Running an isolated ground

[cppoly]

Isolated ground receptacles go back to an insulated ground bar on a panel, which then has a direct connection to the street side of a water main of a building.

Questions:

If the building does not use the street side of the water main as one of its grounding electrodes, is this connection of an isolated ground allowed?

Is this connection allowed anyway even if the building uses the street side of the water main as a grounding electrode?

 

[raider1]

The Isolated equipment grounding conductor must be connected to the equipment grounding conductor terminal at the service or the bonding point of a separately derived system.

Check out 250.146(D)

Chris

 

[cppoly]

Thanks, can I ask what the purpose of this is if the grounding terminal of the SDS goes to the same grounding electrode anyway?

 

[iwire]

Thanks, can I ask what the purpose of this is if the grounding terminal of the SDS goes to the same grounding electrode anyway?

Not much at all with todays computer equipment.

 

[Volta]

But the building does need to have the system(s) connected to that water main, if it exists.

 

[cppoly]

I meant what is the purpose of having the isolated ground conductor terminate at the separately derived service's grounding terminal as apposed to running the IGC to a distribution panel then directly to a grounding electrode (water pipe). The grounding terminal of a SDS would go back to grounding electrode anyway.

 

[iwire]

I meant what is the purpose of having the isolated ground conductor terminate at the separately derived service's grounding terminal as apposed to running the IGC to a distribution panel then directly to a grounding electrode (water pipe). The grounding terminal of a SDS would go back to grounding electrode anyway.

Because a ground fault on that isolated grounding conductor has to go back to the source which is the SDS.

It also has to run with the circuit conductors so to do as you suggest the ground fault path would literally pass where it has to go to, run all the way to the GES and than back up the same conduit to the SDS.

Why add that much impedance to the fault path?

 

[cppoly]

Because a ground fault on that isolated grounding conductor has to go back to the source which is the SDS.

It also has to run with the circuit conductors so to do as you suggest the ground fault path would literally pass where it has to go to, run all the way to the GES and than back up the same conduit to the SDS.

Why add that much impedance to the fault path?

Good point