ECN Forum Forums General Topics of the Trade General Discussion Area bonding the neutral

roger, the diagram to the left looks fine. but, if you were to add a bond. jumper to the neutral bar in the right hand diagram. this would be a clearer picture of what im being told to do.

Roger while I agree that with a plastic raceway and eliminating the EGC between the transformer and the first OCPD there will be no direct parallel path between the transformer and the panel.

But I still think and I may be wrong that you would have a path for for neutral current through the grounding electrode system.

If we bond at the transformer and the panel we can eliminate the EGC between them.

We still will have to bring a EGC in with the primary's to provide a fault path back to that system.

Considering that EGC will be connected to the buildings grounding electrode system, along with the transformers GEC I see a potential for current flow on these conductors.

Bob, the grounded conductor is all that is needed for the fault clearing path from the "Main" back to the "Source"

This would be the same for a "Service", just put a meter between the Transformer and the Service Disconnect and install the GEC at the meter or the panel.



Roger

Still having a problem with this.

I will stick with what I am familiar with.

480 delta primary 208 Wye secondary.

There is no grounded conductor on the primary side, we will need the EGC brought to this transformer on the primary side so we can open the 480 breaker, not relying on the building steel connection to do so.

This would be the same as having to bring the grounded conductor to a service disconnect even if we do not intend to use it for loads in the building.

Bob, looking at a residential service for simplicity.

In essence what you are saying is that you feel it necessary to install a Grounded Condutor and an Equipment Grounding Conductor from a pad mounted residential transformer and the Main Disconnect?


Maybe I'm misunderstanding what's being said.

Roger

We could just be misunderstanding each other.

Sticking with the 480 delta primary 208/120 Wye secondary transformer.

If the primary windings fault to the case what is the fault clearing path back to the 480 supply?

A house service includes a grounded conductor, the delta 480 supply has no grounded conductor.

If you do not provide a primary side EGC the only path back to the 480 supply neutral will be through the transformer GEC and most likely building steel back to the service main bonding jumper.

It also could be that I am misunderstanding the function of the bonding jumper at the transformer.

I have to go to bed now, I will talk to you later.

Bob

Bob, me too, good night Bob.

Roger

roger and bob, thank you for the insight into this problem.

just one more question roger, what would the diagram look like if the raceway were changed to steel? would you run a ground wire and use bonding bushings or a bonding bushing with a jumper on one end of the pipe

[This message has been edited by rizer (edited 03-21-2004).]

[This message has been edited by rizer (edited 03-21-2004).]

Roger,

In your diagram of March 19 7:03 PM on the left, I believe that you create exactly the parallel path that Rizer is asking about.

Not shown in the diagram is the ground connection between the disconnect enclosure and building steel or the grounding electrode system. The disconnect enclosure is not simply bonded to neutral and then isolated from all other ground contact, and there will certainly be electrical conductivity between the disconnect enclosure and building steel. This means that the neutral-panel bond in the disconnect is either explicitly or implicitly a bond between the neutral and building steel. In the transformer you also bond X0 to building steel. Net result: normal neutral current flow can follow two paths, either along the neutral wire, or through the multiple ground bonds and building steel or grounding electrode system.

If the PVC conduit were replaced with steel conduit, this would be an explicit and clear parallel path, with neutral to enclosure bonds at both ends of a metallic pathway. IMHO this would actually be safer than the PVC conduit case, because you would now have a situation much like the parallel path found when a residence meter pan is bonded to neutral at the same time that the service disconnect enclosure also has a neutral bond. In this case, there is an explicit parallel path, but it can be very carefully bonded. A low resistance parallel path is often not a problem (unless you get inductive heating), but an overall low resistance parallel path with a high resistance (per unit length) joint _is_ a problem. In homes with neutral problems, the neutral current flowing on the water pipes is not much of a problem until a plumber has to cut the pipe

I think that the policy expressed here (bond X0 only, treat all panels as sub-panels) is the most sensible way to go.

-Jon

Hi Jon,

As far as metallic conduits between meter sockets or CT cabinets and service panels, I will never do that any more.

I have learned much from hanging around these forums and I have come to the conclusion that for my own piece of mind I will not deliberately make a path for the unbalanced neutral current other than the Neutral conductor itself. OK the water serice may be another path, but I do not get a choice on that one

I know that there are literally tens of thousands of installations like you describe that are working fine and will continue to do so.

That said I find no compelling reason to continue to make a parallel neutral path, I know I have seen the results of this current eating away lock nuts and enclosures when the connection is not all it should be and I am sure most electricians have seen that too.

I have been and will continue to use PVC or SE between bonded metering enclosures and bonded service enclosures.

Just my opinion and certainly not a code requirement at this time.

Bob

PS Roger is a pretty sharp guy, he is aware of SDS procedures.

[This message has been edited by iwire (edited 03-21-2004).]