Quad Outlets and Power Strips with home run wiring

Velvet Elvis 2 · Post by **Velvet Elvis 2** » Wed Jun 14, 2006 11:29 pm

Steve,

I'm doing the electrical wiring in my studio with every outlet having its own home run back to the panel where the grounds are tied to the the ground bar (and nothing else) and everything else is tied to the same phase (minus lighting), as we discussed.

I started thinking about my racks - how do you handle outlets for say 25 units of audio gear? Do you actually need to put 25 separate outlets with their own home runs? As wouldn't using a power strip defeat the whole purpose?

Also - I assume where I have quad outlets, I need to make 2 home runs? One for each side of the outlets?

Thanks!
Jim

Post by **Aaronw** » Wed Jun 14, 2006 11:56 pm

Jim,

On the quad outlets, you can share the Hot & Common wires. But for Isolated Ground, each outlet has to have a home run ground wire.

Velvet Elvis 2 · Post by **Velvet Elvis 2** » Thu Jun 15, 2006 2:16 am

Aaron,

Thanks.. what about power strips in a rack? I am assuming this defeats the whole purpose of star grounding, but I can't imagine having 20+ outlets behind a rack.

Also.. even with home runs for the ground, every one outlet still shares a ground between the top and bottom outlet - Does that cause problems?

Thanks,
Jim

Post by **Aaronw** » Thu Jun 15, 2006 2:24 am

Thanks.. what about power strips in a rack? I am assuming this defeats the whole purpose of star grounding, but I can't imagine having 20+ outlets behind a rack.

You still want the star grounding, but yes, power strips and everything connected to it will then be sharing the same ground. Really though, you probably won't have any problems. Unless you have some old piece of gear that has some grounding issues, or voltage leaking to ground. If that's the case, you can always stick that piece of gear on a dedicated circuit.

Also.. even with home runs for the ground, every one outlet still shares a ground between the top and bottom outlet - Does that cause problems?

Correct. Problems, not usually except what I noted above.

For most outboard racks, you'll be fine using power strips, etc. But for large items such as power amps, 2" tape machines, console power supplies, etc, it would definately be beneficial to run dedicated circuits for those items.

knightfly · Post by **knightfly** » Thu Jun 15, 2006 5:00 am

Think of this as a "size of the antenna" issue - the longer the antenna, the more you pick up. So a 1" long piece of metal that's the equivalent of probably #10 wire in cross-section, besides having an effective resistance of about 0.0001 ohms, might be able to develop maybe half a microvolt of hum (if that.) -

Where the problem comes in, is if you have several FEET of wire tying two supposed "grounds" together - the larger the resistance between these two points, the more likelihood of any current flow between these two points developing a VOLTAGE difference between the points, so the more 60 hZ hum that can develop.

A power strip would have essentially zero ohms between ground points, and if it has only a 6 foot cord on it then you'll still only add a small fraction of an ohm in the ground line - so if that strip plugs into an isolated ground, then the most discrepancy between ground points you'd have would be that caused by the short cord on the power strip; and as Aaron said, it would be rare if this were enough to cause audible problems.

I've used metal racks in my studio for years, so each piece of gear has two ground paths; one through the mounting/rack, and one thru the power strip - all power strips were connected to a 4-plex outlet mounted in the back of the rack; each duplex receptacle in that 4-plex box has its own switch mounted on the bottom front kick panel of the rack with a DIY guard around it (so I don't accidentally kick it ) - this allows me to connect the power amps to one switch and the rest of the gear to the other for thump-free turn on/off. The noise floor with that setup is so quiet that with a mic up (in the middle of some nights) and the system output being monitored by an HP AC voltmeter set at -80 dB, I have to stop breathing in order to get the meter to settle down.

Bottom line - Again, Aaron covered it; you're using plastic boxes so they won't tie your two duplex outlets together, so do a home run from each duplex receptacle (two from a 4-way box, IOW), keep cords to power strips short, keep any "wall warts" as far away from signal wiring as possible, and you should be golden... Steve

Velvet Elvis 2 · Post by **Velvet Elvis 2** » Thu Jun 15, 2006 5:34 am

You guys are awesome.

That is EXACTLY what I did.

Every outlet in the studio has its own home run.

The outlets that will be carrying amps/computers etc have their own circuit. Though I did only use 15 amp cicruits.

All of the outlets in the studio, drum room, live room and vocal booth are on one phase. All lights and other outlets for the basement where the studio is are on the other phase.

The home runs have to run about 20 feet to the panel, which means loads of $$$ in high wire costs right now, but I wanted to do this right.

So.. I think given the following:

1) Plastic boxes
2) Home runs to each duplex back to the panel
3) All studio power outlets on one phase - grounded at the breaker panel
4) All other outlets and lights on the other phase - grounded at the breaker panel

I think I should be ok (at least as good as possible without dropping new service to the house), yes?

Thanks guys!
Jim

knightfly · Post by **knightfly** » Thu Jun 15, 2006 8:10 am

Rock 'n roll

(You're NOT using aluminum wire, right?)

Velvet Elvis 2 · Post by **Velvet Elvis 2** » Thu Jun 15, 2006 8:22 am

You're NOT using aluminum wire, right?

Not that I'm aware of... it should be all copper.

I'm ok having several circuits without worrying about getting shocked etc right? Since they all share common ground at the breaker? I'm recalling times of going to sing in a mic during a live show and getting shocked because there was a different circuit powering the stage versus the PA equipment.

I've got 4 circuits in the control room (3 quad outlets, each with their own circuit and then 3 duplexes as per code around the rest of the room on another circuit). My drum room is on another circuit and my vocal booth on another circuit. Lights for all three room are on the same circuit, but different phase than the wall boxes.

Just wanted to make sure someone singing in a room while holding a guitar plugged into an amp that is plugged into a separate circuit isn't going to fry themselves.

Jim

knightfly · Post by **knightfly** » Fri Jun 16, 2006 9:23 am

These shocks typically happen because of two dumb things - one, having some stuff plugged into the OTHER phase of power, so that there is a potential of having 240 volts across two devices, and (two) un-knowing or stupid people clipping or otherwise defeating the equipment ground, combined with attempting to minimise hum by flipping the "ground" switch common on some amps.

The combinations of those two events can cause up to 240 volts difference between chassis, and even if everything is on the SAME phase a lifted ground can cause the strings/bridge of an electric guitar to be at 120 volts relative to the wind screen of a mic, assuming that the mic's body is connected to the shell of the XLR plug and the shell of the XLR is connected to the shield, which is in turn connected to the shell of the OTHER XLR on that cable and it's then plugged into a PROPERLY grounded mixer.

Same phase for everything, don't mess up/defeat grounding; shock-free... Steve

Velvet Elvis 2 · Post by **Velvet Elvis 2** » Fri Jun 16, 2006 10:47 am

Electrician finished today...

All studio outlets are on one phase of the subpanel... the rest of the basement and the studio lights are on the other.

Each outlet in the studio has its home run back to the subpanel.

Went upstairs and checked the breakers of the main panel (which feeds the subpanel), and luck would have it that with the exception of the house AC, dryer and the stove (which are on both phases), EVERYTHING else other than general lights/outlets seemed to fall on the opposite phase as the studio.

Whirlpool, washer, microwave, loft A/C unit, refrigerator etc... all on the phase opposite the studio.

So.. for a 240 (two phase 120) home, I think I probably have it about as clean as I can get without using isolation transformers and such. I'm pretty stoked about it!

Clean, grounded power!!! yes!

Jim

Post by **Aaronw** » Fri Jun 16, 2006 1:27 pm

So.. for a 240 (two phase 120) home

Actually, it's still technically called single phase.

Velvet Elvis 2 · Post by **Velvet Elvis 2** » Fri Jun 16, 2006 1:30 pm

Picky picky!!

I'm just a dumb guitarist who programs computers to pay the bills... just tell me I did the wiring the right way on the studio and I'll be happy no matter what kind of phase its called! haha

Jim

knightfly · Post by **knightfly** » Sat Jun 17, 2006 1:35 am

OK, now yer jist tryin' to "save phase"...

Awright, fine, ya done good, fer a dang guitar picker...

Velvet Elvis 2 · Post by **Velvet Elvis 2** » Sat Jun 17, 2006 4:23 am

Wow... that pun was sooo bad that I can't believe you're making fun of *me*!! hahaha

Cool... glad I did it right.

Got the bill for the wire changes today from the electrician... OUCH!

Raised the whole bid by 33%!!!

Oh well... do it right or don't do it at all, right?

Jim

Post by **Aaronw** » Wed Jun 21, 2006 7:52 am

Raised the whole bid by 33%!!!

It's probably the increase in the price of copper. 3 years ago, a 500 foot roll of 12 AWG Solid was $18.00. Last week it was $60 for the same damn roll.

At this rate, gold will be cheaper to install.