Delta / Wye vs. GFCI

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mslowley

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Marion, NY
I'm looking for clarification on the following.
Our facilty checked GFCI's this past month and discovered several circuits failed the test. All of them originate in the same 208Y/120 VAC panel supplied by a 480 Delta - 208Y/120 transformer nearby. Upon inspection I see no bond between the neutral and ground bars. This concerns me because the test was conducted using a handheld device (Greenlee) for the purpose, those same circuits are GFCI breakers in that panel and the test button on each of them trips the circuit 100% of the time. If GFCI's work by comparing current out vs. in, why does the breaker test button trip and not when there is a load test conducted? Once we bonded the X0 to Ground, no more problems.
 
Re: Delta / Wye vs. GFCI

The internal circuitry of a GFCI (breaker and receptacle types) use a load resistor, connected in series with the "test" button and between the ungrounded and grounded conductors, to cause a current imbalance to trip the relay.

The plug in circuit testers perform the same test but instead shunt the trip current to the grounding conductor. If you don't have a grounding path, the plug-in analyzers will not trip the GFCI, but that does not mean the GFCI is inoperative. The best way to test them is to do what you did, use the "test" button.

It sounds like you had a more serious problem, an open grounding path. :eek:
 
Re: Delta / Wye vs. GFCI

Are you suggesting that the ground is not solid? If so, at which point? Bus-trans, trans-pnl, pnl-recpt? We did nothing but tie the neutral and ground together inside the panel and it now works. I was thinking that the current was somehow being masked by the other phases at the center tap of the Y in the transformer.
 
Re: Delta / Wye vs. GFCI

If there was no neutral to grounding connection on the secondary of the transformer, there was no fault clearing path, and the plug in GFCI testers would not trip the GFCI.
Don
 
Re: Delta / Wye vs. GFCI

Originally posted by don_resqcapt19:
If there was no neutral to grounding connection on the secondary of the transformer, there was no fault clearing path, and the plug in GFCI testers would not trip the GFCI.
Don
Click to expand...
and this is a good thing since it made you go look further and find the real problem. just pushing the test button on the receptacle itself proves only that the gfci itself works.

the seperate tester also proves the ground is at least conencted.
 
Re: Delta / Wye vs. GFCI

I believe the GFCI should have tripped without the ground. because there should have been enough current to ground to provide the unbalance. GFCI receptacles can be installed on non-grounded circuits and still operate.
 
Re: Delta / Wye vs. GFCI

for reference NEC 210-7(d)(b)and(c) in1999 code. Only book I had in front of me.
 
Re: Delta / Wye vs. GFCI

Laidman,

I believe the GFCI should have tripped without the ground.
Click to expand...
That is true only if we are talking about the test button on a gfci receptacle or breaker.

because there should have been enough current to ground to provide the unbalance.
Click to expand...
A plug in tester will not work properly with a broken ground path.

If the grounding path is broken, there is no complete circuit for the leakage current to take, and the GFCI will not trip.
 
Re: Delta / Wye vs. GFCI

for reference NEC 210-7(d)(3)(b)and(c) in1999 code. Only book I had in front of me.
 
Re: Delta / Wye vs. GFCI

Originally posted by laidman:
That may be true for the tester, but the GFCI will function properly.
Click to expand...
No one is arguing against that, the concern here is the open grounding path.

The original poster made a distinction between using a GFCI tester and the test button.
 
Re: Delta / Wye vs. GFCI

I'll have to go back to this now since you are all making me think that the "gound" is what is missing. I beleive that the ground is carried through from the HV bus all the way to the receptacle. I will repost when I confirm the state of the original ground.
 
Re: Delta / Wye vs. GFCI

I beleive that the ground is carried through from the HV bus all the way to the receptacle.
Click to expand...
The secondary of a transformer is a new system and that is why the code calls it a Separately Derived System (SDS). The grounding on the primary side has nothing to do with the secondary side. You must create a fault clearing path by bonding the secondary grounding conductors to the XO.
Don
 
Re: Delta / Wye vs. GFCI

laidman,
I believe the GFCI should have tripped without the ground. because there should have been enough current to ground to provide the unbalance.
Click to expand...
Where is the path for this current if XO is not bonded?
Don
 
Re: Delta / Wye vs. GFCI

The path for fault current is to earth or any ground even if it is not bonded. there will always be some current. If it is enough it will trip a GFCI
 
Re: Delta / Wye vs. GFCI

Originally posted by laidman:
The path for fault current is to earth or any ground even if it is not bonded. there will always be some current. If it is enough it will trip a GFCI
Click to expand...
How can you pass current through earth with out being referenced to earth?
 
Re: Delta / Wye vs. GFCI

Originally posted by laidman:
The path for fault current is to earth or any ground even if it is not bonded.
Click to expand...
No, the path for all current is back to its source. Without a bond between XO and ground, the grounding conductors are simply floating in space doing nothing - an incomplete circuit.

As Don said, the N-G bond needs to be reestablished on the secondary side of the transformer or else the low impedance fault clearing path is lost.

there will always be some current. If it is enough it will trip a GFCI
Click to expand...
If the small amount of current that is shunted to ground (created by the plug-in tester) has nowhere to go, in this case, an unconnected grouding conductor, then the GFCI will not operate by the tester. Current cannot move without a complete path!

Yes, the GFCI will still operate if a ground fault occurs and a complete path is made back to the source some other way.

[ January 06, 2005, 02:04 PM: Message edited by: peter d ]
 
Re: Delta / Wye vs. GFCI

If that were the case and there could be no fault current why can you install a GFCI on an ungrounded system and have it operate properly and trip.
 
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