Grounding Metal Outlet Boxes and Isolated Ground Receptacles

The first question is whether or not the Furutech outlets are actually ’isolated’ ground.

No, the Furutech GTX-D G is not an Isolated ground type duplex receptacle.

http://www.furutech.com/2013/02/02/1746/

Second question is does it really matter if the outlets are isolated ground or not?

An IG receptacle is used in commercial and industrial buildings where the branch circuit wiring is installed in metallic conduit. The idea, theory, for using an IG is to isolate the equipment ground of the receptacle from the metallic conduit supposedly to prevent electrical noise that may be traveling on the conduit. Believe it or not National Cash Register was the main reason for the use of IG receptacle years ago. Their specs called for an IG receptacle and if they came out and the receptacle for the cash register was not an IG they would not install their equipment until IG receptacles were installed.

In a residential dwelling unit, house, even if the branch circuit wiring is installed in metallic conduit what AC noise could possibly be traveling on the conduit?

When using Romex an IG receptacle would not serve any purpose or added isolation.

As for what you have now I can’t see where it would violate NEC code. Odd yes...

Also I wouldn’t worry about the branch circuit outlet steel boxes. They are fine.

In your last post you mentioned a sub panel..... I assume the electrician terminated both the box ground wire and the receptacle ground wire on the same ground bar in the sub panel. Is that correct? OR do the IG insulated equipment ground wires, that were intended for IG receptacles, pass through the Sub Panel and connect to the equipment ground bar in the main electrical service panel? (Which meets NEC code for an IG receptacle.)

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But, evently all the ground wires end up at the grounding pole ( which by code in our area is the steel rebar in the house foundation).

But, evently all the ground wires end up at the grounding pole

Please explain in detail what you mean......

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Mother Earth does absolutely nothing for the sound quality of an audio system.

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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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