Trough fed twin service bonding and grounding

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ShauwnC

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Location
Fairfax virginia
We failed an inspection today on grounding and the inspector seemed unsure and I believe he made a bogus call. Here is the setup. We replaced panels on a trough fed service. Old panels were FPE and one was a 200 amp and one was a 100 amp that fed an old electric furnace. We installed 2 new 200 amp panels in place of the old equipment. We had a 320amp/ 400amp meter with one set of conductors( not parallel or double lugs ) from load side of the meter to the trough fed with 250 mcm I believe. For a full picture I tapped in the trough (clear taps) and fed both panels with 4/0 seu. From my electrodes I went to the ground plate/bar in the trough and then to panel #1 and then to panel #2. the GEC IS #6 copper and wire is uncut/continuous. We also ran #4 copper from each panel to the main water shut off valve. The inspector was probably confused and was thinking of the trough like a disconnect but he said a couple of different things and finally settled on checking with his chief inspector. He got back to me at the end of the day and he said the chief wanted the GEC to terminate in the trough and the supplemental GEC to the water pipe to also go to the trough. Bond screws in ( which they already were ) and that's it. What do you guys think of this as this does not seem correct to me. We have done trough fed services before and have never relied on only a bond screw and a seu cable to bond a panel.
 
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augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
If I follow correctly the only problem I see is that, IMO, the conductor from the panel to the trough would need to be #4 based on the 4/0AL service conductor.
 

ShauwnC

Member
Location
Fairfax virginia
Are you saying that the # 4 to the water pipe and #4 from each panel to the trough as well? If so are you saying the #4 from the panels doesn't have to be continuous? My question is doesn't the way it is currently set up satisfy the intent of the code? Would the #4 from the trough to the panels be considered a bonding jumper or a ground tap? Ugh this one is a pain.
 

RUWired

Senior Member
Location
Pa.
He got back to me at the end of the day and he said the chief wanted the GEC to terminate in the trough and the supplemental GEC to the water pipe to also go to the trough. Bond screws in ( which they already were ) and that's it. .

Sounds like the chief inspector has you following the 250.64 (D)3 method. You were trying to apply D1,2 and 3 all together.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
There are a few details missing such as the wiring method being PVC or metallic conduits which will effect the bonding but all metal raceways and service enclosures would need to be bonded.
Your #4 from each panel to the water line is IMO Code compliant.
The #6 to the ground rod likewise.
From your post one would assume the trough is metallic and as such needs to be bonded. Unless that bonding is completed using metallic conduits with grounding locknuts or bushing as applicable, it would need a bonding conductor With your 250 (cu?) from the meter that would require a #2 bond to the wireway from the 250 neutral. A bond from each panel to the trough could possibly be acceptable to the AHJ but if that method was used I would think it would need to be based on the 4/0AL as a minimum and that would require a #4 Cu
 

ShauwnC

Member
Location
Fairfax virginia
The trough is metallic. From the trough we are using 4/0 service entrance cable aka seu. Two hots and a bare in a prepackaged cable. I don't argue that the GEC was undersized for the 250 aluminum as that should be #2 copper per 250.66. I am questioning his request to bring both primary and secondary GEC wires to the trough and stop them there. The only conductor bonding the equipment ( the two panels with main breakers ) is the bare conductor in the service cable. I am having difficulty interpreting 250.64(D)(2) ! Does this article allow the bare conductor I mentioned to double as both the grounded conductor and the GEC? I'm also having difficulty with 250.64(D)(1) as that states GEC taps shall be installed. I want to get this right and not just do what the AHJ says. I do remember a few years back another job with a tap box and a six throws of the hand 1600 amp service the inspector made us do the same thing but the only difference was the feeder cables were in pvc conduit and were insulated conductors. If I recall correctly he said we need to do it that way due to double grounds will create"ground loops". Any help here is appreciated. I'm Just trying to understand and comprehend.
 

HumTum

Member
Location
United State
want to get this right and not just do what the AHJ says. I do remember a few years back another job with a tap box and a six throws of the hand 1600 amp service the inspector made us do the same thing but the only difference was the feeder cables were in pvc conduit and were insulated conductors.



____________
Arslan1
 

jap

Senior Member
Occupation
Electrician
We failed an inspection today on grounding and the inspector seemed unsure and I believe he made a bogus call. Here is the setup. We replaced panels on a trough fed service. Old panels were FPE and one was a 200 amp and one was a 100 amp that fed an old electric furnace. We installed 2 new 200 amp panels in place of the old equipment. We had a 320amp/ 400amp meter with one set of conductors( not parallel or double lugs ) from load side of the meter to the trough fed with 250 mcm I believe. For a full picture I tapped in the trough (clear taps) and fed both panels with 4/0 seu. From my electrodes I went to the ground plate/bar in the trough and then to panel #1 and then to panel #2. the GEC IS #6 copper and wire is uncut/continuous. We also ran #4 copper from each panel to the main water shut off valve. The inspector was probably confused and was thinking of the trough like a disconnect but he said a couple of different things and finally settled on checking with his chief inspector. He got back to me at the end of the day and he said the chief wanted the GEC to terminate in the trough and the supplemental GEC to the water pipe to also go to the trough. Bond screws in ( which they already were ) and that's it. What do you guys think of this as this does not seem correct to me. We have done trough fed services before and have never relied on only a bond screw and a seu cable to bond a panel.

It doesn't so much sound like the inspector or you are incorrect as much as it sounds like the Inspector wanted the Grounding Electrode conductor and bonds to the water pipe all terminated at one spot which was in the guttern whearas you terminated them in a different location which I don't see a problem with either.

I would have probably brought the GEC to the meterbase and bonded the neutral there if it was considered accessible,
Let the Neutral do it's thing for both panels.
Bond both panels neutral bars to the can with the bonding screw since we have to, and if the trough was already bonded with locknuts, bonding locknuts or bushing have taken a bond wire from the Neutral/Ground bar in each panel to the Water pipe, and probably gotten flagged just like you did. :)
 

RUWired

Senior Member
Location
Pa.
I don't argue that the GEC was undersized for the 250 aluminum as that should be #2 copper per 250.66.
Table 250.66 Shows a # 4 awg cu. for 250kcmil AL conductors

shauwnC said:
I am questioning his request to bring both primary and secondary GEC wires to the trough and stop them there.
This is ok per 250.64(D)3 (common location)


shauwnC said:
I am having difficulty interpreting 250.64(D)(2) !
250.64(D)2 (individual Grounding electrode conductors) is saying individual GEC's from the electrode(s) go to each individual service disconnect /panel separately.
shauwnC said:
I'm also having difficulty with 250.64(D)(1) as that states GEC taps shall be installed.
250.64(D)1 (common grounding electrode conductors and taps)is saying you can run a common GEC from the electrode(s) to a location and tap off that GEC to the individual service disconnect/panels separately.

Rick
 

HumTum

Member
Location
United State
want to get this right and not just do what the AHJ says. I do remember a few years back another job with a tap box and a six throws of the hand 1600 amp service the inspector made us do the same thing but the only difference was the feeder cables were in pvc conduit and were insulated conductors.



 
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