Panels, Grounding Bars and Bonding Screws

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Old 08-22-06, 06:57 PM
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Question Panels, Grounding Bars and Bonding Screws

A year or so ago, I had an electrician install a new 200A 40 space Siemens service panel in my house. I had the electrician leave the original 100A panel in place so that I'd still have electricity while I got round to gradually replacing all the branch circuits in the house, and connecting them to the new panel. I've finally got round to starting this job, and as I do, I'm wondering if the new panel was installed correctly...

My setup is like this:

- The power company's wires arrive as an overhead connection (three wires) and enter into a weatherproof combo meter / circuit breaker panel attached to the outside of the house.

- This relatively small outside circuit breaker panel has a 200A main breaker (labeled "service disconnect") and hot "feed through" terminals that supply heavy wires that run through metal conduit, going around the house, and then entering the house about 30' away to connect to the new 200A panel inside.

- The main neutral is connected to a bus bar in the outside cabinet. This neutral bar is grounded via a connection to a single buried copper grounding rod near the outside panel.

- A heavy neutral cable and another grounding cable run from this neutral bus bar through the metal conduit mentioned above, to the new 200A panel, making 4 wires in total arriving there (two hot, a neutral and a ground).

- Also in the outside cabinet is a 100A 2 pole breaker that supplies the old 100A panel - this will will eventually be eliminated once I've installed all the new branch circuits.

- Over to the new 200A panel inside the house. The two incoming hot wires are connected to the two legs of the panel. The incoming neutral is connected to the right hand neutral bar. The grounding cable is attached to a small grounding bar in the corner of the cabinet (that is attached electrically to the cabinet), and also to the grounding bushing of the metal conduit carrying the supply wires.

- A further grounding cable connects this small grounding bar through a wire to a clamp on my copper water supply piping.

- The main grounding bar on the left side of the panel is tied with a connecting wire to the neutral bar on the right. Neither bar is bonded to the case, and hence to the ground connection. The green bonding screw is missing.


So, my questions are:

A) If the neutral is connected to ground at the outside panel, shouldn't the neutral and grounding bars at the inside panel be disconnected from each other? This is my understanding if the 200A panel is treated as a sub-panel, but maybe it's treated as a main panel since it's supplied by feed through terminals from the outside panel?

B) And if the neutral and grounding bars in the inside panel ARE supposed to be disconnected, shouldn't the left hand grounding bar in the inside panel be bonded to the panel case with the bonding screw? It's currently insulated as far as I can tell.

C) On the other hand, if the inside panel is treated as a main panel, and so the neutral and grounding bars are supposed to be tied together, then shouldn't one of the bars be bonded to the case with a bonding screw?

D) Is it OK for there to be one ground at the external panel (the buried rod), and then the second ground at the interior panel (the water piping)? They are all connected together electrically, but I wasn't sure about distance factors.


Many thanks in advance if you've read this far and have anything to say about my situation!

Oh yes, I live in Santa Fe, New Mexico, USA.

Cheers,

Simon

P.S. While I'm here, why are there only about 37 terminal connections on each of the neutral and grounding bars? If I fill my 40 space panel with single pole breakers, doesn't that leave me three terminals short? Not a problem since I'll have several 2 pole breakers, but it has me slightly puzzled...
 
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Old 08-22-06, 07:16 PM
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A) If the neutral is connected to ground at the outside panel, shouldn't the neutral and grounding bars at the inside panel be disconnected from each other? This is my understanding if the 200A panel is treated as a sub-panel, but maybe it's treated as a main panel since it's supplied by feed through terminals from the outside panel?

This is improper. You cannot have the inside panel fed by feed through power. It has to be able to be disconnected at the main panel. Along with this, the neut and grounds should be seperated in the sub panel

B) And if the neutral and grounding bars in the inside panel ARE supposed to be disconnected, shouldn't the left hand grounding bar in the inside panel be bonded to the panel case with the bonding screw? It's currently insulated as far as I can tell.

Usually the ground bar mounts directly to the tub. If it doesn't, then yes, it needs to be bonded to the tub. The neut must be isolated at this point.

C) On the other hand, if the inside panel is treated as a main panel, and so the neutral and grounding bars are supposed to be tied together, then shouldn't one of the bars be bonded to the case with a bonding screw?

It cannot be a main panel. All power must be able to be disconnected from the one main panel outside. The inside panel must be connected and bonded as a sub panel should be

D) Is it OK for there to be one ground at the external panel (the buried rod), and then the second ground at the interior panel (the water piping)? They are all connected together electrically, but I wasn't sure about distance factors.

The pipe needs to be connected at the service equipment.

A question on the outside panel:

Are you sure the line side power is not backfed through the 200 amp breaker. If the inside panel is then fed from the bus as feed through, this would then make that acceptable but the inside panel still needs to be treated as a sub






P.S. While I'm here, why are there only about 37 terminal connections on each of the neutral and grounding bars? If I fill my 40 space panel with single pole breakers, doesn't that leave me three terminals short? Not a problem since I'll have several 2 pole breakers, but it has me slightly puzzled

Let me know when you figure that one out as well. I would guess the designers figure you will have at least a couple 2 pole breakers. Other than that, who knows. They are always doing things that don't make sense to me.

btw- you can double on the grounds but not the neuts
 
  #3  
Old 08-22-06, 08:21 PM
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Originally Posted by syperk
A) If the neutral is connected to ground at the outside panel, shouldn't the neutral and grounding bars at the inside panel be disconnected from each other? This is my understanding if the 200A panel is treated as a sub-panel, but maybe it's treated as a main panel since it's supplied by feed through terminals from the outside panel?
Originally Posted by nap
This is improper. You cannot have the inside panel fed by feed through power. It has to be able to be disconnected at the main panel. Along with this, the neut and grounds should be seperated in the sub panel
Hmmm, but this combo outside meter/panel seems to be specifically designed to supply a second panel via the feed through terminals. The hot wires from the meter half of the unit attach directly to a 200A main breaker which seems to control the feed through terminals, so flipping this breaker will shut off power to the inside panel.

Basically, this external box just contains the service disconnect, while the inside panel contains all the branch circuit breakers (and an additional 200A main breaker). So I think there's nothing fundamentally wrong with the setup, except that I'm not sure if the inside panel should be treated as a sub-panel or not. Treating it as a sub-panel seems reasonable, but none of my books refer to this specific setup...

I should also mention that the new panel and outside meter / combo unit unit passed inspection, though I wasn't inspired by the electrician's other work...


Originally Posted by syperk
B) And if the neutral and grounding bars in the inside panel ARE supposed to be disconnected, shouldn't the left hand grounding bar in the inside panel be bonded to the panel case with the bonding screw? It's currently insulated as far as I can tell.
Originally Posted by nab
Usually the ground bar mounts directly to the tub. If it doesn't, then yes, it needs to be bonded to the tub. The neut must be isolated at this point.
I think this particular panel is designed to be "convertible" i.e. it can act as a main or a sub-panel. In the main panel configuration, the grounding bar and the neutral bar are tied together, and then bonded to the case with a green bonding screw in the right hand bar. In the sub-panel configuration, the tie connector is removed and the bonding screw is moved to the left bar.

Originally Posted by nab
A question on the outside panel:

Are you sure the line side power is not backfed through the 200 amp breaker. If the inside panel is then fed from the bus as feed through, this would then make that acceptable but the inside panel still needs to be treated as a sub
If I understand you correctly, that's the setup I have.


OK, so basically it appears that I need to remove the tie between the neutral and grounding bars in the branch circuit (inside) panel, and then find a bonding screw from somewhere to bond the grounding bar to the panel case.

I probably then also need to connect the water pipe ground to the outside panel grounding bar rather than the inside grounding bar (though this bar is connected directly via a wire to the outside grounding bar, so it seems a teensy bit pedantic...


Cheers,

Simon
 
  #4  
Old 08-23-06, 06:52 AM
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I agree with all NAP has said. I think though you are misunderstanding the 200 amp panel fed from the meter main outside.
I also agree that the water line gec should not be attached at this panel it should come from the main disconnect service equipment outside. The way it is now it would appear the inspector is allowing the conduit to act as the gec between the outside main and the inside panel then to the water pipe. but I dont believe this is what you would want.
You have a 200 amp seimens main breaker panel inside. The neutral/ground bar design varies. But generally seimens has a split neutral design. It sounds like this is what you have. It may have a flat metal strap that connects the two bars and a green bonding screw that would go in next to one of the big lugs. My guess is that since the electrician installed a ground bar on the panel tub/can there is also a metal strap that is connecting the two neutral bars that sit on insulated stand-offs on each side of the breaker busses. So you have three bars in the panel. The ground bar is not electrically connected to the two neutral bars because the green screw is not installed. Give us the panel model number you have off the spec sheet on your load centers door and we can check the design.

I am concerned that you are going to have a problem with not having enough holes on a small ground bar to accomodate a 40 circuit panel but that can be fixed in a couple ways. The one you have may be fine for your needs. Thats why the design of the panel would be helpful to understand.

At anyrate let us now if your design has that strap between the two neutral bars. Only reason I think this information is important is so you/we understand how that seperation of neutral and ground works for your particular 200 amp panel. Most likely your fine with the set up as it is.

Remember when you go to wire your branch circuits that you will not have bare equipment grounds and neutral wires landing on the same bar. The grounds will go to the grounding bar mounted or bonded to the can the neutrals to the bar/bars on the insulated stand-offs.

"Convertible" means it can be either main lug or main breaker. Not main panel or sub-panel. It can however be wired as a sub-panel.

I'm a little confused on how they did the feed to the inside panel. You say the 100 amp panel is fed from a breaker in the outside main. So could you explain how that differs for the new 200 amp panel. You say feed thru...just trying to get that clear in my head.

If you are correct in your description on the panel bonding design I would check to see if it has locations on each side of the can to mount grounding bars. Pairs of predrilled holes are usually in two locations on both sides of the seimens 40 circuit panels. If so I wouldnt remove the metal strap bonding the bars and I wouldnt install the bonding screw. I would just install another ground bar on the side of the panel opposite the one the electrician installed. This will make wiring the panel much easier. You will have two neutral bars and two ground bars located so you can land your grounds an neutrals for one bank of breakers to its side and the other bank the other side...ie...you wont have to have long ground wires crossing over to the single ground bar the way it is now.

Roger
 

Last edited by Roger; 08-23-06 at 07:35 AM.
  #5  
Old 08-23-06, 07:47 AM
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The panel door has 4 numbers on it:

G4040B1200
G4040B1200CU
G4040L1200
G4040B1200CU

There's no particular indication as to which one I actually have, though since I see mainly copper inside, I'm guessing that it's one of the two "CU" options. And since the unit includes a 200A breaker that controls the whole panel, does that mean that it's a "Main Breaker" rather than a "Main Lug" configuration? So, G4040B1200CU?

There's some information on these load centers at:

http://www.sea.siemens.com/resident/docs/RPBR-S0007-1003.pdf
http://www.sea.siemens.com/speedfax05/05%20Speedfax/05Speedfax_01/01_15-16.pdf

The two neutral bars are connected via a solid core copper wire that looks like it's made for the job. It's about a 1/4" thick - though this is still substantially thinner than the multistrand neutral wire supplying the panel. There is no bonding screw present.

The "small" separate grounding bar (to which the incoming grounding line from the service entrance is attached) is attached directly to the case and contains 23 spare terminals. I'd assumed that it couldn't be the main grounding bar since it didn't have enough spare terminals for all the circuits I need to install. However, if I'm allowed to double up on grounds then I guess I can use that. Or as Roger suggests, I could install a second grounding bar on the right hand side of the cabinet. Now that I look I see there are indeed mounting holes for that.

So, perhaps everything is fine, except for the water pipe grounding issue? I'll install another grounding bar (is the electrical connection through the case sufficient or should this be wired to the other ground bar?) When I run branch circuits I'll run the white neutral wires to either of the two neutral bars (which now have way more than enough spare terminals between them!), and the grounds to one of the two grounding bars.

Please let me know if this is right.

Thanks again for your advice and time on this!

Cheers,

Simon
 
  #6  
Old 08-23-06, 08:11 AM
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In answer to Roger's question about how the supply to the new 200A panel differs from the supply to the old 100A panel:

- The external cabinet is fed from the meter via thick wires. The two hot wires are fed (I think "back fed" might be the right term here) into a large 200A 2 pole breaker at the top of the outisde panel. The 200A breaker is labeled "service disconnect".

- The outside panel has a few breaker slots and then some big lugs at the bottom of the two hot legs, which are referred to as "feed through lugs" on the circuit diagram on the door. These feed through lugs are what supply the new inside 200A panel.

- In one of the breaker slots in the outside panel is a 100A 2 pole breaker that supplies the old 100A inside panel. Once the 100A panel is no longer needed, I'll remove this breaker.

Does this sound reasonable?

Cheers,

Simon
 
  #7  
Old 08-23-06, 08:27 AM
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If the 200 amp C-B located in an out-door will de-energize ALL power to ALL of the interior wiring when moved to the "Off" position, then this C-B is the Service Dis-connecting Means.

The Grounding Electrode Conductor clamped to the water-service line is required to be connected to the Grounded Service Conductor (GSC, Neutral) at the point where the GSC terminates in the Service Dis-connecting Means enclosure.

From your description, the 200 amp Feeder between the Service Dis-connect and the interior 200 amp C-B panel includes a Equiptment Grounding Conductor ( EGC ).

"Bonded" together in the C-B panel are--- The Feeder EGC-- the EGC's of the cables that extend from the C-B panel--the metallic surface of the C-B panel enclosure.

All Neutral terminations in the C-B panel are required to be "Ground-isolated", i.e., insulated and seperated from any and all connections to Ground.

Good Luck, & Learn & Enjoy from the Experience!!!
 
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Old 08-23-06, 08:29 AM
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- The external cabinet is fed from the meter via thick wires. The two hot wires are fed (I think "back fed" might be the right term here) into a large 200A 2 pole breaker at the top of the outisde panel. The 200A breaker is labeled "service disconnect".

That's what I was talking about.

In your first post, it sounded as if the panel inside was not controlled by the breaker in the service panel outside. Now you say it is. If this is so, everything else is a subpanel and the grounds and neuts have to be seperated anywhere past the service panel.

There is nothing wrong with the lugs on the buss at the service panel because the breaker will turn off the power to the buss. This is a common method used with a panel that is not designed to have 1 main breaker.

The water pipe must also be tied into the service panel and not a sub.
 
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Old 08-23-06, 08:36 AM
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Thanks to everyone, particularly Nap and Roger, for clearing up my confusions on this issue, and for correcting my incorrect assumptions about how my panel setup works!

Cheers,

Sy
 
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Old 08-23-06, 09:04 AM
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There are no "back-feed" connections in this hook-up.

An example of "back-feed" is when an E-P generator is connected to the house wiring with the Main-breaker in the "On" position.

With the Main-breaker "On", the generated voltage is both a "direct-feed" to the interior wiring, and a "back-feed" to the utility power-connections via the Main-breaker, the meter-connections, and the exterior Service Conductors.
 
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Old 08-23-06, 09:32 AM
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It is commonly termed "back fed" in my area when speaking of this type of connection. The power actually transfers from the terminals of the breaker- through the breaker- to the buss rather than the typical buss-through breaker-to terminals.

You can call it whatever you want but we call it back fed here.

I suppose it may be used to indicate "fed backwards (throught the breaker)" since that is what is happening.

You can call it whatever you want but we call it back fed here. Any sparky I talk to will understand what is meant using this terminology when describing a situation such as this.
 
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Old 08-23-06, 09:41 AM
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Yep, it is a back fed breaker around here too...

FYI:

G4040B1200CU

G = (Indoor rated only)..... W = Wet location (outdoors)
40 = max number of 1 inch full size breakers...(no dual or tandem single pole breakers will fit this panel)
40 = max. number of circuits.
B = Main Breaker
1 = single phase
200 = panel amp rating (main breaker size)
CU = copper busses.....if left blank = aluminum busses


You do not have to connect the ground bars with a wire... the
metal of the panel will bond the the ground bars.
 
  #13  
Old 08-23-06, 11:14 AM
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Originally Posted by Roger
FYI:

G4040B1200CU

G = (Indoor rated only)..... W = Wet location (outdoors)
40 = max number of 1 inch full size breakers...(no dual or tandem single pole breakers will fit this panel)
40 = max. number of circuits.
B = Main Breaker
1 = single phase
200 = panel amp rating (main breaker size)
CU = copper busses.....if left blank = aluminum busses
That would seem to be what I have - thanks for the clarification!

OK, one more question: I understand that I'm limited to 40 circuits in this panel. Am I actually prohibited from using half-size breakers at all? The reason I ask is that I went and bought a few quad breakers the other day - 4 half-size breakers in a package with the center two bridged together to act as a 2-pole breaker. If I'm not supposed to be using these in my panel, I'll go back to the store and replace them with full size breakers. Do 2-pole breakers count as two circuits toward the 40 circuit limit?

Thanks,

Simon
 
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Old 08-23-06, 11:27 AM
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a two pole breaker count as taking up two spaces.

classified breakers. (those listed by the mfg as being ok to put in that panel) can increase the count. The answer is to ck with the panel mfg to see if those breakers are classified for use in that panel.
 
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Old 08-23-06, 12:01 PM
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Look on the breaker face it will give the type breaker on the listing label. Now go to your panel cover on the spec. sheet it will list the breakers the panel will except. If a QT type breaker and panel sheet says QT in its listing then the breaker fits the panel. Usually sheet says something like....Use only QT,QTP,QTL...etc...these must match exactly with the breaker.
Do not just go to the panel and see if it fits, that isnt good enough.
Though you could get a feel as to how to install it
if it is listed for the panel. By that I mean a lot of people just think the things just fall right in. It can take a little effort Some times.
As JW says the breaker will take up 2 one inch spaces.
 
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Old 08-23-06, 02:00 PM
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This is my concept of the term"Back-feed" as applied to C-B connections--

A 2-pole 100 amp C-B is inserted into a "Main Lugs" panel, and the Service/Feeder Conductors terminate on the C-B terminals.The terminals of all the other C-B's in the panel are "Load" terminals, but the terminals of the 100 amp C-B are "Line" terminals- a "reverse", or "back-feed" arrangement for the 100 amp C-B which connects to the bus as the others C-B's do.

AS best I know, the 200 amp panel under discussion is a "Main-breaker" panel with lugs on the busses for terminating 200 amp Feeder Conductors from an interior panel. A 100 amp breaker which is inserted into the panel protects a 100 amp Feeder to a 2nd panel.
 
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Old 08-23-06, 02:11 PM
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OK paattbaa. it seems you are right. I apparently read over the fact that he did indicate it to be a main breaker.
When th OP posted this:

"This is my understanding if the 200A panel is treated as a sub-panel, but maybe it's treated as a main panel since it's supplied by feed through terminals from the outside panel?"

I took it that he was dealing with an MLO panel and the 200 amp interior panel was not controlled by the 200 amp breaker in the main panel.

Only later did he state that it does in fact control the power to the interior panel. My misunderstanding.
 
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Old 08-23-06, 07:41 PM
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Red face

I was wrong one time back in 1972 looks like I am wrong again on this being a back feed.....maybe I'll go another 34 years before I am wrong again.....

Roger
 
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Old 04-16-07, 08:42 PM
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Just a word of point.

Hi all,I was just reading thru this thread,and got a good bit of usefull info.At the end,I chuckled,at the wording of,it being 34 years sence he was wrong,and how it may be another 34 before he's wrong again....... It brought to mind a thought..... "Considering the livelyhood of being a sparky,you don't always get the chance to be (wrong) a second time." keep up the good work.
 
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Old 04-16-07, 10:45 PM
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Just a feeble attempt at humor but now that I think about it I wasn't wrong I was mistaken.

roger
 
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