Grounded Conductor Problems

[George Stolz]

Re: Grounded Conductor Problems

Wayne,

How do you install a device in series with the GEC and not risk losing the path to the grounding electrode?

(That's kind of a trick question.

 

[iwire]

Re: Grounded Conductor Problems

My poor suggestion to Stu aside is this issue really a problem?

I believe the product would be available (read required) if the manufactures thought they could convince the need of it to the NFPA.

Find what is cause of neutral failures and address those problems.

 

[hurk27]

Re: Grounded Conductor Problems

Bob I agree.

George a current relay doesn't connect in series with the load or in this case the GE. It has a current coil that the GEC passes through unbroken, kind of like a GFCI works.

 

[stud696981]

Re: Grounded Conductor Problems

Here is something to think about in regards to the beginning of the post. If you installed a GFI main breaker and it would somehow actually work for a lost neutral, would you still really want this? Here is a bigger problem that would result. You get a small ground fault from something and you end up knocking power out to the entire house. Or if you have a metallic underground water line and some current flows on the GEC instead of all on the neutral..........the main again would trip.

 

[al hildenbrand]

Re: Grounded Conductor Problems

I just had another thought.

There will be currents on the service entrance neutral and GEC that will be produced on the PoCo distribution grid. This current will be in addition to the dwelling load unbalance current splitting at the MBJ between the GEC and the SE Neutral.

Setting a fixed trip level, in my opinion, will result in false trips or no trips at all, unless the GEC current stays in a narrow range.

The amount of load running at any one instant will determine the amount of current on the GEC. . .so I don't think there is a way to build a trigger based on the measurement of the amount of current on the GEC alone.

I think the GEC current has to be compared with the SE Neutral current. If the ratio of the two currents (or maybe the sum or the difference) changes abruptly and remains changed, then that change is the indicator of the neutral loss.

 

[al hildenbrand]

Re: Grounded Conductor Problems

No, scratch sum or difference.

It would have to be the change of the ratio.

One current divided by the other.

If that ratio changes and remains changed for a certain amount of time, then the neutral loss protective device should operate.

 

[hurk27]

Re: Grounded Conductor Problems

By Al: There will be currents on the service entrance neutral and GEC that will be produced on the PoCo distribution grid. This current will be in addition to the dwelling load unbalance current splitting at the MBJ between the GEC and the SE Neutral.

I think this is still the basses of why the GFCI or a GFP wont function anyway is if these currents do not originate from the supply conductors and or do not try to return upon the neutral (which by the way is now open and would not have any current flowing) they would be ignored by the trip circuit as they would not be able to produce any current in the current coil. Now if we had a current coil that had just the two hots and neutral with the GEC passing through it in opposite directions, then the loss of the neutral path could cause the trip but would the stray current also trip it?
How about just a current coil on just the neutral that would detect the lack of neutral current the output of this coil in series with a current coil just on the two hots which this coil phased reversed to cancel a no current on neutral coil if no neutral current is being used? But then this would also false trip if they was any stray current on GE?

This would be easy if we had a 4-wire from transformer. Then any voltage difference between the two grounded and grounding conductors would be an indication of a lost neutral and we wouldn't have to worry about the strays.

Ok Charlie E. I'm not going there.

[ July 15, 2005, 10:31 PM: Message edited by: hurk27 ]

 

[jim dungar]

Re: Grounded Conductor Problems

A 2 pole GFI brekaer does not need a neutral connection to protect the circuit. It only need a neutral for the TEST button to work.

I do not know of any 2 pole GFI that looks for any imbalance between conductors. Most devices have a single current sencor that goes around all three conductors. If all of the current that flows out also comes back in, the CT will see a net zero current.

See page 9 of Square D QO breakers.

 

[hurk27]

Re: Grounded Conductor Problems

By Paul: A 2 pole GFI brekaer does not need a neutral connection to protect the circuit. It only need a neutral for the TEST button to work.

It also needs the line side neutral to operate the electronics. Remove the line side neutral and it will not trip when placing a line side neutral to load side hot load on it.

Also by Paul: I do not know of any 2 pole GFI that looks for any imbalance between conductors.

It is because of a current imbalance of the conductors that run through the current sensor or current coil that allows it to work. If there was no imbalance there would be no current developed in the current coil thus no trip.

If all supply current did not return upon the other conductors then the current coil will develop a voltage in it this voltage is what triggers the electronics to trip the breaker.
If all the current does return upon these conductors then they cancel each other out because of being 180? out of phase. Because of this canceling out there is no voltage developed in the current coil.

 

[pierre]

Re: Grounded Conductor Problems

Jim
I tried to paste a copy of the wiring schematic of the 2 pole GFCI breaker, but was unsuccessful.
Take another look at the schematic and you will see that the sensing device (as well as the test button) is connected to the neutral conductor, without the neutral the sensing device will not work.

 

[physis]

Re: Grounded Conductor Problems

Edit: That's the right one

[ July 16, 2005, 06:41 AM: Message edited by: physis ]

 

[iwire]

Re: Grounded Conductor Problems

Sam you still up?

 

[physis]

Re: Grounded Conductor Problems

Yeah Bob. I was going to bed an hour ago 40 minutes ago.

I've been goofin' with this silly shematic since 3:00 and it was only gonna take a few minutes.

Edit: And I changed programs to make the copy and it's all blurry now. Stupid software. :roll:

[ July 16, 2005, 06:49 AM: Message edited by: physis ]

 

[karl riley]

Re: Grounded Conductor Problems

Concerning the current relay coil around the GEC; this is used in UK and other countries and so is a readily available device.

If the POCO neutral is lost, there would be a surge in current on the GEC, and the relay would shut off power. That's how I understand it, anyway.

Karl

 

[don_resqcapt19]

Re: Grounded Conductor Problems

The UK would not have an open neutral problem like we do. The use a 2 wire 240 volt system with one grounded conductor. If the grounded conductor is open, there is no circuit. I don't think that they bond the grounded conductor at the building, but I am not sure.
Don

 

[grandpapastu]

Re: Grounded Conductor Problems

A circuit breaker with integrated test circuitry that continuously monitors the value of voltage L1-N and L2-N would pick up on a distinct change in values if the neutral was lost.
Not? Because GES circuit existing back to source?
O.K. if not, then:
With the test circuitry incorporating a resistive circuit continuously monitoring a test current the test circuit would pick up on a distinct change in the amperage value if the neutral was lost (or loose neutral) because of the higher resistance to source through the main bond jumper and GES.

 

[grandpapastu]

Re: Grounded Conductor Problems

Thank you very much for the technical design answers i need on the two pole GFCI device.

Got to make some calls.
Want to retire.
As to need? We could have used and actually need many hundreds of products long before they were developed and marketed.
EASY for me to concisely detail need for a neutral fault circuit interrupter. I have detailed at least two examples on this forum.

 

[iwire]

Re: Grounded Conductor Problems

Originally posted by grandpapastu:
As to need? We could have used and actually need many hundreds of products long before they were developed and marketed.
EASY for me to concisely detail need for a neutral fault circuit interrupter. I have detailed at least two examples on this forum.

Well I do wish you luck with your endeavor.

Personally I do not see the need for this device.

1)The number of neutrals opening as a percentage of services IMO would be very low.

2)In my opinion it would be better to prevent open neutrals than to require a device to detect them.

As an example if we where to find the most common spot for a neutral to open is at the connection to the utility then it would make sense for the NEC to require a compression connector at that location.

Still having a hard time believing no manufacture has not already looked into such a device.

But admittedly I could be wrong in my opinion and there may be a market for it.

 

[grandpapastu]

Re: Grounded Conductor Problems

I agree with the Stud96981:
I do not want a GFCI on the Main. Not for a residense. No way!
I want a NFCI CB on the main.
Guess I'll just have to do it myself.
Hope I got enough gas.

[ July 16, 2005, 07:15 PM: Message edited by: grandpapastu ]

 

[don_resqcapt19]

Re: Grounded Conductor Problems

Bob,

Personally I do not see the need for this device.

I see about as much need for this device as I see for AFCIs.
Don