Step Down Transformer & GFCI (Japan)

[NSHHS]

Good day from across the pond here in Japan.

Bottom Line: I have an Open Ground on a GFCI outlet coming from a step down transformer. (See Image).

Question: To correct this I would need an SBj and GEC at the transformer bonding the neutral and ground?

INFO: Applying U.S. code to Japanese construction at a U.S. military base so yeah, we run into a lot of interesting electrical questions.

Fun Fact & Headache: Half of Japan is 50 Hz and the other is 60 Hz.

Thanks in advance!

 

[winnie]

The unbonded secondary would certainly lead to the 'open ground' indication.

However that is a tiny system, small enough that leaving the secondary ungrounded is likely safer than having a grounded system.

On the third hand, there is no leakage monitoring such as one would see in an operating room ungrounded system.

I would not make any changes without discovering the design intent of this system.

 

[NSHHS]

The unbonded secondary would certainly lead to the 'open ground' indication.

However that is a tiny system, small enough that leaving the secondary ungrounded is likely safer than having a grounded system.

On the third hand, there is no leakage monitoring such as one would see in an operating room ungrounded system.

I would not make any changes without discovering the design intent of this system.

This is our bulk liquid O2 storage tank building outside the hospital. The only thing this is tied to is one single GFCI outlet. This was their design instead of running a 120v circuit from our main hospital. They only ran a 200v line for main equipment and stepped down for this single outlet. Thank you. I told my guys to leave it alone and the GFCI should be fine.

 

[winnie]

'Their design' meaning the O2 supply company or the hospital?

In any case I think it is worth questioning whomever supplied the system as to why they did it that way and to confirm that it is exactly as intended.

Keep in mind that the GFCI is essentially _useless_ in this design. The safety comes from the fact that in a small ungrounded system a person could come in contact with either hot or neutral without getting a shock, just like a 'bird on a wire'. The only way someone could get shocked is if they come in contact with both the hot and the neutral.

If they did come in contact with both the hot and the neutral 'downstream' of the GFCI, then they would look like any other load to the GFCI, and the GFCI would not trip. The only time the GFCI would provide any protection is if there were a fault upstream of the GFCI and a person came in contact with the faulted wire and a wire downstream of the GFCI.

Maybe the designer will say 'the ungrounded system is needed for reason xxxx. the GFCI is essentially window dressing because some code requires it, but it doesn't really do anything.' Or the designer will say 'There is this particular failure mode where the GFCI is actually helpful because. Or the designer will say that was supposed to be bonded and we need to go back and check other systems that we built. Or the designer will say 'whoops....'

-Jonathan