Neutral Backfeed

[Volta]

into the xformer i have a-b-c with a ground and no neutral. from the xformer i have a-b-c-n with a ground. x0 is not bonded to the ground, but the subpanel is grounded with its own grounding conductor. from what i know x0 is not required to be bonded? do any of you believe that could be the cause...because the secondary neutral is not bonded? what gets me is that other circuits from the SAME secondary panel do not have this problem. just these 8 circuits feeding this little upfit. my thinking was that its something to do with the circuits being multi-wire circuits, but ive never had that problem before, and like i said those breakers were off, and the ungroundeds did not have voltage.

Think of the transformer as its two main components:
1. The metal non-current carrying enclosure, and
2. The windings.

The first you took care of by the feeding EGC. Ok.
The second though is a new electrical system, and the neutral (X0) is to be connected to ground through a GEC to the Grounding Electrode System (GES).

the subpanel is a main breaker panel, i suppose i could install the bonding jumper in that panel and all will be solved then?

Yes, if the GEC is also run to that point. See 250.30(A).

 

[notoriousdln]

as it is. thanks alot guys!

 

[iwire]

Here is an example drawn by Ed, a member that used to be provide a lot of help here.

 

[cadpoint]

Bob, thanks for posting that drawing, (Ed, thanks for taking the time to draw it),

I frankly keep forgetting which wire get's sent uncut to the body of the trannie! :roll:

 

[kwired]

Here is an example drawn by Ed, a member that used to be provide a lot of help here.

Nothing against Ed, but he needed to provide the second option of bonding in the first disconnect in his drawing as well as show a panelboard that contains one to six main breakers, then he would have covered the topic fairly thoroughly.

 

[iwire]

Nothing against Ed, but he needed to provide the second option of bonding in the first disconnect in his drawing as well as show a panelboard that contains one to six main breakers, then he would have covered the topic fairly thoroughly.

Take my word for it, Ed had drawings for each subject, he was an electrical instructor and along with being very knowledgeable was a heck of a nice guy.

http://forums.mikeholt.com/search.php?searchid=3173948

 

[Rockyd]

Seen it before when Neutral and ground ARE NOT BONDED AT XO then all kinds of ghost voltage presents itself.

Recommend that the OP consider going here -

​

Buy it.

Click on the pic.

 

[Rockyd]

250.30(A)(1) is site specific. The first OCPD is acceptable, but always believed it was better to tie at XO. XO point seems to be industry standard, even though both methods are acceptable (one, or the other, but not both!).

 

[iwire]

250.30(A)(1) is site specific. The first OCPD is acceptable, but always believed it was better to tie at XO. XO point seems to be industry standard, even though both methods are acceptable (one, or the other, but not both!).

Sometimes both, not my method but allowed with non metallic conduit.

 

[Rockyd]

Forgot about plastic, good heads up Bob

 

[Smart $]

250.30(A)(1) is site specific. The first OCPD is acceptable, but always believed it was better to tie at XO. XO point seems to be industry standard, even though both methods are acceptable (one, or the other, but not both!).

Sometimes both, not my method but allowed with non metallic conduit.

Forgot about plastic, good heads up Bob

But that is only in cases where there is no EGC/EBJ run in the pipe... and just how do you have no EGC/EBJ?

With an EGC/EBJ run in the pipe, you can only bond at one point... otherwise you'd be creating a parallel path for grounded conductor current.

 

[kwired]

But that is only in cases where there is no EGC/EBJ run in the pipe... and just how do you have no EGC/EBJ?

With an EGC/EBJ run in the pipe, you can only bond at one point... otherwise you'd be creating a parallel path for grounded conductor current.

you would not need one in this case - no different than what you would have between a meter socket and service disconnect if running non metallic raceway.

I would want the transformer to be mounted on something non conductive also otherwise an unintentional bond could be created and then you would have neutral current flowing through objectionable paths.

 

[Smart $]

you would not need one in this case - no different than what you would have between a meter socket and service disconnect if running non metallic raceway.

...

I understand that is how many look at it, and I would not have any problem with it being installed that way.

However, how do you get around the requirement of 250.110 for the enclosure to be connected to an EGC. Many will say the requirement is met with the primary EGC. I say the transformer is a part of two systems and therefore needs an EGC from each. JMO.

I believe the 2011 NEC will eliminate the no grounding conductor possibility, as it will likely require a supply-side bonding jumper (SSBJ).

 

[Smart $]

...

I would want the transformer to be mounted on something non conductive also otherwise an unintentional bond could be created and then you would have neutral current flowing through objectionable paths.

If the transformer is in or about the same structure as a service-supplied system, it may utilize a common grounding electrode with the service. Thus a neutral current path is created through the primary and secondary GES' and the primary EGC.

 

[iwire]

Many will say the requirement is met with the primary EGC. I say the transformer is a part of two systems and therefore needs an EGC from each. JMO.

IMO there is no such thing as a secondary side EGC until you pass the first over current device.

 

[don_resqcapt19]

...Many will say the requirement is met with the primary EGC. I say the transformer is a part of two systems and therefore needs an EGC from each. JMO. ...

I agree that the primary EGC cannot be used for the secondary equipment grounding. However in the case where XO is bonded at both the transformer and the OCPD enclosure, I see no need for an EGC or a supply side bonding jumper between the two locations.

 

[don_resqcapt19]

you would not need one in this case - no different than what you would have between a meter socket and service disconnect if running non metallic raceway.

I would want the transformer to be mounted on something non conductive also otherwise an unintentional bond could be created and then you would have neutral current flowing through objectionable paths.

How is it that these objectionable paths for grounded conductor current are a big deal on a SDS, but are actually required to be created on a code compliant installation of a service?

 

[kwired]

How is it that these objectionable paths for grounded conductor current are a big deal on a SDS, but are actually required to be created on a code compliant installation of a service?

I have wondered that myself. If I can I like to use non metallic raceway between meter and service disconnect for this reason.

 

[Smart $]

... However in the case where XO is bonded at both the transformer and the OCPD enclosure, I see no need for an EGC or a supply side bonding jumper between the two locations.

I agree, provided a path has not been created for neutral current other than the grounded conductor. To create such a path by equipment grounding with the grounded conductor would be a violation of 250.6(A), 250.30(A)(1), and 250.142.

While the possibility of a compliant installation exists, the commonplace installation of transformers under NEC purview are within a service-supplied building or structure, and are typically connected as an SDS. The required grounding electrode is likely to be electrically common with the service system GES, and thus create a path for objectionable current.

 

[iwire]

The required grounding electrode is likely to be electrically common with the service system GES, and thus create a path for objectionable current.

It can't be objectionable, it is sometimes required.