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View Full Version : Proper bonding? 2 disconnects, 2 main panels, 1 generator, 3 troughs.


jcrack_corn
February 28th, 2011, 01:07 PM
i figure it is best to ask this neutral-ground bonding/box grounding question by working backwards. I do have pictures of all boxes if needed.

all house circuits come into 2 ge 200 amp main panels with main breakers. (these panels were the old service disconnect/fed from meter). Neutral/ground bonding bar is in place in both boxes, and both boxes are bonded to ground.

from each ge 200 amp box there are 3 2/0 (l1, l2, N) that go to generator txfr switches/new service entrance disconnects (one is an ATS for critical loads, one is a manual transfer for air conditioners).

In EACH of those boxes neutral bar is also bonded to ground and the box's (but there is NO ground wire leaving these boxes) -- bonding is in place to bond the box's.

from here each box has 3 2/0's leaving (L1, L2, N). The L1/L2's go to the main trough where they are tied to the 400a service). Each 2/0 neutral (which is also still carrying ground from the original main panels) goes to a 2nd trough (new) below the txfr switches where they tie into a large bus bar that is bonded to the box. This bus bar his those 2 neutrals, the generator neutral, the generator ground (there is NOT a second grounding point at the generator except for chassis) and 2 2/0 neutrals that go to the original trough.

Now back in the original trough we have the 2 2/0 neutrals from the buss bar in the new trough, the service neutral, and the house ground.

There is a 3rd trough/wiring box for the generator that only has a small 2 space bus bar bonded to the box and it receives the generator ground (not the generator neutral, which is bonded at the new trough to ground via the buss bar).

I cant see how there is any problem in this (and no one has suggested their is) I just want to make sure that the bonding in the original panels is fine as the transfer switches are just disconnects. after the main panels there is only one path for neutral/ground UNTIL you get to the original trough at which point neutral can return via service neutral or ground rod.

So if any HV hits the box, all boxes are bonded, if the service neutral goes open, there is 1 path back to ground. I guess the only potentially dangerous fault is if N is disconnected at any point (main box 1, main box 2, ATS, manual ts) then the box could go live because there is no neutral/ground path then.....but i think that is normal and unexpected.


neutral
ground (seperate) --------------> box1/box2(N/G bond)----->ATS/Manual txfr (no ground wire, neutral/G still bonded)---------->trough buss (bonded to box, no ground) ----------> old trough buss (bonded to box, bonded to ground rod) ---------> service neutral.

suemarkp
February 28th, 2011, 07:32 PM
Technically, I think this is in violation. But first, some questions:

Are the transfer switches labeled "Suitable for use a Service Equipment"?
Do the transfer switches have over current protection built into them?
Are the transfer switches next to each other?
Are they next to the main panels, and on the same side of the wall?
Are the gutters and wiring methods between meter, switches, panels, and gutters ferrous metal, aluminum, PVC, or cable?

I believe your transfer switches should be your Service Disconnects. After this, you should have 4 wires to the main panels and not 3. This would also require that the bond be removed in the main panels. To me, this is minor issue if all the transfer switches and main panels are close to each other. But code says you stop bonding neutral at the Service Disconnect.

Your wire size should have been 3/0 and not 2/0 because you can only use 2/0 when it carries the full load of a dwelling. Yours are only carrying half.

I'm a bit lost with all your gutters, but it sound like there is one that just has neutrals. If the gutter and conduits feeding it are ferrous metal, this is in violation. All conductors of a circuit must travel together. Having the neutral off on its own will cause inductive heating between that gutter and the ones with the hot wires. So the neutrals should all be in the same gutters as the ungrounded conductors.

jcrack_corn
February 28th, 2011, 09:30 PM
Technically, I think this is in violation. But first, some questions:

Are the transfer switches labeled "Suitable for use a Service Equipment"?

yes, both are service entrance equipment

Do the transfer switches have over current protection built into them?

The ATS has 200a breaker for service entrance and 200A for generator.
The manual has none, but the generator has 65A, and the panel the manual switch feeds has 200a main breaker.

Are the transfer switches next to each other?
Are they next to the main panels, and on the same side of the wall?

All 4 panels are surface mounted right next to each other on same side of the wall...about 6 inches between each one.

Are the gutters and wiring methods between meter, switches, panels, and gutters ferrous metal, aluminum, PVC, or cable?

All boxes are metal. All raceways/conduits are PVC between all metal boxes. Every box is isolated from the other one by PVC conduit.

I believe your transfer switches should be your Service Disconnects. After this, you should have 4 wires to the main panels and not 3. This would also require that the bond be removed in the main panels. To me, this is minor issue if all the transfer switches and main panels are close to each other. But code says you stop bonding neutral at the Service Disconnect.

This was my main concern and I came to the same conclusion as you. Not sure what i want do do about it...pretty easy fix so probably just fix it.


Your wire size should have been 3/0 and not 2/0 because you can only use 2/0 when it carries the full load of a dwelling. Yours are only carrying half.

Interesting...this is just how it was....AL 600 kcmil enters 400a (320) base lugs. From there 2 400 kcmil coppers go to the first (original gutter) and each of them goes to a large insulated splicing lug. From that lug there are 2 2/0 coppers.

So if there was 1 400 amp panel this would be fine right, but since there are 2 200a disconnects from that point on it should be 3/0?

Any exceptions to this rule as I think many 400a services are split into 2 200's? Again, not a big deal, I can run new 3/0.



I'm a bit lost with all your gutters, but it sound like there is one that just has neutrals. If the gutter and conduits feeding it are ferrous metal, this is in violation. All conductors of a circuit must travel together. Having the neutral off on its own will cause inductive heating between that gutter and the ones with the hot wires. So the neutrals should all be in the same gutters as the ungrounded conductors.

no, all gutters have all circuit wires in them (so the first gutter is directly off the meter with L1, L2, N.....that feeds gutter 2 via 6 2/0 wires (L1, L2 / L1, L2, N1, N2)....and so on and so forth....and as previously mentioned all gutters are metal, all conduit pvc.

I will post the pictures up in the next day or two for clarity.

So far:
1.) unbond main panels, feed grounds from ATS and Manual TS to main panels, keep ATS and Manual TS bonded.

2.) convert all 2/0 to 3/0 (from service entrance to each transfer switch, then from each transfer switch to each 200a main panel).

http://img148.imageshack.us/img148/1018/mainpanels.jpg
http://img251.imageshack.us/img251/7695/transfersi.jpg


the main panels would be on the left, the switches to the right of them....i would need to upsize the conduit between the two troughs if going to 3/0. And you are seeing the edge of the meter base to the left of the main panels.

The wire nuts you see in the main panel on right are due to moved a/c circuits to the left panel (all a/c circuits there), the main panel on left now supplies the two interior house sub panels for interior circuits (you can see the 90a on the left bus bar in the right panel was previously in the left main panel, there was plenty of slack to move it over. Boxes were used as raceways in this case as there was no other alternative and I believe that is allowed in such cases. The wire nuts were taped for added security, rookie mistake.

suemarkp
February 28th, 2011, 09:50 PM
The requirement for 3/0 is because you can't use table 310.15(B)(6). Normal size wire for 200A is 3/0 copper. If you had a 400A transfer switch and panel, you could use 400 KCMil copper or 600 KCMil AL for everything. As soon as the entire house load splits, you have to change to table 310.16.

I'm not so sure the 200A panel fed from the manual transfer switch is "immediately adjacent". Would be a judgement call by the inspector.

Where is your ground electrode conductor? A good place to put it is in one of your Service gutters (line side of service disconnects). This way, you don't have to run grounds to each service disconnect.

I'm not so sure the gutters are legal. When using conductors larger than #4, you need 6X the conduit diameter to the opposite box wall if the wire bends, and 8X if the wire goes straight through. The only way to mitigate these distances is to put a conduit in the back wall, then there is no limit to the distance from a removable cover.

I'm not totally sure of the ferrous rule if the conduits are PVC. I think it still applies because two adjacent ferrous boxes have different conductors of the same circuit. I'd try to keep neutrals with ungrounded's whenever possible.

Finally, you may not need to upsize conduits sizes (which will keep the gutter size problem from getting worse). A conduit nipple, which is defined as being 24" or shorter, doesn't have to abide by the normal 40% fill rules.

jcrack_corn
March 1st, 2011, 06:34 PM
the ground is in that older gutter on the left, in that buss bar.....so the plan currently is:

Upgrade to 3/0 in all places where 2/0 is. Easy job except for meter pull....but i can use the disconnects to at least get the main panels done first.

Run grounds to each main panel, remove bonding bar in each main panel. The grounds from each main panel will run to ground buss in each service disconnect. The service disconnects will continue to have their neutral-ground bonds in place.

The 2/0 neutrals from each disconnect will also be upgraded to 3/0 and that will run to the buss bars in the gutters (which is where the ground rod connects to).

Neutrals always run with L1/L2 in all cases now and with the proposed changes.

Forgot about the nipple rule/40% fill...that will save some time!

Regarding the conduit diameter rule in gutters...can you explain more? I believe i used 2.5" nipples...how would any gutter ever be code if having a top exit? That would be fine for the side entrance/exits (24" gutters)....please clairify.

AND THANKS A TON!

BTW I did this job myself about a year ago because 4 electricians came out, 2 said they didnt want the job and 2 said no problem and never called back. Can you comment on the overall cleanliness of the wiring/neatness...any other comments?


The requirement for 3/0 is because you can't use table 310.15(B)(6). Normal size wire for 200A is 3/0 copper. If you had a 400A transfer switch and panel, you could use 400 KCMil copper or 600 KCMil AL for everything. As soon as the entire house load splits, you have to change to table 310.16.

I'm not so sure the 200A panel fed from the manual transfer switch is "immediately adjacent". Would be a judgement call by the inspector.

Where is your ground electrode conductor? A good place to put it is in one of your Service gutters (line side of service disconnects). This way, you don't have to run grounds to each service disconnect.

I'm not so sure the gutters are legal. When using conductors larger than #4, you need 6X the conduit diameter to the opposite box wall if the wire bends, and 8X if the wire goes straight through. The only way to mitigate these distances is to put a conduit in the back wall, then there is no limit to the distance from a removable cover.

I'm not totally sure of the ferrous rule if the conduits are PVC. I think it still applies because two adjacent ferrous boxes have different conductors of the same circuit. I'd try to keep neutrals with ungrounded's whenever possible.

Finally, you may not need to upsize conduits sizes (which will keep the gutter size problem from getting worse). A conduit nipple, which is defined as being 24" or shorter, doesn't have to abide by the normal 40% fill rules.

jcrack_corn
March 2nd, 2011, 11:06 PM
ok...so i've read up on the NEC pull box rules and what if have come up with is:

the old gutter is legal, it is a straight pull. Service entrance conduit is 3"...

3 x 8 = 24 inches. Box is 24 in...so we are good there.

The new gutter is not legal.

Again, cant remember if i used 2 or 2.5 inch nipples (too dark to go look right now)...but with 2" (i believe that is what it is) then:

2 x 6 = 12 + 2 = 14 inches (using the top of the gutter with 2 conduits)

2 x 6 = 12 inches (using either of the other sides of the gutter with 1 conduit)

So my minimum box size is 14 x 12...that box is 24 x 6.

Not a big deal....i will get a 24 x 1X (bigger than 12) so all my nipples line up as they are now and i can move over that first nipple to get it 15 inches from the other nipple (i will likely upsize that short run to 2.5 inches when i go to 3/0, even though i dont have to, it will be easy).

Sound good?

suemarkp
March 3rd, 2011, 07:02 AM
Yep. Forgot about this post yesterday and to go read about box sizing. But it sounds like you found it and sized it right.

You can most likely leave your neutrals at 2/0 if that will save some money (reuse some of that 2/0 you're replacing). Hardly any load calculation would require a full size neutral in a service or feeder -- only if every single load was 120V.

I can sympathize with having to do it yourself. I inquired with a few electricians for my 400A service mod. Most didn't want it, a few were grossly over priced and I think I knew the code book better than they did.

jcrack_corn
March 3rd, 2011, 03:27 PM
Yeah..almost all the circuits in the house are 240v, all room circuits are multi-wire branch circuits....so i imagine the neutral is fairly benign. I have considered leaving it 2/0.

however, I have done some research and have a call into my inspector because it seems 2/0 feeders from the 400 kmcil to each panel is legal here. Should have confirmation tomorrow. The loads are certainly acceptable for the 2/0 for now, so I'm not overly concerned, but will make it right. should need about 60 feet of 3/0 and its 4.55/lft right now from my supply house...so not an expensive fix, just have to get the meter pulled for a day. And that will make doing the box change easy all at the same time.

THANKS!

Yep. Forgot about this post yesterday and to go read about box sizing. But it sounds like you found it and sized it right.

You can most likely leave your neutrals at 2/0 if that will save some money (reuse some of that 2/0 you're replacing). Hardly any load calculation would require a full size neutral in a service or feeder -- only if every single load was 120V.

I can sympathize with having to do it yourself. I inquired with a few electricians for my 400A service mod. Most didn't want it, a few were grossly over priced and I think I knew the code book better than they did.

jcrack_corn
March 4th, 2011, 04:47 PM
FYI inspector says 2/0 feeders are ok for residential in my area with a 400 amp service feeding 2 200 amp panels. his opinion is that it falls under the exception table for service feeders. He said it is not allowed for commercial here and in both cases loads should be calculated.

My list is now greatly shortened to running grounds to both original main panels and unbonding both panels (will ensure that green bonding screw IS in place on the ground bar and NOT on the neutral bars, to keep case bonded to ground).

Will change the gutter to a 24x16 or similar when I get a chance...want it to be right, but not to concerned about my bends at this point and my fill capacities are all good. When I do so, I will have to pull the meter anyway, so may just run the 3/0 for fun then at least to the disconnects....then can upgrade at my convenience from there.

thanks for the help!