GFCI on ungrounded system (system grounding, not equipment grounding)

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MechEdetour

MechEdetour

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A GFCI receptacle will work on a 2 wire circuit (grounded system) without an equipment ground. It senses current imbalances between the hot and neutral, which when present, it will trip. This makes sense to me and there is no less than a thousand articles on this topic. However, my questions is, will a GFCI receptacle work on an ungrounded system?

On a grounded system, to my understanding the leakage would go through the body and into the ground to return to the source, and the resulting imbalance would cause it to trip. Technically there wouldn't be a return path through the ground to the source on an ungrounded system. You would be brought to the same potential, and there wouldn't be shock hazard. Am I right here?

Seems like I answered my question writing this through... To me it seems like GFCIs are useless on ungrounded systems. Actually, can GFCIs even be used on ungrounded systems? There would be no grounded/neutral conductor. Am I going mad?
 
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I've hooked up a world of hot tubs on a two pole gfci w/o a neutral

I'm fairly sure i was sane at the time......:)

~RJ~
 
romex jockey said:
I've hooked up a world of hot tubs on a two pole gfci w/o a neutral

I'm fairly sure i was sane at the time......:)

~RJ~
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RJ, Your source, the PoCo transformer secondary, is solidly connected to Earth. The OP is asking about a source, and the attached wiring system, that is NOT connected to Earth.

It's an interesting question.

I'll take a stab at the theory. With an ungrounded system there is some form of ground fault detection attached to some form of an alarm. The first connection of one leg of the system to ground isn't the one that causes damage. . . the connection of the NEXT system leg is the one that completes a short circuit.

A person normally would not come in contact with the ungrounded system conductors, but, in the case of a piece of equipment supplied from an ungrounded system through a GFCI receptacle (or breaker), if the piece of equipment is faulted in a manner that connects one ungrounded system leg to the person, that is the FIRST connection of the ungrounded system to ground. No current would flow except for what is necessary for the system ground fault detector. THAT current, passing through the person, if in excess of the 5 milliamp threshold, will trip the GFCI receptacle (breaker).
 
MechEdetour said:
Seems like I answered my question writing this through... To me it seems like GFCIs are useless on ungrounded systems. Actually, can GFCIs even be used on ungrounded systems? There would be no grounded/neutral conductor. Am I going mad?
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You wouldn't have any current flow to trip the GFCI on the first fault, so the GFCI wouldn't have any imbalance to cause a trip till after the second fault.

In a perfect world your ungrounded system would have a ground fault indicator which would light up on the first ground fault and the problem would be corrected before the second ground fault.
 
al hildenbrand said:
RJ, Your source, the PoCo transformer secondary, is solidly connected to Earth. The OP is asking about a source, and the attached wiring system, that is NOT connected to Earth.

It's an interesting question.
Click to expand...

Missed that, my bad Al

Ok, my $.02.....a toroidal coil senses an imbalance , it's not dependent on anything other than that

~RJ~
 
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ActionDave said:
You wouldn't have any current flow to trip the GFCI on the first fault, so the GFCI wouldn't have any imbalance to cause a trip till after the second fault.

In a perfect world your ungrounded system would have a ground fault indicator which would light up on the first ground fault and the problem would be corrected before the second ground fault.
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And if user(s) ignores the ground fault indicator on first fault GFCI will still protect him if there is a second fault.

I have a portable generator - 8000 W 120/240 neutral is not bonded to frame - so it is an ungrounded system. It has 14-30 receptacle and two GFCI protected 5-15 receptacles (factory mounted) on the unit.

Fact it is ungrounded reduces shock hazard some, GFCI still would work if there were a second ground fault.
 
electrofelon said:
I think it comes down to whether the capacitive charging current is high enough to trip the gfci when the fault is made yes?
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I wouldn't say it comes down to only that, but yes capacitive charging current can trip a GFCI - even when part of a grounded system.
 
GFCIs are only recognized for use on solidly grounded systems. I would think if one was applied on an ungrounded system you would have a number of unpredictable issues. Also, since most GFCIs are used in systems of less than 150 volts to ground the systems could not be an an ungrounded system anyway.
 
texie said:
GFCIs are only recognized for use on solidly grounded systems. I would think if one was applied on an ungrounded system you would have a number of unpredictable issues. Also, since most GFCIs are used in systems of less than 150 volts to ground the systems could not be an an ungrounded system anyway.
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What about my generator, and probably thousands that are like it?

Connect the 14-30 receptacle on mine to my premises wiring (with proper transfer equip. of course) and now the generator becomes a part of a grounded system - the 5-15 receptacles mounted on it still are usable and do have GFCI protection.
 
fix quote

fix quote

romex jockey said:
Missed that, my bad Al

Ok, my $.02.....a toroidal coil senses an imbalance , it's not dependent on anything other than that

~RJ~
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Exactly, if you have an ungrounded system supplying a receptacle for example, the first ground will cause the GFCI to trip whether or not there is a load connected at the time. This assumes that the grounding connection is of low enough impedance to allow the trip current to flow.
 
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gadfly56 said:
Exactly, if you have an ungrounded system supplying a receptacle for example, the first ground will cause the GFCI to trip whether or not there is a load connected at the time. This assumes that the grounding connection is of low enough impedance to allow the trip current to flow.
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:?

If you have an ungrounded system how do you get any current flow to trip the GFCI until there is a second ground fault? What goes out on one conductor has to come back on the other and there is no other path even with a ground fault for "leakage current" to flow until there is a second ground fault. This is disregarding current due to capacitive coupling - but even current involved in that situation is extremely low and takes a lot of capacitance before it is a problem.
 
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kwired said:
:?

If you have an ungrounded system how do you get any current flow to trip the GFCI until there is a second ground fault? What goes out on one conductor has to come back on the other and there is no other path even with a ground fault for "leakage current" to flow until there is a second ground fault. This is disregarding current due to capacitive coupling - but even current involved in that situation is extremely low and takes a lot of capacitance before it is a problem.
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Are we talking about a system that is completely isolated from ground (floating), even accidental, or a system that could find earth (ground) on the first fault?
 
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gadfly56 said:
Are we talking about a system that is completely isolated from ground (floating), even accidental, or a system that could find earth (ground) on the first fault?
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TTBOMK grounded means it is intentionally connected at one point (often a neutral conductor) to some reference point that is called "ground" for whatever reason (even if that "ground" is just the frame of a generator), and ungrounded means there is no reference point to other objects of any kind (so floating I guess).
 
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romex jockey said:
I've hooked up a world of hot tubs on a two pole gfci w/o a neutral

I'm fairly sure i was sane at the time......:)

~RJ~
Click to expand...

Ok so this actually answers one of my questions. Don't really need to have a neutral per say... two hots of a grounded system will still allow a GFCI to provide protection. That "path to the source" I am pestering about will allow the leakage imbalance to occur.

kwired said:
:?

If you have an ungrounded system how do you get any current flow to trip the GFCI until there is a second ground fault? What goes out on one conductor has to come back on the other and there is no other path even with a ground fault for "leakage current" to flow until there is a second ground fault. This is disregarding current due to capacitive coupling - but even current involved in that situation is extremely low and takes a lot of capacitance before it is a problem.
Click to expand...

I'm still not convinced leakage current will "exist" on an ungrounded system because it will not have a return path (through earth) to the source.

To hopefully add some clarity: If an ungrounded system has no faults - meaning there are no unintentional connections between ungrounded conductors and dead metal parts/equipment - and everything is hunky dory... Will a GFCI function if I have wet hands?

To push it a bit further, in the case where a single ground-fault does exist, and now the system is unintentionally grounded, will a GFCI function as intended?

It almost seems like a GFCI will only function on a grounded system, or an ungrounded system with a single ground-fault present. Amiright?
 
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No system is ever completely isolated from 'ground'. 'Capacitive charging current' has already been mentioned. Even an 'ungrounded' system will have capacitive coupling to ground, and this current can be large enough to cause a significant shock. If you touch a 'hot' conductor then one phase will be grounded through you, and your body will try to carry the capacitive charging current of the other two phases.

Operating Room isolated ground systems are intentionally small (eg. a single room) to minimize capacitive current.

In principal a GFCI could protect from shock in these situations, but as others have mentioned the GFCI might not be 'listed' for such use.

-Jon
 
But this is an interesting bit of electrical theory we've going here.....

It would appear the contention is that gfci's can't work w/o a path for current to travel

So if we've an isolation Xformer (floating in space?) , H&N or H&H going through a toroidal to a load , said load side would need a source to loose current to?


Is that the jist?

~RJ~
 
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