Dedicated lines: use isolated grounds? Subpanel wiring?

[lem321]

I've perused the forum for information on dedicated lines for my audio system. Some recommend using an isolated ground (IG) in their lines, while others have not. While I'm in the process of putting together a shopping list of parts, I must also choose some audiophile duplex receptacles. Most of the well-known ones mentioned here (e.g. Oyaide, Furutech) do not seem to have a model with an IG facility. Does this make an IG somewhat of a moot point?

Secondly, having my electrician also add a subpanel which will be about 25-30 ft. from the main panel. What do you recommend I use to connect the main to sub panel? 3 gauge is commonly mentioned. Should this be run in an aluminum, steel or other conduit (impractical to run it inside the walls)?

Thanks in advance for any advice you may offer.

[Odyssey]

Read the White Paper at this site:

http://www.ground1.com

[jdandy]

Originally Posted by lem321

I've perused the forum for information on dedicated lines for my audio system. Some recommend using an isolated ground (IG) in their lines, while others have not. While I'm in the process of putting together a shopping list of parts, I must also choose some audiophile duplex receptacles. Most of the well-known ones mentioned here (e.g. Oyaide, Furutech) do not seem to have a model with an IG facility. Does this make an IG somewhat of a moot point?

Secondly, having my electrician also add a subpanel which will be about 25-30 ft. from the main panel. What do you recommend I use to connect the main to sub panel? 3 gauge is commonly mentioned. Should this be run in an aluminum, steel or other conduit (impractical to run it inside the walls)?

Thanks in advance for any advice you may offer.

Wilson.......If your in-wall receptacle junction boxes are plastic, you will still have a dedicated ground back to your subpanel providing each circuit has a separate and unshared ground wire from the receptacle to the panel's ground bar even if the receptacle does not have an isolated ground. With plastic junction boxes and romex cable back to your subpanel from each outlet it will be irrelevant whether the ground at the outlet is separated from the metal mounting strip on the receptacle or not. Isolated ground receptacles only separate the grounded terminal from metal junction boxes that are grounded back to the panel. If your receptacle junction boxes are plastic they will not be grounded. Just be certain that each dedicated receptacle has its own dedicated ground wire back to the subpanel ground bar. In addition, it is wise to ensure all the dedicated circuit runs to your subpanel are of the same length to guard against potential ground differences between outlets that can cause hum in connected audio components.

You did not mention the size of your subpanel but #3 copper with THHN insulation will provide 100 amps. A 100 amp residential subpanel will use three #3 copper wires and a #8 copper ground wire. The circuit breaker supplying current to your subpanel will be the determining factor in wire size needed.

You did not say whether your subpanel will be located inside or outside. This generally determines the type of raceway required. You can feed a 100 amp subpanel with 1-1/4" schedule 40 PVC conduit, EMT conduit, intermediate metal conduit, or rigid metal conduit. Your electrician should be able to advise you based on the route and exposure conditions.

[Mike1998]

If you have a ground that is not any good it can cause all sorts of noise, however, incorrectly installing an isolated ground can also be dangerous:

https://en.m.wikipedia.org/wiki/Isolated_ground

If your ground is noisy you may just want to consider having another installed.

[lem321]

Thanks for all your comments and recommendations guys!

I wanted to respond to some of Dan's (jdandy's) questions:
1) The subpanel will probably be a Square D 100a panel. I plan on having three 20a circuits for now.
2) The (25') feeder will run from the main panel inside an enclosed garage to a subpanel. From there, the 3 branch circuits will go up one floor to the HT/audio room outlets (10-15').
3) Regarding conduits - I presume there is no benefit of one conduit over another from the standpoint of shielding or sound quality. My electrician said rigid metal (EMT) is probably the way to go. Hadn't thought of using PVC.

[jdandy]

Wilson.......Thanks for the response. Installing the subpanel feeder in EMT, which by the way is not rigid metal conduit, will work just fine. Schedule 40 PVC conduit is satisfactory as well. The purpose of metal raceways (EMT, IMC, or RMC) is to protect wire from physical damage, not to provide any type of shielding. A Square D panel would be my choice, too.

[lem321]

Hey Dan,
Thanks a lot for all the great advice. Nice to have a pro on AA!
Wilson

[lem321]

Would you guys twist both the feeder wires and branch circuit wires (10/2) as has been suggested on the Bill Whitlock writings? Is solid core better than stranded for the large feeder wires (#3)?

[Masterlu]

I don't twist; and I use solid wire.

[jdandy]

Wilson.......You will not find #3 insulated copper in solid wire. Stranded wire in that size is the standard. The National Electrical Code requires #8 gauge and larger wire to be stranded when installed in a raceway.

I would not twist the wires going to your dedicated branch circuits. If you are using type NM-B cable (Romex), simply install it flat in the center of your studs. If you are using conduit to your branch circuit outlet boxes you can install stranded or solid #12 wires right off the wire reels. Attempting to twist multiple conductors will created tension on the wires at the points where the wire transitions around bends in the conduit and is not recommended.