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Inspector_Gadget · Apr 20, 2010, 10:48 AM

How about if there are only 3 wires in a conduit. Can it be used only as 110v and take one of the hot wires, wrap it with green tape and use it as the equipment ground?
An inspector also told me if the panel is in a separate detached building, a ground rod could be used and then you would treat this sub panel as a main and combine the panel grounds and neutrals

donf · Apr 20, 2010, 11:17 AM

You must have misunderstood the inspector.

If you put a sub panel in a detached building and you want 120/240 VAC, then you MUST use a 4 wire feed unless you are only going to use 240 VAC

At the sub panel, you must use at least one ground rod. There must be an Equipment Grounding conductor between the sub panel and the ground rod.

You will connect Black, Red as hot loads. Neutral will connect only to the Neutral bus and must be isolated from the ground bus. DO NOT USE A NEUTRAL BONDING SCREW.

If there are going to six or more breakers in the sub panel you need to either connect a main cut off switch or install a main breaker in the panel.

You also need to put a breaker into the main panel to protect the feeder from the main to the sub panel.

Inspector_Gadget · Apr 20, 2010, 12:56 PM

No, I have researched this now and found that the sub panel does get ground and neutral bonding.
Hers a link: http://forums.mikeholt.com/archive/index.php/t-57182.html
-Steve-

Missouri Bound · Apr 20, 2010, 04:43 PM

The thread you refer to is 7 years old... it's outdated. Donf has told you the correct way to do it, don't try to find other answers which may be wrong, just because you agree with them. The neutral and the ground are bonded only at the main, never at a sub-panel. That's the NEC code, and the inspector is just wrong, or hasn't kept up with the NEC.

KISS · Apr 20, 2010, 05:31 PM

I'm confused here.

There seems to more than 1 question floating around here and some seem to be made up.

While there is a correct way of doing a subpanel in a detached structure. A 4-wire feed and a ground rod with the neutrals and grounds separate.

There WAS a 3-wire wiring scheme that could be GRANDFATHERED. A ground rod should be used in a detached structure.

Originally Posted by op

How about if there are only 3 wires in a conduit. Can it be used only as 110v and take one of the hot wires, wrap it with green tape and use it as the equipment ground?

Word here, would be 3 insulated wires that you could tape red, white and green and you could use it as a 120 V feed.

Inspector_Gadget · Apr 20, 2010, 08:02 PM

The ground rod has nothing to do with the grounding (bonding) of the two panels. It only provides protection from high voltage spikes such as lightning and contact with high voltage power lines.
With the neutral and ground separated and no ground wire back to the main panel, your ground (bare) wires have no connection with the main and are essentially floating in the subpanel.
If you have no other metallic paths between the garage and main house, and you are still under the 2005 NEC, you may bond the neutral and ground bars (and the enclosure) and make this a compliant installation.

Inspector_Gadget · Apr 20, 2010, 08:14 PM

"Inspector_Gadget;2322656]The ground rod has nothing to do with the grounding (bonding) of the two panels. It only provides protection from high voltage spikes such as lightning and contact with high voltage power lines.
With the neutral and ground separated and no ground wire back to the main panel, your ground (bare) wires have no connection with the main and are essentially floating in the subpanel.
If you have no other metallic paths between the garage and main house, and you are still under the 2005 NEC, you may bond the neutral and ground bars (and the enclosure) and make this a compliant installation."

donf · Apr 21, 2010, 05:56 AM

I give up! Why bother to ask a question when you are bound and determined to do the project your way?

Have at it. Don't let it worry you that you are creating an unsafe condition.

Inspector_Gadget · Apr 21, 2010, 08:39 AM

I see, the Building Inspector I spoke with is wrong, the Electricians I researched are wrong, and yet you, not an Electrician are right.
Hmmmmm.

Inspector_Gadget · Apr 21, 2010, 09:36 AM

Ok, I have spoken to the "Guru" and you are correct, do not bond the Neutral and Grounds in the Sub Panel. He said it is not bad if you do, but it would send a lightning strike through the Neutral bar and circuits in the building, which would not be good.
My apologies for being so hard headed, but until I get proof positive I am not easily swayed.
-Steve-

donf · Apr 21, 2010, 09:49 AM

You are correct! I might also add the Missouri Bound is a licensed Electrician.

Humor me a moment, please. We are talking about a non attached building on your residential property, correct? And that property is here in the U.S.A. correct?

You are planning a main panel feeder, that is protected by a breaker in the main panel to a sub panel with more then six breakers, correct?

You are not talking about a single branch circuit to the non attached building.

The exposure to doing it your way is that you will create a current loop (Neutral/Ground) between the two panels.

If the Neutral and Ground are isolated at the sub panel, there is only one path that the return circuit path can be followed and that is through the grounded conductor (Neutral).

See NEC 2008, 250.32 for information on properly grounding an unattached building.

Inspector_Gadget · Apr 21, 2010, 09:58 AM

No, this is a situation I found in a home inspection I did, and found no ground back to the main panel. I knew that either a ground rod or 2 was needed or a ground back to the Main Panel. The sub panel was not grounded at all, and the ground clamp to neutral bond was not connected.
-Steve-

donf · Apr 21, 2010, 12:01 PM

Okay, I'm sorry that I was so far off base. That was not what I understood you were asking about.

1) At the main service panel, there has to be a grounding system set up. There are several ways to do this:

(A) One or two ground rods connected together and at least 6' apart. An EGC, from the ground rods to the ground bus on the main service panel.

(B) Bond the EGC to the cold water inlet pipe (Metal Only) and the pipe must extend at least 10' beyond the residence and be underground.

(C) "Ufer" grounded copper conductor embedded in a concrete sleeve.

(D) Concrete embedded "Re bar" in the concrete foundation.

Neutral and Ground must be bonded together at the main Panel.

At the non attached building, there must be the grounding methods for the sub panel.

However, you are required by 2008 code to provide a 4 wire feeder. Neutral and ground cannot be bonded together on any sub-panel.

KISS · Apr 21, 2010, 04:03 PM

The whole point of this is to have one and only one reference.
The ground rod thing basically serves two purposes: 1) creates an eqipotential with the earth and 2) Safely discharges lightning strikes.

If you suffer a lightning strike, you don't want the induced currents to raise the potential of the reference that all of the other circuits use.

Two references create ground loops. The current in the ground can change the references of two devices that are communicating. This is a major headache with data aqusition. Generally you avoid the problem with good design.

Cable TV uses ground as a reference and you don't wan't to disrupt that from 0V.

It is possible for the earth to vary it's potential over the length of a large building during a thunderstorm. I know of a computing center that lost most of it's switches due to a storm, not a strike. They had to change the cross computer room connections to fiber.