NEC 250.80, 250.92

[hhsting]

Attached sketch shows 4# 500kcmil service conductors from utility CT meter cabinet into trough. From trough cable 4#500kcmil is tapped 4#3/0AWG into each 200A fused service disconnect. The trough does not have any neutral bus, any phase bus only phase and neutral cables.

The two service disconnects 200A has main bonding jumper shown attached sketch and grounding and bonding method is NEC 2014 section 250.64(D)(1) . Each service disconnect is tapped with #4 AWG grounding electrode conductor tap which is routed in same conduit that contain 4#3/0 AWG phase and neutral conductors each 200A fused disco conduit to 0.25 inch x 2 inch ground bus bar in the trough.

The ground bus bar inside trough has grounding electrode conductors to steel, water pipe underground, concrete encased electrode. Their is also bonding jumper from ground bus bar to trough.

Question:

1. NEC 2014 section 250.80 says all grounding and bonding supply side need to be by neutral. I don’t have neutral bus only neutral cable which is tapped to provide conductors for service disco. How can one place bonding jumper from neutral cable to trough?

2. Would bonding jumper from trough to ground bus bar acceptable or does it have to come from neutral cable?

3. If neutral cable has bonding jumper to trough enclosure then would ground bus bar also need to have the bonding jumper to trough enclosure?

4. How does one do grounding and bonding in trough with service phase and neutral conductor and ground bus bar for 250.64(D)(1) in trough line side of service disco based on NEC 2014 250.80 or 250.92 or some other section? If other section then which one?

 

[augie47]

Personally I'd find it simpler IF you were going to use the ground bar, to tap by neutral with a 1/0 to the ground bar, bond my neurals in the disconnects and do all my bonding jumpers and electrodes from the bar,

 

[hhsting]

Personally I'd find it simpler IF you were going to use the ground bar, to tap by neutral with a 1/0 to the ground bar, bond my neurals in the disconnects and do all my bonding jumpers and electrodes from the bar,

Right that would be 250.64(D)(3). However the designer wants to do it with 250.64(D)(1) and as mentioned in post#1.

 

[roger]

Just install a ground bar in the trough.

Roger

 

[electrofelon]

Just install a ground bar in the trough.

Roger

If I am understanding correctly, there already is a "bar" in the trough, but it is a GEC busbar, and there is a SSBJ from the trough to this GEC busbar. So the GEC tap from the service disconnect to the GEC busbar is ALSO BEING USED as a SSBJ? I dont see anything that says a conductor cant be both a SSBJ and a GEC tap. The sticky thing is the NEC does not direct us how to run SSBJ's with multiple service disconnect enclosures.

 

[electrofelon]

Here is the way I see it: How to assure the trough is properly bonded is what the issue is here. It boils down to whether the TROUGH->SSBJ to GEC busbar->GEC tap to service disconnect ground/neutral bar/MBJ is acceptable. What is the wiring method between the trough and the discos? IF its metal conduit* complying with 250.92(B) then the other stuff doesnt matter.

*but then the GEC taps would need to be bonded to each end of the raceway

 

[hhsting]

Here is the way I see it: How to assure the trough is properly bonded is what the issue is here. It boils down to whether the TROUGH->SSBJ to GEC busbar->GEC tap to service disconnect ground/neutral bar/MBJ is acceptable. What is the wiring method between the trough and the discos? IF its metal conduit* complying with 250.92(B) then the other stuff doesnt matter.

*but then the GEC taps would need to be bonded to each end of the raceway

The system is 208/120V three phase and yes the wiring methods between trough and the disco is metal conduit.

 

[hhsting]

Here is the way I see it: How to assure the trough is properly bonded is what the issue is here. It boils down to whether the TROUGH->SSBJ to GEC busbar->GEC tap to service disconnect ground/neutral bar/MBJ is acceptable. What is the wiring method between the trough and the discos? IF its metal conduit* complying with 250.92(B) then the other stuff doesnt matter.

*but then the GEC taps would need to be bonded to each end of the raceway

Yes their already is ground bar. 250.80 says everything should be bonded to trough via neutral however I have ground bar bonding trough not neutral to enclosure and GEC tap to ground bus bar which via MBJ in service disco gets bonded to neutral. See post #1 attachment. I am not sure if SSBJ 250.92 would apply. How should the trough be grounded and bonded correctly?

 

[electrofelon]

250.80 says everything should be bonded to trough via neutral

That's not really what 250.80 says. Reread it, then reread my post #6. Spend a few minutes reading it several times and thinking about it, then feel free to come back and ask more questions. I didn't really say it in post 6 I guess but I can't think of a violation, other than the code's vagueness on SSBJ's with multiple service enclosures.

 

[electrofelon]

250.80 says: “Metal enclosures and raceways for service conductors and equipment shall be connected to the grounded system conductor if the electrical system is grounded or to the grounding electrode conductor for electrical systems that are not grounded.

Exception: A metal elbow that is installed in an underground nonmetallic raceway and is isolated from possible contact by a minimum cover of 450 mm (18 in.) to any part of the elbow shall not be required to be connected to the grounded system conductor or grounding electrode conductor.”

In my case trough is connected to ground bus bar. How is that in compliance with NEC 2014 section 250.80?

It IS connected to the grounded conductor, just thru the GEC busbar and the gec tap. I don't really see anything in the code that says it needs to connected "directly" to the grounded conductor. Of you are the AHJ I guess you just have to make the call an whether that is the intent of the code.

PS I am copying this to the regular forum. Please keep the discussion there so others can give their interpretation.

 

[electrofelon]

By the way mods please do not close this thread prematurely, I think it is a good and interesting question

 

[hhsting]

It IS connected to the grounded conductor, just thru the GEC busbar and the gec tap. I don't really see anything in the code that says it needs to connected "directly" to the grounded conductor. Of you are the AHJ I guess you just have to make the call an whether that is the intent of the code.

PS I am copying this to the regular forum. Please keep the discussion there so others can give their interpretation.

It is connected however size is the problem. Grounded circuit conductor is 500kcmil while the trough is bonded via #2 AWG to ground bus bar which is connected via #4 AWG GEC tap to MBJ #4 AWG to 3/0AWG neutral tap to then 500 kcmil neural. The route would be for each disco as oppose to connection of 500kcmil directly. Would that not be problem? Would it not be easier to do what post #2 says?


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[electrofelon]

It is connected however size is the problem. Grounded circuit conductor is 500kcmil while the trough is bonded via #2 AWG to ground bus bar which is connected via #4 AWG GEC tap to MBJ #4 AWG to 3/0AWG neutral tap to then 500 kcmil neural. The route would be for each disco as oppose to connection of 500kcmil directly. Would that not be problem? Would it not be easier to do what post #2 says?


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As I said, and I have run into this before, the code doesn't say why to do for SSBJ'S where there are multiple service disconnect enclosures. One may be tempted to size a ssbj tap to each disconnect like is prescribed for gec's but again it doesn't say that, so perhaps a full size to each disconnect is required.

As AHJ, you can't say " do #2 it's easier" you would need to point to a code violation in the way they want to do it.

 

[hhsting]

As I said, and I have run into this before, the code doesn't say why to do for SSBJ'S where there are multiple service disconnect enclosures. One may be tempted to size a ssbj tap to each disconnect like is prescribed for gec's but again it doesn't say that, so perhaps a full size to each disconnect is required.

As AHJ, you can't say " do #2 it's easier" you would need to point to a code violation in the way they want to do it.

I guess question is can grounding electrode conductor tap be used as SSBJ and if yes then what size

Also I don’t exactly follow above what you are saying. SSBJ size from service disco to bus bar based on incoming conductors of 3/0awg is #4 but then if you look at incoming service conductor size 500 kcmil it would be 1/0 AWG. 250.80 says grounded system conductor be connected to metal enclosures however if indirectly does not say what size conductors in between. It’s confusing. Your saying #4 AWG tap GEC should be 1/0AWG each service disconnect or should be something different?

 

[hhsting]

As I said, and I have run into this before, the code doesn't say why to do for SSBJ'S where there are multiple service disconnect enclosures. One may be tempted to size a ssbj tap to each disconnect like is prescribed for gec's but again it doesn't say that, so perhaps a full size to each disconnect is required.

As AHJ, you can't say " do #2 it's easier" you would need to point to a code violation in the way they want to do it.

Edit to previous post:

First I guess question is can grounding electrode conductor tap be used as SSBJ and if yes then what size

Second bonding jumper from gnd bus bar to trough is sized #2 AWG should it not be sized #1-0 AWG based on incoming 500 kcmil or based on 2 sets of 3/0 coming from each disco to gnd bus bar? Or at gnd bus bar inside trough their is no incoming ungrounded conductor or equivalent area for parallel conductors so their should not be bonding jumper from gnd bus bar to trough?

Third Also I don’t exactly follow above what you are saying. SSBJ size from service disco to bus bar based on incoming conductors of 3/0awg is #4 but then if you look at incoming service conductor size 500 kcmil it would be 1/0 AWG. 250.80 says grounded system conductor be connected to metal enclosures however if indirectly does not say what size conductors in between. It’s confusing. Your saying #4 AWG tap GEC should be 1/0AWG each service disconnect or should be something different?


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[electrofelon]

Edit to above post:

First I guess question is can grounding electrode conductor tap be used as SSBJ and if yes then what size

Correct. I don't see anything saying I can't. And size, right that is the question can it be sized off the conductors serving that individual enclosure (like gec taps can) or does it need to be full sized. Unfortunately code doesn't give much details on SSBJ'S.

Second bonding jumper from gnd bus bar to trough is sized #2 AWG should it not be sized #1-0 AWG based on incoming 500 kcmil or based on 2 sets of 3/0 coming from each disco to gnd bus bar? Or at gnd bus bar inside trough their is no incoming ungrounded conductor or equivalent area for parallel conductors so their should not be bonding jumper from gnd bus bar to trough?

Third Also I don’t exactly follow above what you are saying. SSBJ size from service disco to bus bar based on incoming conductors of 3/0awg is #4 but then if you look at incoming service conductor size 500 kcmil it would be 1/0 AWG. 250.80 says grounded system conductor be connected to metal enclosures however if indirectly does not say what size conductors in between. It’s confusing. Your saying #4 AWG tap GEC should be 1/0AWG each service disconnect or should be something different?


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[hhsting]

Correct. I don't see anything saying I can't. And size, right that is the question can it be sized off the conductors serving that individual enclosure (like gec taps can) or does it need to be full sized. Unfortunately code doesn't give much details on SSBJ'S.

Let’s concentrate on SSBJ gnd bus inside trough to trough enclosure size: Table 250.122(C)(1) says size SSBJ off of ungrounded conductor or equivalent parallel area. Look at the ground bus bar inside trough has incoming #4 AWG GEC tap, and out going GECs they are all grounded. Their is no ungrounded conductor or equivalent parallel at the gnd bus bar so how can their be #2 AWG SSBJ from ground bus bar to trough?


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[electrofelon]

Let’s concentrate on SSBJ gnd bus inside trough to trough enclosure size: Table 250.122(C)(1) says size SSBJ off of ungrounded conductor or equivalent parallel area. Look at the ground bus bar inside trough has incoming #4 AWG GEC tap, and out going GECs they are all grounded. Their is no ungrounded conductor or equivalent parallel at the gnd bus bar so how can their be #2 AWG SSBJ from ground bus bar to trough?


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It would be sized based on the ungrounded service conductors which are 500. The SSBJ is for the trough which has the 500s in it. Not sure what you mean by "Their is no ungrounded conductor or equivalent parallel at the gnd bus bar".

 

[hhsting]

It would be sized based on the ungrounded service conductors which are 500. The SSBJ is for the trough which has the 500s in it. Not sure what you mean by "Their is no ungrounded conductor or equivalent parallel at the gnd bus bar".

Well the conductor attached to gnd bus bar are all grounded.

How about then GEC tap which salon act like SSBJ size based on incoming service 500 kcmil or incoming to service disco 3/0AWG?

 

[electrofelon]

How about then GEC tap which salon act like SSBJ size based on incoming service 500 kcmil or incoming to service disco 3/0AWG?

As I have said multiple times, there does not seem to be any guidance in the code for parallel SSBJ's to multiple service disconnects. Last time I ran across this I looped a full sized SSBJ from 1st disco, to CT can lay in lug and back to 2nd disco just to be safe. Have fun at the salon