Objectionable Current (Art. 250.6)

[benaround]

I think the question here is, Why would opening the primary disconnect to

the transformer eliminate the current flowing on the primary EGC if the cause

is a neutral/ground on the primary system?

It should not matter if tranny is powered up, as the path is solidly connected

back to the source.

 

[harrycan]

Is it just me?

Is it just me?

I think the question here is, Why would opening the primary disconnect to

the transformer eliminate the current flowing on the primary EGC if the cause

is a neutral/ground on the primary system?

It should not matter if tranny is powered up, as the path is solidly connected

back to the source.

YES! That's exactly my point and why I ams very confused about the whole result. In fact I did this three times to make sure I wasn't "seeing" things...

 

[SmithBuilt]

Have you disconnected all the load side conductors including the load side ground and neutral and conduit to be sure its not the transformer?

Basically isolate the transformer housing with the exception of building steel. Just don't touch it.


The Emperor may have poor quality control at his ISO certified manufacturing plant.

 

[winnie]

It should not matter if tranny is powered up, as the path is solidly connected

back to the source.

This point confuses me as well.

I could imagine that somehow the current flow on the primary feeder is somehow magnetically coupling to the EGC. This makes the EGC the secondary of an inadvertent transformer, and then since the EGC is bonded to building steel at both ends, this transformer has a shorted secondary.

This is extremely unlikely if all three feeder conductors are in the same conduit with the EGC, since all three conductors would be similarly coupled to the EGC, and unless there is a fault, the _net_ current on the feeder is zero, and thus the net coupling to the EGC is zero. But if somewhere in the conduit system some of the feeder conductors and the EGC follow different paths, then this current flow might be caused by induction. Basically situations that could induce current flow in conduit systems could induce current flow on the EGC.

You could try lifting the EGC that comes in with the primary feeder, and measuring the voltage between that end and local bonded metal.

-Jon