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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
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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.
gs5556
1,233 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
155 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.
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