un-bond that second panel and isolate the neutral.

Thanks for the assist everyone that assisted. Ya know who ya are! ha.. ha...

Regards...

[SARGE..g-47]

Good morning guys and gals...

Here is a pic of the sub-panel... As I see it, the two hots are obvious and go to the two center lugs. The ground goes to the ground bar on right with the copper lug on top. The neutral is the bar on left.

There is a metal strap (I attached a piece of red duct tape to it) that bridges across on the bottom "bonding" the ground and neutral. It has a large screw on each side that attaches to the individual bars bonding them. That is the only place that bonds them as both bars sit on a plastic or nylon backing which does not allow them to ground to the metal box itself.

By removing the strap I have isolated the ground wire that attaches to the left ground bar from the neutral bar on the right?

Does anyone see it any other way? If so.. speak now or hold your peace before I burn my house down!

Regards...

[ssmith1627]

Once that bar is removed you should be in good shape. There's probably a green screw that will bond the ground bus to the box itself. But the neutral bar would be free of connections to anything except the neutral wire from the main panel.

Here's how mine looked when I had it about 3/4's full:

http://ssmith1627.myphotoalbum.com/v...d=142_4254_IMG

Mine was set up as a 100A sub panel so I had to run 2/3 wire from the other end of my house.....probably 90 feet......where the main service panel is located in my crawlspace. The garage of course is on a slab so I had to go up into the attic, across the house, and down into the panel in the garage. With that huge freakin cable it was quite a challenge. That stuff had been coiled and was not easy to work with -- it really looks like the size of the wires that come to the house from the road ! haha (not quite though since those carry 200A service)

Steve

[LarryG]

Um, yes, I do see it another way.

Those are both neutral buses. I count twelve breaker spaces in this panel. You can connect up to two wires per breaker, or 24 total, ergo there's a bus with 12 screws on the left for the left side breakers and another bus with 12 screws for the right side breakers.

The lug at the top of the right-hand bus is for the connection of the neutral wire coming from the main panel. Since this connection is made at only the right side, the bar you've marked with red tape bridges the two neutral buses electrically.

With some panels the ground bar must be bought separately, at extra cost; that may be the case with yours. The ground bar typically screws directly to the panel housing so that it, the housing, will be connected to ground. (That's why both of these neutral buses are isolated from the housing ... so that don't have to bond the neutral to ground unless you need to. Which, as we've already established, you don't.)

[jessrice]

Larry is right,

a lot of panels sell the grounding bars separate. The last few 200 amp panels i have bought all required the separate purchase of the grounding bar. They are a few dollars each, and vary in the number of connections.

The panel box needs to be grounded, so that if a wire does come loose and touches the box, the box isnt live when you go to open it. Also once grounded, any metal conduits that you have coming from the box will also be grounded, and not be live should a hot wire touch them.


Also each neutral requires it own spot, so if you would double up wires to the breakers, you would be short neutrals

Jesse

[SARGE..g-47]

Thanks again guys.. After reading your post after I got home from work, I went down and looked at the GE card-board box the new panel came in. In fine print on it was stated... "Ground bar not included". That about says it all!

At this point, I will wait till my electrician comes back into town and just let him do it while I observe. That appears to be the safe approach for me anyway. ha.. ha...

Regards...