ECN Forum Forums General Topics of the Trade General Discussion Area Wiring a Basement Recording Studio

Thanks guys . . . this is exactly the dialogue I was looking for.

Couple of questions:

"If you're particularly concerned about keeping induced hum to a minimum, then maybe go with a metallic conduit installation so that the conduit will act as an electrostatic shield." From Pauluk

But wouldn't this increase the liklihood of capacitive reactance (coupling high freq. currents on the conduit w/ the IG conductor)?

I was talking to an authority in this area today (whose not an electrician, but understands electricity very well) who suggested that I run the insulated ground back to the service entrance grounding point in it's own conduit . . . separate from the hot and neutral. Now I've read that "for safety reasons," you can't run an IG equipment-grounding conductor in it's own conduit.

But why would that be unsafe assuming it follows an effective fault current path?

He also suggested that I use a heavier gauge wire for the ground to lower the impedance thereby reducing the possibility of parallel resonances.

Any thoughts?

Oh and one more thing you guys should enjoy!

He said that running a 220V outlet would be "balanced" by definition. But he admitted that he wasn't sure how one could get their gear hooked up to it. I know my computer is switchable to 220V, but I can't imagine how many codes I would be breaking by doing that.

One more . . .

Is there an advantage (as far as getting cleaner neutrals and grounds)to running branch circuits (for the sensative loads)from a 40 amp subpanel (w/o a transformer in between) over running them from the mains box? Is that one in the same?

OK . . . enough questions for now.

Thanks alot for your patience and expertise!
Mike

The balanced power system is only permitted in commerical or industrial occupancies. See 647.3(1).
The equipment grounding conductor is required by 300.3(B) to be in the same raceway or cable as the power conductors. On high amperage circuits a remote equipment grounding conductor will have a high impedance because of the inductive reactance.
Don

Don,

Thanks for the reply . . . I know of several companies that market balanced power systems for the home studio market. Do such products then represent code violations?

So running the IG conductor in its own conduit breaks 300.3(B) . . . and running the IG conductor w/ the power conductors cause high impedance (which I understand contributes to line noise).

So why is running the IG conductor in it's own conduit unsafe?

Not trying to annoy, just fully understand why the code is there to begin with.

Thanks,
Mike

Oops, you miss read Don's reply. Go back and read it and you will find out that running the ground separately causes a high impedence grounding situation. This is a big problem during a fault condition and may cause the circuit breaker (or fuse) to not be able to clear the fault which would lead to a fire. When the ground is run in the same conduit this is not a problem.

A ground conductor that is dedicated to the equipment it serves or otherwise isolated from other loads it will not cause noise problems but will help clear them up.

Shane

Mike,
Are these balanced power supplies for home use permanently installed or is everything cord and plug connected? If they are cord and plug connected, they are outside the scope of the NEC. If they are hard wired, they are a violation of 647.3(1).
As far as the EGC, the code requires it to be run with the circuit conductors. In a low amperage circuit, the impedance increase is not really great enough to prevent or even slow the operation of the OCPD (overcurrent protective device) as long as the EGC is not in a magnetic raceway. In a magnetic raceway, choke effect from running a single conductor in a ferrous raceway could effect the operation of the OCPDI don't see how running this conductor by itself would change anything as far as noise goes. The only source of noise is that from the circuit conductors and the equipment itself. How could running the ground remotely decrease the noise generated by the circuit and equipment.

I did one studio for my brother. The building was already on a subpanel seperate from the house. Surge protectors were used in the sub panel and main panel. We used 20a 12g circuits for recepticals. They were not dedicated or isolated ground. The recepticals were not shared with anything elce. I think he had a power conditioner as part of his sound board. No Dimmers or floresent lights in building. No problems.

Tom

Thanks alot,

Judging from your replies, it seems that just running a couple dedicated 20A branch circuits with heavier gauge wire may do the trick. But would connecting them to a subpanel be even better?

After reading this:
http://www.equitech.com/support/techgrnd.html

It seems like having an isolated ground point in a subpanel (fed directly from the main service ground . . . not the bonded neutral/ground point in the main panel) would be even better. I could then run insolated curcuits whose ground was bonded straight to the main service ground.

BTW- that link is from one of the balanced power companies I mentioned and they cite NEC codes everywhere so they must have specific criterion for there products.

Am I getting any closer?

Thanks,
Mike

My two cents:

I think Paul's suggestion to used metal conduit is good. It will significantly reduce the electromagnetic field.

Another solution is to use braided wires. (I mean that the wires are braided together, not that the core of each wire is braided.) I don't know if you can find that in the US, though. As you will still have to use conduit (plastic), the metal conduit is most likely a better choice.

If you wnat the wires braided, you can use "BX" cable. The wires inside are braided, around 1 wrap per foot. And the metal armour would act as an electrostatic shield.

Also, shielded power cords are made (Belden) with shielding braid around the wires, with IEC connectors (like those on PCs). Those can help keep the hum down inside your equipment racks. The shield is connected to the green wire.

Oh, and don't pay $600 for the shielded power cords.