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Grounding Metal Outlet Boxes and Isolated Ground Receptacles

Just installed six really nice separate dedicated 20 amp lines (with 6 awg) for my new dedicated listening room.  Decided to use heavy metal outlet boxes so that I could make my six Furutech Receptacles as strong and sturdy as possible.  I also had my electrician run 4-wire 6 agw to the boxes so that we could have one ground wire to the metal receptacle box and then a separate ground wire to the isolated ground screw on the Furutech.

I sent some photos of the setup to a friend of mine (who just happens to be an electrical engineer) and he raised an the issue that since my Furutech Receptacles are metal and they will be screwed into the metal box with metal screws, then we have effectively now tied the two separate grounds together!  Help!  Is that a bad idea?   Is having the box and receptacle setup in this way going to cause issues once my gear is in place; ground loop hums, etc?






stickman451
stickman451 OP
553 posts
 
Thinking that the Furutech GTX-D G was an isoloated receptacle, we decided to use four-wire Romex.  So, one ground wire went directly to the outlet, one to the metal outlet box.  The metal boxes are larger and made it easier to jump from 6 awg down to a short piece of 10 awg that would all fit in the one box.  And the metal boxes are stronger and make it easier to tightly secure the outlet to the box.  

The first question is whether or not the Furutech outlets are actually 'isolated' ground.  I am re-checking that now.  Second question is does it really matter if the outlets are isolated ground or not?  In either case, we have two grounds in the same box, one on the outlet and one tied directly to the metal box.  There are six of these dedicated 20 Amp lines in the room.  Two boxes are for the mono block amps, two are for subs, and the remaining two are for the front-end components.  A two ought line runs from the subpanel to the main panel for the house.  

Since the outlet is metal and the box is metal, we have effectively tied the grounds togther right at the box.  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).  


jea48
4,562 posts
 

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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stickman451 OP
553 posts
 
Yes, both ground wires from the outlet/metal bic are attached to the ground bar in the sub panel.  

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 
jea48
4,562 posts
 
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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stickman451 OP
553 posts
 
The average length of the six dedicated runs is approx 30 feet.  The room is 29' L x 21'-10" W.  The longest two runs are about 36 ft from the front wall back to the sub panel in the room.  The shortest run is about 25' from the sub panel.  

The sub panel is a GE PowerMark Gold.

All of the six 6awg dedicated lines will be on the same phase in the sub panel.  Lighting and standard wall outlets will be on the opposite phase. 

The sub panel in my room is approx 60 ft from the main panel (which is in the car garage).  

Not sure on your other questions but should get those answers tomorrow when i speak with the electrician.

The Furutech outlets are Not Isolated Ground for sure.  I checked the continuity with a Radio Shack tester and the ground screw is connected to the outlets metal mounting brackets.

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!

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