Service Grounding

[crazy_engineer]

I currently have a 600 Amp service 1 phase 240V. I've used a fused 600A safety switch as a service disconnect feeding 2-400A panelboards. I ran a ground with feeder conductors to the pole mounted transformer. Where do I bond the neutral and the ground ?????????

 

[Cavie]

At the 600 amp fused safty switch. The 400 amps panelboards are sub panels

 

[Pierre C Belarge]

What size fuses did you use in the 600 amp rated safety switch?

 

[George Stolz]

Let's keep our terms straight, so we're on the same page.

Look at this picture. Ignore the math crud, I've since forgotten what that was all about. Look at the big letters.

A = Service Conductors
B = Service Disconnect
C = Feeders / Branch Circuits

I ran a ground with feeder conductors to the pole mounted transformer.

I'm going to step out on a limb and make an assumption: I think what you might have meant to say is "I ran an Equipment Grounding Conductor with the service conductors from the pole-mounted transformer."

If this is the case, I understand your confusion about where to bond the neutral and ground - you should not have spec'd an EGC in the service conductors.

Is this the case?

 

[infinity]

I agree with George, no EGC is needed between the transformer and the service disconnect. By installing one you have created a parallel path for the neutral current.

 

[winnie]

While it is arguably a safer system, I don't believe that the NEC has any provisions for services that have separate grounded and equipment grounding conductors. You are _required_ to bond ground and neutral somewhere at or between the service drop and the main disconnect. But if you have a _separate_ grounded conductor and EGC, you would not want this bond, because it would create a parallel path in the EGC, and the bond at the transformer would provide the required path for ground fault current.

If the transformer is customer owned (and therefore a 'separately derived system' rather than a 'service'), then the bond is permitted anywhere between the transformer and the first disconnect.

If the circuit with separate grounded conductor and EGC were run from one customer building to another, and therefore an outside feeder rather than a service, the separate grounded conductor and EGC would be permitted without bonding.

-Jon

 

[bphgravity]

There is nothing in the NEC that prohibits the paralleling of normal operating (neutral) currents on the line side of the service disconnecting means, other than strict enforcement of 250.6...