ground wire gauge question

[Pete Pasqualini]

I'm running a detached 100A subpanel to a new shop. I have #1 aluminum to run for feed and neutral. What gauge bare wire should I run for the ground? Thanks

[Mark Bolton]

You should be running a four conductor to the sub panel and floating the neutral. The sub panel should have grounds and neutrals isolated. The other option is to drive ground rods at the sub panel location but this is less common. You dont run a bare ground to the sub.

[Jim Neeley]

The other option is to drive ground rods at the sub panel location but this is less common.

Check your local codes as this is not approved in many locations.

[Brad Sperr]

It sounds like you might be running individual conductors in conduit to your shop. You would size your ground wire according to NEC Table 250.122, which is based on the overcurrent protection of the circuit. Assuming that you have between a 60amp and 100amp breaker protecting the feed to your shop, you could use #8 copper or #6 aluminum.

[Pete Pasqualini]

Thank you Brad, that is exactly what I am doing. I'm not sure why the others were "assuming" that I was doing it wrong?? I know how to do it, just didn't know the gauge of wire for ground. Thanks again

[Mark Bolton]

I didnt necessarily assume you were doing it wrong but you said "bare wire".

[Pete Pasqualini]

Yeah, I was visualizing the same wire for the ground rods and wrote bare. Thanks..

[Matt Marsh]

You should be running a four conductor to the sub panel and floating the neutral. The sub panel should have grounds and neutrals isolated. The other option is to drive ground rods at the sub panel location but this is less common. You dont run a bare ground to the sub.

Actually, if this is indeed a seperate detached building, a grounding electrode system must be installed in addition to the equipment grounding conductor ran with the feeder conductors. 250.32(A) All seperate structures that are supplied with power must have a grounding electrode system installed (rods or some other approved type). The only exception is a building that is supplied with a single branch circuit.

If a single rod type electrode is used, the NEC requires an earth resistance of 25 ohms or less. If that cannot be achieved, then a second rod must be driven a minimum of 6 feet away from the first. Rather than screw around with the resistance measurement, it is customary to just go ahead and install the second rod. The 25 ohm max. measurement is then no longer required. #6 is the largest size copper grounding elecrode conductor that the NEC requires to be run to rod type electrodes, no matter the feeder size. A conductor smaller than #6 ran exposed must be protected from physical damage, so #6 is most often used.

Grounding, and Grounding Electrode Systems can be very confusing, as there are often times several factors to consider. For example, if the building utilizes a metal underground waterpipe that is in contact with the Earth for more than 10 feet, it must be used as the primary Grounding Electrode, and be supplemented with another approved electrode(s). Additionally, any and all metal concrete reinforcement, metal building framing members, metal piping systems, etc. must be bonded to this system.

[Matt Marsh]

Also regarding the use of bare conductors for the EGC, NEC 250.118 lists the acceptable equipment grounding conductors.

250.118 Types of Equipment Grounding Conductors.
The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:
(1) A copper, aluminum, or copper-clad aluminum conductor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
(2) through (14) lists the different raceways that are approved to be used as EGCs.

This of course doesn't mean that a particular type of conductor is the best suited for your particular application. If you're using a raceway, stranded, insulated conductors will most often be easiest to install.