Grounding for building expansion

[Jennifer K.]

Hello-I have seen variances of the question I am going to ask on the forum however I still am not clear on direction. For the case of a building expansion where there is a 3-hr rated firewall separation between the existing building and the new, should the new building have a completely separate grounding system from the existing building? Both buildings (due to their size) are fed by multiple exterior pad mounted transformers. These transformers are not utility type, but owned by the building-utility power upstream of exterior medium voltage equipment.

 

[augie47]

250.30(A)(6) would require a common grounding electrode for multiple SDS in each building (Likely building steel). I don't know of any requirement for separate buildings to have a common connection although I would think it would be a good idea to reduced the possibility of any potential.

 

[petersonra]

Hello-I have seen variances of the question I am going to ask on the forum however I still am not clear on direction. For the case of a building expansion where there is a 3-hr rated firewall separation between the existing building and the new, should the new building have a completely separate grounding system from the existing building? Both buildings (due to their size) are fed by multiple exterior pad mounted transformers. These transformers are not utility type, but owned by the building-utility power upstream of exterior medium voltage equipment.

It needs to have a common GES. Beyond that, everything is a design decision.

 

[Jennifer K.]

250.30(A)(6) would require a common grounding electrode for multiple SDS in each building (Likely building steel). I don't know of any requirement for separate buildings to have a common connection although I would think it would be a good idea to reduced the possibility of any potential.

Thanks for your response! My concern with connecting the two building systems (assuming each would have it's own grounding electrodes) is that then there would be a parallel ground path established. It is my understanding connection with earth should only happen at one point in a system.

 

[tom baker]

Thanks for your response! My concern with connecting the two building systems (assuming each would have it's own grounding electrodes) is that then there would be a parallel ground path established. It is my understanding connection with earth should only happen at one point in a system.

You are correct on the parallel paths, but the NEC recognizes that issue, are requires a common GES