GFCI Receptacle with GFCI pigtail

[iwire]

It would be almost impossible to do my job if I was limited to using only NEC terms, after all the NEC is not a "design" manual.

I understand and agree. :smile:

However when we are at an NEC forum it makes a lot of sense to use the NEC terminolgy.

 

[480sparky]

Back to the OPs question:

Plugging in your own 'personal' GFI cord could just be a way that everyone on the job site makes sure the cord they are using is properly GFI protected.

As the various building trades become more and more safety-conscience (either voluntarily or having OSHA show up!), they just may have the attitude of 'use your own GFI cord.... who knows if the job-site receptacle even works right!'

 

[wptski]

GFCI do not sense current on the grounded conductor. They sense a difference between the line and the neutral conductors. They do not care if the stray current is going to ground or if it is going to a different neutral conductor. If the net current in the GFCI is >6mA it is supposed to trip. This is why multi-wire circuits need to have their common neutral connection made upstream of a GFCI.

Look at the diagram that Bob posted. There is no difference in the conductors that are sensed by the two coils. And the sensing portion of the GFCI has no relation to ground.

My explaination was wrong plus way too short. Here's a detailed quote that does it correctly!
>>
To detect a Neutral to Ground fault there is a second transformer (left toroid in the illustration above) placed upstream of the H-G sense transformer (in the illustration above). A small drive signal is injected via the 200 T winding which induces equal voltages on the H and N wires passing through its core.

If N and G are separate downstream (as they should be), no current will be flow in either wire and the GFCI will not trip. (No current will flow in the H wire as a result of this stimulus because the voltage induced on both H and N is equal and cancels.)

If there is a N-G short downstream, a current will flow through the N wire, to the G wire via the short, and back to the N wire via the normal connection at the service panel. Since there will be NO similar current in the H wire, this represents a current unbalance and will trip the GFCI in the same manner as the usual H-G short.
>>

 

[wptski]

I would be surprised if that is so.

It was fairly recently that the standards changed.

Even an 'old style' GFCI without that specific part of the circuit would trip when a load was applied and it had a grounded to grounding conductor fault.

Hmmm, I see your point and that could be true.

 

[juanoito]

Here's the Evidence

Here's the Evidence

This is the GFCI module extracted from a typical temporary supply power box. I'm trying to download a picture. Can't seem to figure it out.

 

[jim dungar]

To detect a Neutral to Ground fault there is a second transformer (left toroid in the illustration above) placed upstream of the H-G sense transformer (in the illustration above). A small drive signal is injected via the 200 T winding which induces equal voltages on the H and N wires passing through its core.

Is this part of the "mis-wired" detection circuitry for GFCI receptacles?

 

[wptski]

Is this part of the "mis-wired" detection circuitry for GFCI receptacles?

I don't think so, it's just what it says, N-G fault. The "mis-wired" detection might be in the chip itself used.

 

[jim dungar]

I don't think so, it's just what it says, N-G fault. The "mis-wired" detection might be in the chip itself used.

I have never seen this extra coil in a GFCI breaker diagram, is it unique to receptacles?

And are you saying that this coil will cause this GFCI to trip if a downstream N-G bond exists even without a load current flowing?

Where did you find an explanation of this coil's function?

 

[wptski]

I have never seen this extra coil in a GFCI breaker diagram, is it unique to receptacles?

And are you saying that this coil will cause this GFCI to trip if a downstream N-G bond exists even without a load current flowing?

Where did you find an explanation of this coil's function?

I'd guess that it's only in receptacle GFCI because I'd think they'd trip because being at the point where N-G are connected together.

Yes, a GFCI just dangling from a cord connected to the line side only will trip when N-G are shorted in the receptacle and when the load connection N-G are shorted.

I did a Google search on "How a GFCI works" and got this page: http://www.codecheck.com/gfci_principal.htm from I quoted the text above but the diagrams don't show up for me! I don't know where "iwire" got his diagram from.

 

[ELA]

I have never seen this extra coil in a GFCI breaker diagram, is it unique to receptacles?

And are you saying that this coil will cause this GFCI to trip if a downstream N-G bond exists even without a load current flowing?

Where did you find an explanation of this coil's function?

Yes wptski is exactly correct.
This was discussed previously in another post. It surprised me at first so I did my own research. I had called Leviton to get information as to what resistance was low enough to be detected and could not get an answer. So I bought one and tested it.

No load current is required and if the resistance from neutral to PE is less than approx. 30 ohms the GFCI will trip.
The second core injects a signal into the load side and if there is a low enough resistance from neutral to PE the GFCI will trip (even through there is no load on the recepticle.

here is a link:
http://www.rhtubs.com/GFCI/GFCI.htm

 

[jim dungar]

I'd guess that it's only in receptacle GFCI because I'd think they'd trip because being at the point where N-G are connected together.

Yes, a GFCI just dangling from a cord connected to the line side only will trip when N-G are shorted in the receptacle and when the load connection N-G are shorted.

I did a Google search on "How a GFCI works" and got this page: http://www.codecheck.com/gfci_principal.htm from I quoted the text above but the diagrams don't show up for me! I don't know where "iwire" got his diagram from.

I have never seen a major GFCI manufacturer that says or even infers that they will trip on a N-G bond without some amount of load current flowing. I know that this is not a standard feature of all GFCI devices and do not believe a "single" website reference.

I have looked at literature from Hubbell, Leviton, Pass & Seymour, Cooper Wiring Devices, and Technology Research Corporation Inc. Hubbell mentions their continuous self-check feature. P&S talks about their open neutral protection. Cooper and TRC describe their automatic reset version. But no one mentions N-G connections.

 

[wptski]

I have never seen a major GFCI manufacturer that says or even infers that they will trip on a N-G bond without some amount of load current flowing. I know that this is not a standard feature of all GFCI devices and do not believe a "single" website reference.

I have looked at literature from Hubbell, Leviton, Pass & Seymour, Cooper Wiring Devices, and Technology Research Corporation Inc. Hubbell mentions their continuous self-check feature. P&S talks about their open neutral protection. Cooper and TRC describe their automatic reset version. But no one mentions N-G connections.

Jim:

And the point is what? It doesn't exsist?

I have a Leviton, Cooper and P&S here. I'm positive about the P&S, it was the barnd connected that I spoke of. A portable unit, known as Shock-Buster also acts the same too. ELA picked up a Leviton to test and it also function as stated too. I could connect the Cooper but I'll bet it'll do the same.

Look at how the manufactures specs are listed for GFCIs. Minimum trip current 4-6ms and maximum trip time of <25ms. I wrongly assumed that was 4-6ma at <25ms!

 

[don_resqcapt19]

Bill,
They will test out the same way, with or without the extra coil if there is current on the neutral on the line side of the GFCI.
Don

 

[wptski]

Bill,
They will test out the same way, with or without the extra coil if there is current on the neutral on the line side of the GFCI.
Don

Don:

With the extra coils, they trip as soon as power is applied.

 

[Energy-Miser]

I haven't run any tests but just from the way ground and neutral wires are connected (at the MB panel), it is clear that in a branch circuit that is not under load at any of its outlets, then both the N and the G will be at the same potential level all the way through the length of that branch circuit. For such a circuit a N-G short should not trip any of the GFCI's on that circuit. However, if the BC is loaded anywhere, then the N will be carrying current (from the point where the load is attached back to the panel), and this current will create a voltage drop on the N, which will put it at a different potential with respect to the G (which under normal circumstances is a non-current-carrying conductor). An N-G short on the branch circuit which is under load, as described, will then casue some of the return current of the N to go through the G in a parallel path (due to the voltage difference described), thus reducing the current the is passing through the N. Any such N-G short downstream from a GFCI will be deteced by the GFCI circuit as an imbalance between the H and the N, and if the imbalance is around 4-6 ma or higher, should cause it to trip, IMO. e/m

 

[wptski]

For such a circuit a N-G short should not trip any of the GFCI's on that circuit. However, if the BC is loaded anywhere, then the N will be carrying current (from the point where the load is attached back to the panel), and this current will create a voltage drop on the N, which will put it at a different potential with respect to the G (which under normal circumstances is a non-current-carrying conductor). An N-G short on the branch circuit which is under load, as described, will then casue some of the return current of the N to go through the G in a parallel path (due to the voltage difference described), thus reducing the current the is passing through the N. Any such N-G short downstream from a GFCI will be deteced by the GFCI circuit as an imbalance between the H and the N, and if the imbalance is around 4-6 ma or higher, should cause it to trip, IMO. e/m

Look at the diagram and read the text, the extra coil injects a small signal into lines, so it can calculate a N-G short without a load. ELA and myself have tested this. Pickup a GFCI, rig up power to it and try it yourself.

 

[jim dungar]

And the point is what? It doesn't exsist?

I don't believe I have said that no GFCI has this feature, but I apologize if I did. What I have tried to say is, N-G testing is not a typical feature nor a requirement for UL listing. If this not part of the UL standard it should not be included in a description that implies all GFCIs have it.

It is a fact that not all GFCIs perform N-G testing.
It is a fact that receptacle style GFCIs have additional requirements than circuit breaker style (i.e. they must check for mis-wiring between line and load)
It is also a fact that portable GFCIs have additional requirements than standard receptacle style units (i.e. they must check for an open line side neutral).

 

[Energy-Miser]

Look at the diagram and read the text, the extra coil injects a small signal into lines, so it can calculate a N-G short without a load. ELA and myself have tested this. Pickup a GFCI, rig up power to it and try it yourself.

Yes, thanks I looked and according to the article and the diagrams, such a secondary coil will allow the GFCI to trip on a N-G short, even in absence of load. Without the secondary coil (apparently they don't all have that), I stand by my explanation above, as for these GFCI's there will be no way for them to know that a N-G short has occured if there is no load on the BC. e/m.

 

[wptski]

I don't believe I have said that no GFCI has this feature, but I apologize if I did. What I have tried to say is, N-G testing is not a typical feature nor a requirement for UL listing. If this not part of the UL standard it should not be included in a description that implies all GFCIs have it.

It is a fact that not all GFCIs perform N-G testing.
It is a fact that receptacle style GFCIs have additional requirements than circuit breaker style (i.e. they must check for mis-wiring between line and load)
It is also a fact that portable GFCIs have additional requirements than standard receptacle style units (i.e. they must check for an open line side neutral).

Jim:

Just to double check, my Leviton, P&S and Cooper all work the same way, maybe not required but they do!

 

[wptski]

I stand by my explanation above, as for these GFCI's there will be no way for them to know that a N-G short has occured if there is no load on the BC. e/m.

That was already mentioned prior to your post.