Fire Alarm system grounding

[ChrisGS]

Hi everbody ,

I was on a job today were the subject of the proper grounding of the fire alarm system came up .

As I understand it , the fire alarm panel is to have it's own Fused cut-out service , fed from the line side of the main disconnect , with a ground wire(run in conduit) of no less than #10 awg hooked-up directly to the street side of the water main .

I was told today , that the ground wire for the fire alarm fused cut-out can be hooked-up to the grounding bar of the main disconnect .

One of the reasons that I'm cofused about this , is that (again , as I understand it) the neutral "bar" of the fused cut-out is to be bonded to the ground at the fused cut-out ...Now , if that bonded fused cut-out is hooked up to the ground at the main disconnect (which is also bonded) doesn't that create a ground loop ?

Can anyone set me right on this subject ?

Thanks ,
Chris.

 

[iwire]

Chris, in any building with multiple service disconect switches 'ground loops' are inevitable.

Doing it either way you describe ends up with a 'ground loop'.

 

[ChrisGS]

Hi Iwire ,

Thanks for getting back to me, but I'm still confused .

I think of as the first way I described it ...I've got two separate "services" each having it's own dedicated ground, and each bonded at their own neutrals ...The grounds are running in parallel , so I don't think that I see a loop .

...The second way I described it ...Even though I have two separate and parallel power feeds , the grounds are running in series...both bonded to their neutrals...I think that I see a loop between the ground and the neutral .

I'm pretty sure that I remember being told that something like that is wrong .

Chris .

 

[iwire]

I've got two separate "services" each having it's own dedicated ground, and each bonded at their own neutrals ...The grounds are running in parallel , so I don't think that I see a loop

Parallel to what? I don't understand.

If you have two or more services in one building each with their own bonding and GECs you have a loop.

From the utility grounded conductor through one panel down that GEC to the electrode continuing on the second GEC back through the second panel back to the utility grounded conductor.

There is no way I know to comply with the NEC and not create ground loops with multiple service disconnects.

You going to have some unbalanced neutral current flowing through the GECs.

For that mater even in a single service situation their is current flowing on the GEC due to multiple bonds on the supply side of the service.