Service Ground questions?

Clutchcargo · 05-03-2007, 03:16 PM

I need to move the main ground to make room for a cleaner running raceway. This means I need a new ground wire because it will need to be a few inches longer.
1. What gauge wire do I need for 100A service?
2. Can the ground share the conduit with other circuits or does it need to be by itself?
TIA

jwhite · 05-03-2007, 07:19 PM

What are you calling the main ground? What is a cleaner running raceway?

Why would you put the ground wire in this raceway?

Is this in your home, or a business?

Clutchcargo · 05-03-2007, 07:41 PM

This is for my home.
The ground from the service panel runs diagonally across the basement ceiling in 1/2" emt and connects to the main water lines. I would rather route this instead to follow the perimeter of the basement. I was thinking if I can also share the conduit with 14G Thhn, this would work perfectly for adding a few additional recepticals in the basement.
The raceway is a separate item, this would be for the second floor power. I only brought this up because the ground is in the way. This is just going to be 5 or 6 branch circuits (romex) tacked to a 1x4. It would look much cleaner if I can make it a straight shot from the panel to where it will enter the wall.
Thanks

jwhite · 05-03-2007, 08:15 PM

The wire from the panel to the water main, is the main grounding electrode conductor. If it is run in metal conduit, it should have a fitting on the end near the water pipe that electrically connects the copper wire to the metal conduit.

Its purpose is to send to ground any overcurrent from a lightning strike.

I do not know of any code restriction about using this same raceway for other circuits, but I know a bit about inductance, and believe that objectionable currents could be induced in any circuit that was in the same conduit as the GEC.

I reccomend you run a new raceway for the new circuits.

Clutchcargo · 05-03-2007, 08:33 PM

Thanks,
What do you mean "objectionable currents"?

jwhite · 05-03-2007, 08:55 PM

If two wires are near eachother, a high voltage/current in one, will induce a voltage/current in the other.

The magnitude of the induction is a complex formula, but the result is that "objectionable currents" can be induced in the other line.

An "objectionable current" is just that. A current that you would normaly object to. For example a DVD player that normaly draws 1 amp, but is forced to take 100 amps due to a fault. The extra 99 amps are objectionable.

So if you run the circut to your DVD in the same condut as your main ground, and a T-storm hits, then you risk the objectionable currents flowing through your DVD.

Clutchcargo · 05-03-2007, 09:18 PM

Thanks, great explanation.

jwhite · 05-03-2007, 09:37 PM

All the above said, there is not guarntee that all of the fault current from the storm will go to the ground. But it is the best we can do.

that is the reason for the Grounding Electrode, and the Grounding Electrode Conductor.