Grounding Metal Outlet Boxes and Isolated Ground Receptacles

Yes, both ground wires from the outlet/metal box are attached to the ground bar in the sub panel.

Glad to hear that. That’s the way it should be done.

You would be surprised how many posted messages I have read over the years on audio forums where the IG safety equipment grounding conductor was connected directly to the earth connection (Grounding Electrode) for the main electrical service. Or the IG ground was connected to an isolated earth driven ground rod that is not tied, bonded, to the main grounding system of the electrical service, which is quite dangerous. Neither of the two methods meet NEC code.

The purpose of the equipment grounding conductor is to provide a low resistive path for ground fault current to return to the source, the electrical service grounded neutral conductor.

The 2 ought from the sub panel runs back to the main panel. The main panel is grounded to the steel rebar in the house foundation

Just curious, did the electrician wire the new sub panel 120/240V?

2 hot wires, 1 neutral wire, and 1 equipment ground wire.

Did he use 1/0 - 3 with ground romex?

Metal conduit and install three 1/0 conductors plus an insulated equipment ground conductor?

1/0 - 3 with ground MC (Metal Clad) armor cable?

How far (distance) is the sub panel from the main electrical service panel?

If the sub panel is 120/240V did you tell the electrician to feed all 6 dedicated 120V branch circuits from the same Line, leg, from the panel? All from Line 1 (L1) or all from Line 2 (L2)? Audio equipment that is connected together by wire ICs should be fed from circuit breakers fed from the same hot Line, leg, and neutral.

What manufacture brand electrical panel did he install? Style/model? Copper bus? Example, Square D QO.

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What is the average length of the 6 dedicated 20 amp branch circuits? Longest? Shortest?

How did the electrician terminate, connect, the #6 wire to the 20 amp circuit breakers?

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Are the six 20 amp circuit breakers CAFCI ( Combination Arc Fault Circuit Interrupter) type?

Example: http://www.homedepot.com/p/Square-D-QO-20-Amp-Single-Pole-CAFCI-Circuit-Breaker-QO120CAFIC/202353307...

Or maybe this style, a plug on neutral CAFI breaker/panel system.

http://www.schneider-electric.us/en/product-range/62194-qo-plug-on-neutral-cafi-circuit-breakers/

How did the electrician terminate the #6 neutral wire to the breaker?

IF the sub panel is a Load Center panel it must look pretty busy, full, inside. (A Load Center electrical panel is the type of panel used typically in a residential dwelling unit.)

Or did the electrician install an actual electrical panelboard that is physically much bigger than a Load Center. Lots more wiring space inside. About twice the price of a Load Center.

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Main issue is I do not want to create an electric hazard (pretty sure my electrician is very capable) and I do not want to create a bunch of ground loop issues!

From the description of the wiring materials and wiring methods used in your posts everything meets or exceeds electrical safety code. At least NEC. I would imagine your electrician followed any local electrical codes that differed from NEC.

As for any ground loop problems, just my opinion, your branch circuits runs are too short to cause any ground loops. If they were long, say 60ft to a 100ft, the 6-3 with ground may have been a problem as I described in an earlier post. Especially paralleling the bare equipment ground wire with one of 3 insulated conductors of the cable.

I wouldn’t be surprised though if the electrician doesn’t rework the equipment ground wiring in the six wall rough-in outlet boxes after you tell him the 6 duplex receptacles are not IG grounding type duplex receptacles. He has to hang his name and reputation on the job when he’s done.

As far as the way I would do it now, knowing the duplex receptacles are not IG, I would cap off the insulated wire in the box and just leave it as a spare unused wire. I would pigtail the bare equipment ground with two pigtails. One to bond the metal box and the other to connect to the ground terminal on the duplex receptacle.

(Just going from memory the construction of 6-3 with ground NM-B cable (Romex), the bare ground wire is in the middle of the three twisted insulated wires. For me anyway, that lessens any chance of an induced voltage transfer from the hot and neutral current carrying conductors onto the equipment ground wire.)

As for what to do with the spare capped off wire of the 6-3 with ground Romex at the electrical panel end? Normally it would be capped off and left laying in the bottom of the panel for future....... But in this instance it is part of a cable assembly that will be feeding an audio system. An audio system where the user has spent big bucks in hopes of getting the lowest noise floor possible. I would wonder if the floating insulated wire might act as an antenna and pick up air born RFI. I would probably connect the end at the panel to the ground bar. Nothing wrong with that as far as a code issue. Ask your electrician if he has a problem with it.

It would be nice to hear from Al, (almarg), what he thinks. Would he connect the end of the spare insulated wire at the electrical panel to the ground bar, or leave it floating above ground?

Jim

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One option we are looking at is to pull out the metal boxes, put in a high quality plastic or fiberglass box and elimintate any ground to the box.

I don’t think the electrician will find a plastic or fiber receptacle outlet rough-in box big enough for 6-3 with ground that will meet NEC for the conductor fill requirements. (2014 NEC 314.16) That’s why, I believe, the electrician used a steel square box with a single gang raised device cover. I personally would leave what you have now. If the receptacle supporting back strap was made of steel then you might hear a difference in sound. The supporting back strap on the Furutech is not made of ferrous steel. What type of duplex cover plate are you going to use? THAT can change the sound of your audio system!