x-frmr & switchgear

[eager2learn]

If you bond the ground to the XO terminal in a transformer - do you also have to bond the groung to nuetral in a switchgear installation

 

[iwire]

I assume the switchgear is on the secondary side of the transformer?

If so in most cases it is a violation to bond at both XO and the switchgear.

 

[eager2learn]

Your assumption is correct - the switchgear is on the secondary side of the transformer - if i bond the ground to neutral there and at the switchgear, then i would have continuity throughout the entire electrical system on site - if for some reason the nuetral got back fed and the swithgear was bonded - there is the potential that the ground could possibly carry this same current - would that be true? please advise

 

[zip1]

Is this a service, or a separately derived system? Is the transformer indoor or outdoor?

 

[SG-1]

If you bond at both locations you will be creating parallel paths for the current to flow through.

 

[eager2learn]

The x-frmr is located outside and it isnt a seperate service - i took the ground coming from the primary side and bonded it to the ground rod located in the x-frmr - i then took a bonding jumper to the XO - one of the journeyman told me they wanted to bond the neutral inside the switchgear to the ground bus - is this overkill and shouldnt the neutral and ground busses be seperate from one aonther in the gear ?

 

[david luchini]

The x-frmr is located outside and it isnt a seperate service - i took the ground coming from the primary side and bonded it to the ground rod located in the x-frmr - i then took a bonding jumper to the XO - one of the journeyman told me they wanted to bond the neutral inside the switchgear to the ground bus - is this overkill and shouldnt the neutral and ground busses be seperate from one aonther in the gear ?

If this was a service, you'd be required to bond the neutral to ground bus in the switchgear (service disconnecting means) AND provide a second neutral to ground electrode connection outside the building (typically at the transformer.)

Since it is not a service, you a required to connect to a grounding electrode which is either a metal water pipe or structural metal grounding, if those electrodes are available (250.30(7)).

You can use a ground rod, only if the water pipe/structural metal grounding methods are not available. So your connection to a ground rod at the transformer may be a violation.

 

[cadpoint]

As a point of reference you could go take a look at some not so light reading on this web page in the low 100's is Ground verses Bonding-12 parts.
Your part is in 3(now I skimmed that quickie) and 4 here, 4 is in reference to 250.30(7) previous mentioned.

You can also use google, images, and just put in any relievent NEC Article number most times it will be either Mike Holt graphics or MH in a ECM mag article.

 

[K2500]

If you bond at both locations you will be creating parallel paths for the current to flow through.

Maybe, maybe not. If not than than see 250.30(A)(1) expt#2
Edit: I did forget about the EGC creating a parallel path, being this is not a service.

You can use a ground rod, only if the water pipe/structural metal grounding methods are not available. So your connection to a ground rod at the transformer may be a violation.

Could you explain this further? 250.54 tells me I can use auxiliary electrodes, also I believe a separate structure requires an electrode in this case. With an outdoor transformer, the pad would be considered a structure, that is if the pad is a separate structure.

I may be off base with the electrode requirement for separate structures, cant find an article that directly covers it.

 

[augie47]

Sometimes my ole brain doesn't perform well.
Let me see if I have this correct.
At Acme Products, POCO installs a pad transformer and drives a ground rod bonding XO in the transformer satisfying their requirements and 250.24(A)(2). They install a CT meter at the transformer. From that point the E/C installs service conductors..phases + grounded (no grounding) and
the grounded conductor is bonded to the service enclosure and available grounding electrodes at Acme Products.

Down the street at Acme Industries the customer has many transformers
and they choose to have POCO meter the primary and the buy or lease their transformers.
They install a new outdoor transformer.
Since their service is the primary, when they install the same arrangement as above, at there transformer do they install the same ground rod ??
Not due to 250.24, but due to 250.30
From their transformer, they would need to install phases + grounded + a grounding conductor which we classify as the system bonding jumper ??
Likewise they bond XO to the driven ground to satisfy 250.30(A)(3).
At the building they would not bond XO to the gear rather bond the
system bonding jumper and then connect the building electrode system.

Is this correct ?

 

[david luchini]

Could you explain this further? 250.54 tells me I can use auxiliary electrodes, also I believe a separate structure requires an electrode in this case. With an outdoor transformer, the pad would be considered a structure, that is if the pad is a separate structure.

I may be off base with the electrode requirement for separate structures, cant find an article that directly covers it.

Look at 250.30(7) for separately derived systems. The grounding electrode SHALL be the nearest one of the following: (1) Metal Water Pipe... (2) Structural Metal...

Only when those electrodes are not available, does Exception 1 allow you to use any of the other electrodes as specified in 250.52(A). 250.54 allows you to use auxiliary electrodes, but these electrodes can't be used to replace the required electrode in 250.30(7). So in the OP, if the metal water pipe or structural metal electrode exist, using a ground rod at the transformer instead of the pipe or structure would be a violation.

Regarding the transformer pad being a structure, I'm not sure that I would read it that way, but I see how you could. But even in that case, the ground rod would be required to be connected to the equipment grounding conductor run with the feeder to the transformer (and to the structure disconnecting means?) per 250.32(B). The grounding of the SDS still must per per 250.30.

 

[eager2learn]

Thank you very much for the knowledge and experience that you guys have - i greatly appreciate your time

 

[ronaldrc]

If its the Main of that system yes if its a sub feed no.