GEC

[A/A Fuel GTX]

In trying to understand the science of grounding, am I correct in saying that the main reason for the GEC is to enhance the grounded conductors reference to earth?

 

[bphgravity]

Re: GEC

No. That statement means nothing. Section 250.4(A)(1) describes the reason the NEC requires grounding of electrical systems. These are all questionable at best.

 

[pierre]

Re: GEC

"That statement means nothing."

I agree it may not be the most important part, but... means nothing?

 

[iwire]

Re: GEC

Originally posted by pierre:
"That statement means nothing."

I agree it may not be the most important part, but... means nothing?

A grounding electrode can not make a neutral the same potential as the earth if there is a real electrical connection forcing the neutral to be of higher potential than the earth.

Imagine a service that the utility neutral has opened.

Is there any amount of grounding electrodes that will hold the neutral at zero potential to earth?

 

[don_resqcapt19]

Re: GEC

A grounding electrode can not make a neutral the same potential as the earth if there is a real electrical connection forcing the neutral to be of higher potential than the earth.
Imagine a service that the utility neutral has opened.

You don't even need an open neutral to have voltage and current on the grounding system. nall utility systems where the primary distribution is a grounded system, there will be a voltage equal to the voltage drop on the primary neutral at the grounding electrode system. There is nothing that you can do to eliminate this voltage. In fact the NEC even requires that we energize our pools with this voltage.
Don

 

[iwire]

Re: GEC

Originally posted by don_resqcapt19:
You don't even need an open neutral to have voltage and current on the grounding system.

Don I agree, I was just trying to provide a clear example.

 

[George Stolz]

Re: GEC

Originally posted by don_resqcapt19:
In fact the NEC even requires that we energize our pools with this voltage.

Can you elaborate? I don't understand.

 

[iwire]

Re: GEC

The required equipotential grid is tied directly to the utility's neutral.

The utility's neutral is not at the same potential as the earth and during fault conditions will have a potential much higher than the earth.

 

[iwire]

Re: GEC

This how I consider grounding electrodes and it is just a creation of my strange mind.

Thinking a grounding electrode will electrically connect an electrical system to earth is akin to thinking a sail is mechanically connected to the wind blowing on it.

Yes the wind will influence the sail but if another stronger force acts against it the wind loses.

Take the above for what its worth, just the odd thoughts of my mind.

 

[George Stolz]

Re: GEC

Originally posted by iwire:
The required equipotential grid is tied directly to the utility's neutral.

I am confused. Can you explain the FPN of 680.26(A)?

 

[George Stolz]

Re: GEC

Originally posted by iwire:
Thinking a grounding electrode will electrically connect an electrical system to earth is akin to thinking a sail is mechanically connected to the wind blowing on it.

Cool analogy.

 

[iwire]

Re: GEC

Originally posted by georgestolz:

Originally posted by iwire:
The required equipotential grid is tied directly to the utility's neutral.

I am confused. Can you explain the FPN of 680.26(A)?

I can give it a shot.

All that FPN reminds us of is that the 8 AWG need not run back to the panel.

I suppose it is remotely possible that the grid remains isolated from the sources EGCs but I think that is very unlikely.

At the pump, a heater, lighting or receptacles the EGCs are very likely to be connected to the same metal objects that the bonding grid is connected to.

For one example

680.26(B)(5) Metal Wiring Methods and Equipment. Metal-sheathed cables and raceways, metal piping, and all fixed metal parts except those separated from the pool by a permanent barrier shall be bonded that are within the following distances of the pool:....

All those parts will be connected to the EGC and the bonding grid.

 

[A/A Fuel GTX]

Re: GEC

OK....So why do we run a GEC, be it a connection to a water pipe, concrete encased electrode, ground ring, ground rod or building steel or all of the above to the grounded conductor to a service? Is it simply for lightning protection?

[ January 16, 2006, 02:21 PM: Message edited by: m73214 ]

 

[iwire]

Re: GEC

Originally posted by m73214:
OK....So why do we run a GEC, be it a connection to a water pipe, concrete encased electrode, groung ring, ground rod or building steel or all of the above to the grounded conductor to a service? Is it simply for lightning protection?

Habit?

IMO, this sums it up

Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines.

 

[don_resqcapt19]

Re: GEC

George,

I am confused. Can you explain the FPN of 680.26(A)?

In view of the wording in 680.26(B)(4) I cannot.

(4) Electrical Equipment ... Where a double-insulated water-pump motor is installed under the provisions of this rule, a solid 8 AWG copper conductor that is of sufficient length to make a bonding connection to a replacement motor shall be extended from the bonding grid to an accessible point in the motor vicinity. Where there is no connection between the swimming pool bonding grid and the equipment grounding system for the premises, this bonding conductor shall be connected to the equipment grounding conductor of the motor circuit

Don

 

[don_resqcapt19]

Re: GEC

OK....So why do we run a GEC, be it a connection to a water pipe, concrete encased electrode, groung ring, ground rod or building steel or all of the above to the grounded conductor to a service? Is it simply for lightning protection?

For the most part that is the reason.
Don

 

[bphgravity]

Re: GEC

This is what I have concluded thus far in my search for the orgins or NEC grounding requirements. Most of the current requirements stem back to old telegraphy theory and application. Grounding in these pre-1900 systems was essential for proper operation and protection against line surges, lightning surges, and ground references.

Edison was a pioneer in telegraphy technology and borrowed from it for his electrical light and power generation and distribution system. Telsa and Westinhouse borrowed it as well in their A/C system. However both camps agreed that a complete insulated system far out performed a grounded system in the prevention of fire. (The problem is providing and maintain a completely insulated system.)

Keep in mind early NEC specifically prohibited the grounding of any conductor of an electrical system. This held up until roughly 1913. But before then, the debate was greater than it is today as to ground or not ground a system. It seems today, that it is just generally accepted as being the best alternative and most pratical method of fire and life safety protection.

Here's an Edison quote:

It is the general opinion of the Edison interest that, while absolute insulation, if it can be had and where it can be had, is preferable, the advantages of grounding the neutral under certain conditions and particularly on large systems, are such as to make that practice in those cases the best working method particularly as a precaution against fire risk.

See, Edison knew that in the lab, conditions could be controlled, however wiring in the field would not and could not be.