Grounding main xfmr and switchgear to same electrode system

[greenspark1]

Hi,
A question came up that the local AHJ doesn't want the main building transformer and the 4W 480V switchgear it feeds grounded to the same grounding electrode system (ground ring plus several ground rods). Both pieces of gear are located about 15' apart so can easily run to the same grounding electrode system. To be clear, they have separate grounding electrode conductors, just share the electrode system. I can't exactly follow his rationale so wanted to see if others have run into this.

While it is not conventional to connect the two grounds together, I don't see any issues that would be caused by this. There is a safe path for any fault current from any downstream equipment back to the source/transformer.

 

[petersonra]

Hi,
A question came up that the local AHJ doesn't want the main building transformer and the 4W 480V switchgear it feeds grounded to the same grounding electrode system (ground ring plus several ground rods). Both pieces of gear are located about 15' apart so can easily run to the same grounding electrode system. To be clear, they have separate grounding electrode conductors, just share the electrode system. I can't exactly follow his rationale so wanted to see if others have run into this.

While it is not conventional to connect the two grounds together, I don't see any issues that would be caused by this. There is a safe path for any fault current from any downstream equipment back to the source/transformer.

The grounding electrode is not supposed to be part of the fault clearing path. If that is what you are doing I can see why he is objecting.

As far as sharing the GES goes, they can even share the GE conductor if it is sized according to the rules for a shared GEC.

I do not understand what you mean by "it is not conventional to connect the two grounds together". It is actually a requirement that all grounding electrodes be bonded together.

 

[greenspark1]

Thanks Bob, sorry for the confusion. I meant that typically the xfmr and switchgear are physically far enough apart that their respective GECs don't run to the same point/system. Yes they are certainly bonded together per Code.

I don't see any reason the two pieces of gear can't share the GES. Am I missing something.

 

[charlie b]

I don't see any reason the two pieces of gear can't share the GES. Am I missing something.

There is only one grounding electrode system. When you bond all electrodes together, they form a single system. Everything that needs to connect to planet earth will necessarily share this same system. It is not you who is missing something, it is the local AHJ who is missing something.