Neutral Connection in a System Grounding

[jim dungar]

A GFCI only works if it's connected to a supply with a grounded conductor. By grounded, I mean whatever surface one might be in contact with when the accidental touch occurs. In a non-grounded supply, there's no electrocution hazard for the same reason the first ground fault doesn't trip a breaker.

A GFCI works by comparing the current flowing into the line side of the device to the current returning to the load side - what goes out must come back-no more no less. Have you ever had to troubleshoot any GFCI device connected to a shared neutral conductor even though there is no fault to a non-circuit conductor?

Yes, there is no danger of shock if you are truly isolated from the reference plane, but in this case the GFCI does not operate because there is no current flow, the presence or absence of a ground rod has nothing to do with it.

 

[ronaldrc]

Jim

I believe your just giving us a hard time.

The GFI wouldn't work on your wooden kitchen floor if your shoes and floors
are dry.

The neutral and ungrounded conductors go through a CT. coil and null if
they are the same but if current goes around the CT. and its over whats the GFI.
requires which I think is over around 4 milliamps it will kick it out.

It requires a resistance of I think somewhere less that 3000 ohms to accomplish this current.

 

[LarryFine]

A GFCI works by comparing the current flowing into the line side of the device to the current returning to the load side - what goes out must come back-no more no less.

Of course. What I'm talking about is the continuity of the outside-the-loop pathway.

Have you ever had to troubleshoot any GFCI device connected to a shared neutral conductor even though there is no fault to a non-circuit conductor?

Yep.

Yes, there is no danger of shock if you are truly isolated from the reference plane, but in this case the GFCI does not operate because there is no current flow, the presence or absence of a ground rod has nothing to do with it.

I don't disagree. Of course, an isolated body will not get zapped. That's not my point.

If you take a non-grounded supply, and a contact is made by someone who is effectively grounded, the person will not get zapped.

Now, if you add an electrode to that otherwise-non-grounded supply, the person will get zapped.

Likewise, a GFCI device will not operate in the first case, but will in the second.

 

[jim dungar]

The GFI wouldn't work on your wooden kitchen floor if your shoes and floors are dry.

You are correct I do not have a complete circuit, therefore the presence or absence of a building ground rod has nothing to do with my safety. If I touch a faulted toaster and the kitchen sink (which is bonded to the service panel), the ground rod still has nothing to do with my safety. The only time the ground rod affects me is when it is part of the circuit.

The NEC requires us to bond our facilities to ground connections. But zero sequence ground fault protective systems (i.e. GFCIs) will operate properly even if the ground rod is not part of the fault path.

To reiterate, for 600V systems, we are protected from shock by bonding not by grounding to earth. If dirt is going to be part of a possible fault path then it needs to be bonded just like any other conductive surface (i.e. the deck of a ship or the frame of an airplane).

 

[ronaldrc]

Jim

The system has to be grounded before the GFI recpt. will work properly.
I know you know more about Electrical things more than most on here .


If you are serious please down load a brochure on GFIs and study it.

 

[George Stolz]

Connecting to earth is not for clearing the fault. Connecting to earth is to reduce electric shock by reducing the potential of the energized metal piece to ground potential.

Bobby, you're a fairly recent addition to the forum, welcome.

Let's take your gut feeling to the extreme for the purposes of illustration:

Drive a ground rod, and energize a metal pole. In your mind, not physically.

This pole is grounded (connected to the earth).
It's currently in a fault - the housing is energized.
The man is dead.

Why?

Because the connection to earth is not good enough to bring the voltage down on the faulted piece of metal. The man is still dead.

The connection of the rod to the soil is not good enough to raise the voltage of the soil to match the pole. The man is still dead.

The only hope for the man is to get that circuit shut off before anyone has a chance to touch the pole. The only way to get that done is to bond the pole to the EGC, which is connected to the neutral at the service. The bonding connection (N-G) creates an intentional circuit path to overload the breaker and shut down the circuit.

Why do we bother to earth the service, if the transformer is the main focus of our intentional circuiting, and guarding against ground faults?

To protect the equipment and the structure from arcing in the event of lightning or unintentional contact with high voltage lines.

This is the truth these guys have been trying to get across to you. If you think any of these truths is wrong, you need to stop and make sure your pride isn't standing in the way of your learning, it happens to us all from time to time.

Hope that helps,

 

[don_resqcapt19]

Jim

The system has to be grounded before the GFI recpt. will work properly.
I know you know more about Electrical things more than most on here . ...

I don't agree. A GFCI will work just fine on an ungrounded system. It will trip if there is an unbalance in the current between the two conductors. Now the real question is if you can get the 5mA of unbalance that is required to trip the GFCI and if you can't can you get enough current flow to create a serious shock hazard.

 

[George Stolz]

I don't agree. A GFCI will work just fine on an ungrounded system. It will trip if there is an unbalance in the current between the two conductors.

Agreed - but stepping outside of theory, this isn't actually ever done, is it?

Now the real question is if you can get the 5mA of unbalance that is required to trip the GFCI and if you can't can you get enough current flow to create a serious shock hazard.

Bingo - Less than 5mA flowing shouldn't be a serious shock hazard, which is why they're set at that.

(Which I know you know, just saying it out loud. )

 

[brian john]

Bingo - Less than 5mA flowing shouldn't be a serious shock hazard, which is why they're set at that.

Thats what I thought when I installed my 1st GFCI way back in the 70's. So I grabbed the energized condiuctor and it ROCKED my ROLL.

 

[ronaldrc]

I don't agree. A GFCI will work just fine on an ungrounded system. You are saying yes it will It will trip if there is an unbalance in the current between the two conductors. Now the real question is if you can get the 5mA of unbalance that is required to trip the GFCI and if you can't can you get enough current flow to create a serious shock hazard.You just said maybe it want

Well now I've heard it all , I've heard of a trick question but I've never been given a trick answer untill tonight.

Well it want you want be 5 ma. under normal conditions.

 

[jim dungar]

The system has to be grounded before the GFI recpt. will work properly.

There needs to be a complete circuit for current to flow, when there is >5mA of current difference on the conductors the GFCI will trip. Please show me a diagram of how my example of a faulted toaster and a bonded sink requires a ground rod to have the GFCI recept be functional.

Bonding provides paths for current to flow on, ground rods do not. The NEC requires us to BOND together all surfaces, including ground/dirt, that are probable (likely) to carry current.

 

[LarryFine]

I don't agree. A GFCI will work just fine on an ungrounded system. It will trip if there is an unbalance in the current between the two conductors.

With an ungrounded system, the current would have no reason to flow through the body in order to create such an imbalance.

 

[George Stolz]

There needs to be a complete circuit for current to flow, when there is >5mA of current difference on the conductors the GFCI will trip. Please show me a diagram of how my example of a faulted toaster and a bonded sink requires a ground rod to have the GFCI recept be functional.

I think everybody's having a green grass/blue sky argument here.

Jim, I think everybody else is focused on the ground rod at the transformer, not necessarily the local one at the service. Does that make sense?

 

[LarryFine]

Please show me a diagram of how my example of a faulted toaster and a bonded sink requires a ground rod to have the GFCI recept be functional.

In such a case, it wouldn't require an electrode. The bonded sink is taking the place of the earth. If that sink was not bonded, it would be the same thing as an ungrounded system, or an environment with no bonded surfaces.

But, where would you ever have a bonded sink with an ungrounded system? I've been speaking about GFCI's in use where the earth or concrete floor is the grounded surface, because there is a rod, whether local or at the source.

Bonding provides paths for current to flow on, ground rods do not. The NEC requires us to BOND together all surfaces, including ground/dirt, that are probable (likely) to carry current.

Dirt is included in that list because it's a likely 'ground plane reference' when electricity is used outdoors. A GFCI works on a system when grounded by design or by accident. Lose the earth, and the GFCI doesn't work.

The grounded system is why we need GFCI devices in the first place. Without it, the GFCI is ineffective and unnecessary. GFCI's do not detect a hot-to-neutral contact, only a hot-to-grounded-surface contact.

 

[jim dungar]

I think everybody's having a green grass/blue sky argument here.

Jim, I think everybody else is focused on the ground rod at the transformer, not necessarily the local one at the service. Does that make sense?

A ground rod serves no purpose to the proper functioning of a <=600V system. Shock potential is reduced by bonding surfaces together (i.e. by using an EGC) not by connecting them to ground/dirt at the utility pole, at the service entrance, or at any other point.

However because most of our electrical systems are in contact (although it may be indirectly) with ground/dirt, the NEC feels an insured bonding connection (called a GEC) is required. Now that all possible conductive surfaces are bonded together into one large "safety" plane, we can discuss referencing our power system to the plane (with what the NEC confusingly calls a grounded conductor) or letting it float (what the NEC confusingly calls an ungrounded system). Each option has its own circuit protection advantages and disadvantage which relate to faults to the bonded "safety" plane in general. not to any one specific component of that plane.

 

[benaround]

Bobby,

I would like to explain a simular condition, ok.

Let's take a 12vdc auto battery and install the pos. and neg. conductors in a

metal pipe. Where the pipe begins let's drive a ground rod and connect it to

the pipe. At the far end of the pipe 'fault' the pos. conductor to the pipe. The

pipe is now at 12vdc pos. and will stay that way until it gets fixed or if by

chance the neg. conductor also 'faults' and trips the OCPD.

1. Has the 12vdc load remained on, ( pre neg. fault to pipe ) , Yes.

2.What part has the ground rod played in reducing a hazard or reducing the
voltage in this system ?

This ungrounded system is no different than the ungrounded system in this thread.

 

[tryinghard]

I don't agree. A GFCI will work just fine on an ungrounded system...

Don, there really is no such thing as an ungrounded system that includes a neutral. If there is a neutral involved the bonding jumper must be installed and if its not its in violation and extremely dangerous rather than an ?ungrounded system?. Erroneous system would be a better description.

 

[tryinghard]

The system type is determined at it?s origin, it?s grounded if one of the transformers includes a midpoint connection ?XO? with a required bonding jumper (250.20) and it?s ungrounded if none of the transformers include a midpoint connection ?XO? and a bonding jumper, yet the grounding connection is still required to non current-carrying items 250.4(B).

 

[jim dungar]

...it?s ungrounded if none of the transformers include a midpoint connection ?XO? ....

What about a corner grounded delta? How about a transformer with only a 2-wire output?

But, as you mentioned it is the bonding that is most important.

 

[ronaldrc]

If you want to use an analogy

Do this, take a pickup truck set you a 5 kw 120 volt portable generator in the back of it take a extension cord cut the female plug off and splice a temporary light socket pig tail with a 100 watt light bulb in the socket.


Now drive a ground rod in the ground at the back of the truck, Oh say a few feet from the truck.


Now plug the cord in the GFI receptacle that most the new generators have, start the generator the bulb should be lite.

Now take the wire nut off the black wire of the pigtail, but please don't take it apart and get between it.

With the wire nut off and the bulb lite touch the black wire to the ground rod, Please make sure you are not touching the pickup or generator when you do this.

If the GFI trips you all are right if it doesn't Larry and myself are right, I will take your word for it.