GEC to What? - Electrician Talk - Professional Electrical Contractors Forum

Cletis · 04-08-2012, 10:40 PM

Where do you land your GEC from water main to what? of an ungrounded system (say 3 phase delta. no high leg or corner ground) ????

Cletis · 04-08-2012, 10:48 PM

Oh, and the service starts at CT outside then goes into 4 seperate panels all with mains (2-200's and 2-100's). So, main to speak of

BBQ · 04-08-2012, 10:53 PM

Doze ya be haveing a kodes bok%

Cletis · 04-08-2012, 11:03 PM

Quote:

Originally Posted by BBQ

Doze ya be haveing a kodes bok%

yeah. cant find it. Says to first means of disconnect. There is no "First Means" then come out of CT and go to all 4 symetrically. So, can I land it into any disconnect? I'd have to add a terminal bar as well as there isn't one since there are no neutrals or grounds in panel

don_resqcapt19 · 04-09-2012, 07:16 AM

See 250.24(D).

Cletis · 04-09-2012, 09:50 AM

Quote:

Originally Posted by don_resqcapt19

See 250.24(D).

You may not have understood the question?

I think you meant (E) ?

(E) Ungrounded System Grounding Connections. A premises
wiring system that is supplied by an ac service that is
ungrounded shall have, at each service, a grounding electrode
conductor connected to the grounding electrode(s) required by
Part III of this article. The grounding electrode conductor shall
be connected to a metal enclosure of the service conductors at any accessible point from the load end of the service drop or
service lateral to the service disconnecting means.

Therefore, so according to this I need to run the GEC from the CT Metal to the water main ? or to each of the 4 main panels?

Cletis · 04-09-2012, 09:52 AM

I forgot to mention that they ran 4-SER's (and cut off the ground 4th wire) from CT to 4 Mains, therefore, not bonded if that means anything for the GEC landing?

don_resqcapt19 · 04-09-2012, 10:57 AM

Quote:

Originally Posted by Cletis

You may not have understood the question?

I think you meant (E) ?

(E) Ungrounded System Grounding Connections. A premises
wiring system that is supplied by an ac service that is
ungrounded shall have, at each service, a grounding electrode
conductor connected to the grounding electrode(s) required by
Part III of this article. The grounding electrode conductor shall
be connected to a metal enclosure of the service conductors at any accessible point from the load end of the service drop or
service lateral to the service disconnecting means.

Therefore, so according to this I need to run the GEC from the CT Metal to the water main ? or to each of the 4 main panels?

Yes, I did mean (E).

don_resqcapt19 · 04-09-2012, 10:59 AM

Quote:

Originally Posted by Cletis

I forgot to mention that they ran 4-SER's (and cut off the ground 4th wire) from CT to 4 Mains, therefore, not bonded if that means anything for the GEC landing?

Then it has to be bonded to each of the "stand alone" metal parts and to the EGCs for the equipment served.

Cletis · 04-09-2012, 11:21 AM

Quote:

Originally Posted by don_resqcapt19

Then it has to be bonded to each of the "stand alone" metal parts and to the EGCs for the equipment served.

Ok. Almost there. No egc's btw. Now, does the gec conductor need to be continuous from ct to all 4 main panels then to water main???

acrwc10 · 04-09-2012, 12:21 PM

If you have an un-grounded system, are you using ground detectors ?
Keep in mind (and most guys don't get this) if you have an un-grounded system and you have a fault that is "striking" you can actually run the fault voltage up higher then the system voltage, then someone comes along and touches it and gets killed.
I personally don't like un-grounded systems, to much trouble when you could just corner gground it and be done.

Cletis · 04-09-2012, 02:24 PM

Quote:

Originally Posted by acrwc10

If you have an un-grounded system, are you using ground detectors ?
Keep in mind (and most guys don't get this) if you have an un-grounded system and you have a fault that is "striking" you can actually run the fault voltage up higher then the system voltage, then someone comes along and touches it and gets killed.
I personally don't like un-grounded systems, to much trouble when you could just corner gground it and be done.

I didn't see any bulb detectors anywhere. Wasn't really looking anyhow. I was only called because they ran a circuit and the inspector said he wanted the "Service" Grounded. That's all I know

acrwc10 · 04-09-2012, 04:48 PM

Quote:

Originally Posted by Cletis

I didn't see any bulb detectors anywhere. Wasn't really looking anyhow. I was only called because they ran a circuit and the inspector said he wanted the "Service" Grounded. That's all I know

Well I guess you could ask the inspector,"do you want me to ground the system, or just the metal parts of the system?"

It is possible he isn't aware of what he's looking at, (an ungrounded system) or he maybe very aware of what he is looking at and wants it grounded.

BBQ · 04-09-2012, 05:02 PM

Quote:

Originally Posted by acrwc10

Keep in mind (and most guys don't get this) if you have an un-grounded system and you have a fault that is "striking" you can actually run the fault voltage up higher then the system voltage, then someone comes along and touches it and gets killed.

I have to say I am not getting it.

Running the voltage up on what?

And then what are they touching?

How does the voltage exceed the supply voltage?

acrwc10 · 04-09-2012, 05:11 PM

Quote:

Originally Posted by BBQ

I have to say I am not getting it.

Running the voltage up on what?

And then what are they touching?

How does the voltage exceed the supply voltage?

I get this question every time I post that statement. A fault on a non grounded system that "strikes" or is intermitent causes an effect like a capacitor. The voltage can rise well above the system voltage. Read up on ungrounded systems, it sounds impossible but it is a serious hazard. The "touch what" would be any part that is getting energized by a fault.

Cletis · 04-09-2012, 07:01 PM

Here is something I lifted off another site about this subject

Q 1. One use of an ungrounded system is safety. Now that may sound surprising but for anyone working on equipment at mains voltages it is essential. It is a requirement in the UK that electrical repair workshops and people using mains equipment on building sites must have electrical isolation between the mains supply and the user equipment. In the case of building workers the supply needs to be 120v max for safety.

The secondary winding of the isolating transformer is always left 'floating', ie. ungrounded. If the operator then gets connected to one of the poles, no injury will result because there is no path through which current can flow. If one pole had been grounded and the operator touched the other pole, then assuming he was in contact with the ground, he would receive the full voltage across his body with possible fatal results. True, there will be a small capacity between the secondary winding and ground, but this will be minimal and present a high impedance to any current flow.

Q 2. Whether the supply is grounded or not will make no difference to the provision of a steady voltage to the load. That is determined by the source impedance of the supply. The voltage is provided between the wires which deliver the supply, not by any grounding arrangements.

Q 3. Strictly speaking you are right and there is always some degree of capacitive coupling to ground, but it can be so small as to be insignificant.

Consider standing under a high voltage pylon where the wires are at half a megavolt to ground. There is some capacitive coupling between the wires and you, but it is so small you would never feel the effect.

Hope that clarifies things

Cletis · 04-09-2012, 07:10 PM

Here. I found some more fascinating stuff on ungrounded systems

Ungrounded Systems

Ungrounded systems operate without a grounded conductor. In other words, none of the circuit conductors of the electrical system are intentionally grounded to an earth ground such as a metal water pipe, building steel, etc. The same network of equipment grounding conductors is provided for ungrounded systems as for solidly grounded electrical systems. However, equipment grounding conductors (EGCs) are used only to locate phase-to-ground faults and sound some type of alarm.
Therefore, a single sustained line-to-ground fault does not result in an automatic trip of the overcurrent protection device. This is a major benefit if electrical system continuity is required or if it would result in the shutdown of a continuous process. However, if an accidental ground fault occurs and is allowed to flow for a substantial time, overvoltages can develop in the associated phase conductors. Such an overvoltage situation can lead to conductor insulation damage, and while a ground fault remains on one phase of an ungrounded system, personnel contacting one of the other phases and ground are subjected to 1.732 times the voltage they would experience on a solidly neutral grounded system. (See picture below).
Note: All ungrounded systems should be equipped with ground detectors and proper maintenance applied to avoid, as far as practical, the overcurrent of a sustained ground fault on ungrounded systems. If appropriate maintenance is not provided for ungrounded systems, a grounded system should be installed to ensure that ground faults will be cleared and the safety of circuits, equipment, and that personnel safety is ensured.

An ungrounded system does not have a grounded (neutral) conductor routed between the supply transformer and the service equipment because the supply transformer is not earth grounded.

don_resqcapt19 · 04-09-2012, 07:41 PM

Quote:

Originally Posted by BBQ

I have to say I am not getting it.

Running the voltage up on what?

And then what are they touching?

How does the voltage exceed the supply voltage?

There is a bit of information on this here.

acrwc10 · 04-09-2012, 07:42 PM

What type of work is being done that they have an ungrounded system? In general the only type of electrical system that should be ungrounded is one that a GREATER hazard would occur if the system shut down, like a crane or some other process that needs to be completed to be safe.

Cletis · 04-09-2012, 07:58 PM

Quote:

Originally Posted by acrwc10

What type of work is being done that they have an ungrounded system? In general the only type of electrical system that should be ungrounded is one that a GREATER hazard would occur if the system shut down, like a crane or some other process that needs to be completed to be safe.

Old Machine Shop/Assembly line stuff