1. Home
  2. tech-talk
  3. 1193373011

Is 10/3 OK instead of 10/2 wire

Hello

My electrician is doing an electrical rough-in for a HT room for me and has gone ahead with the following:

1) Ran 3/3 gauge off the main panel to a 100amp SquareD
'QO' type commercial subpanel.

2) From here he ran 12 dedicated lines to the home theater
room. Problem is he used 10/3 wire instead of 10/2. He
had the wire running through metal gang boxes. The
receptacles are yet to be installed.

I have some questions and confirmations though......

a) With 10/3 wire in this setup I do understand the black wire is hot, white is neutral, and red is either another hot or a ground wire to be tied into the 'isolated ground bar' at the subpanel, I think. The bare copper wire would terminate inside the metal box and ground the box.
We are swapping out the metal boxes and going plastic now which alleviates the need for the bare wire. Do the electricians just cap or tape the ends of the bare copper wires? Still, I'm stuck with this red wire again and am unsure if this is any different than using a 10/2 wire setup if I'm correct in saying it goes back to the subpanel and an 'isolated ground bar'.

b) I do understand that with 10/3 wire I could do an isolated ground circuit with each outlet having its own separate grounding and not tied into the main system's ground. I don't however want to have to buy dedicated IG receptacles when I have 12 cry'oed Hubbell 8300HI type outlets ready for install. These are not isolated ground type receptacles, as would be my situation with the 10/3 wire. I don't think the electrician installed a separate ground rod or tied into a copper pipe.... So I don't know if we can use 10/3 wire with standard hospital grade receptacles or must they be used in an isolated ground type of setup with those type of receptacles.(orange ones with the litte triangle on the front)

c) What are the benefits of 10/3 over 10/2 if any? Is it just that it can be tied back to a panel with its own isolated ground bar....and what advantage does this isolated ground bar hold if, when it is mounted on a subpanel that is connected to a main panel? This question I pose in the absence of a separate grounding rod.

Thanks to all who can offer some insight. Dave.
canucks0
jea48
2,944 posts
 
1) Ran 3/3 gauge off the main panel to a 100amp SquareD
'QO' type commercial subpanel.
3/3 + a ground wire?
=========

2) From here he ran 12 dedicated lines to the home theater
room. Problem is he used 10/3 wire instead of 10/2. He
had the wire running through metal gang boxes. The
receptacles are yet to be installed.

Question:
He ran 12 individual runs of 10-3 w/grd?
===========

Answer to question a)
If you are using plastic boxes there would not be any need for isolated ground, (IG), type recepts. Even if you had used a metal box isolated from the other metal boxes with only one dedicated circuit per box, there would not be any need for IG recepts. IG recepts are usually used when metallic conduit and metallic boxes are used and the customer wants the equipment ground of the recept isolated from the ground of the conduit because of noise.

As for going to the plastic box over the metal many recommend such.

As for the bare ground wire not being used, now, I would probably still terminate it on the ground bar in the sub panel. Floating it could act like an antenna. Bonded at the panel it will just work like a drain wire in the NM-B 10-3 w/grd cable.
===========

b) your recepts are fine, no reason for IG recepts.

I don't think the electrician installed a separate ground rod or tied into a copper pipe....
NEC requires the equipment grounding feeder conductor shall be run in the same raceway, or cable, as the feeder conductors that will feed the sub panel. The equipment grounding conductor must terminate in the same panel the feeder conductors are fed from.

All supplemental grounding electrodes, ground rods, must connect to the main grounding electrode system of your home.
========

c) What are the benefits of 10/3 over 10/2 if any? Is it just that it can be tied back to a panel with its own isolated ground bar....and what advantage does this isolated ground bar hold if, when it is mounted on a sub panel that is connected to a main panel? This question I pose in the absence of a separate grounding rod.

In your instance none. You just paid more money for the 10-3, unless he sold it to you for the same price as 10-2.

You use the term isolated ground bar.... Please be more specific. Is the ground bar isolated from the sub panel enclosure by insulated stand-offs?
gs5556
769 posts
 
The reason he probably used 10/3 is because he had it on his truck. It's common stock; 10/2 is an oddball order. Not a problem.

An isolated ground receptacle is used only when you have metal clad feeders (aka BX or MC) connected to metal boxes. The receptacle's ears are in contact with the box and the box is bonded to the metal clad feeder which forms the ground path. If you want to isolate the receptacle from the metal box, there's a piece of plastic or rubber between the ears of the outlet and the box, isolating the grounding path. That's all there is to an IG outlet. You then have to connect the third wire to the receptacles' grounding screw and the other end to the ground bus of the panel.

In a subpanel, the neutral wires are connected to the neutral bus and the ground wires are connected to the ground bus (only for Romex with metal or plastic boxes or IG circuits). The neutral and ground buses must be isolated from each other. The neutral bus is hooked up to the white #3 wire that goes back to the main panel

Look at the neutral bus. It is mounted on a piece of plastic and next to it is an "S" or "J" shaped hook screwed to the metal panel back. This is the bonding strap. This hook must be removed or not connected to the neutral bus. The ground bus is not sitting on plastic but is bonded to the panel. As it should be. This is critical for the neutrals to run directly to the main house panel. If they were bonded to the subpanel, the current in the neutral wire would energize the panel leading to ground loop hum backfeeding the hot wires. If a loose ground happens to be between the subpanel and the main panel, it could make other receptacles "hot" via the grounding path.

It's a lot, but that's what you're paying the electrican for.
jamnesta
151 posts
 
Audiophile's and there zeal to avoid noise forget about the safety aspect of a ground wire. Your equipment needs the ground (the bare copper wire) so you have a return path to trip the circuit breaker in the event your component has a short between the hot lead and the casework. It's that simple and has nothing to do with the materials used in the boxes or the conduit, neither of which can be counted on to replace a continuous ground wire.
canucks0 OP
44 posts
 
Here's today's developments....

1) 3/3 to Square D QO type subpanel.

2) 12 dedicated runs to all the outlets (plastic gang boxes)

3) To each outlet the black will be hot, the white, neutral and the red returned back to the subpanel and all the red wires put onto an isolated ground bar. This bar will be grounded to the outside and a grounding rod buried deep.

4)Since plastic outlet boxes will be used the bare copper wire in the 10/3 will not be used and tied off.

5)Now I can use normal hospital grade receptacles and not IG type. All because the isolated ground bar (holding the red wires from all the outlets) will have its own ground to outside and separate from the main panel.
Note: The red wire will be green taped and and grounded at the subpanel.

Thanks to all of you guys.
jea48
2,944 posts
 
1) 3/3 to Square D QO type subpanel.
How did the electrician ground the panel enclosure? Is it just floating? NEC, to the best of my knowledge, does not allow a metallic raceway to be used as a feeder equipment ground. Depending on the breaker size, the electrician installed in the main panel to feed the sub panel, will determine the minimum size of the wire. Example, a 60 amp breaker a #10 awg copper wire. 70 through 100 amp breaker, a minimum size #8 awg copper wire. (NEC 2005, Table 250.122)

In your case where you have an isolated ground bar you would have to install two insulated equipment ground conductors. One for the panel enclosure and one for the isolated ground bar. Both ground wires must be ran in the same raceway as the feeder conductors, and terminate in the main panel as the feeders are fed from......
==========

3) To each outlet the black will be hot, the white, neutral and the red returned back to the sub panel and all the red wires put onto an isolated ground bar. This bar will be grounded to the outside and a grounding rod buried deep.

5)Now I can use normal hospital grade receptacles and not IG type. All because the isolated ground bar (holding the red wires from all the outlets) will have its own ground to outside and separate from the main panel.
Note: The red wire will be green taped and and grounded at the subpanel.
Your electrician may not be licensed. Did you ask him if he was? No reputable licensed electrician would install an isolated ground rod that does not tie back to the main panel bonded neutral/ground.

What you will end up is great for hunting fish worms in the event of a ground-fault. Lousy though for a low resistive fault current path back to the source.

NEC 2005 250.4 (A) (5) Effective Ground-Fault Current Path.
(page 70-92)

"The earth shall not be considered as an effective ground-fault current path."
More to discover