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How to disperse avail. amperage?

I am going to soon be the proud papa of a designated listening room. Yes, it is the culmination of a 30+ year dream, but that's another thread. My question is : how exactly do I "divvy-up" the available electric into the room? I am converting a 13' x 18' detached garage which started out as uninsulated studs on the interior only shell, on a concrete slab. The exterior walls are approx 3/4" planking (built in the 1940's) with recent vinyl siding. I built a shed to house all the important stuff and ditched the rest. I had a new roof put on, as well as new leaders and gutters. I also had a side entrance door installed. I plan on removing the worn main 'big' door and removing the interior tracking for it, then i nstall a new dummy door, permanently affixed. Inside that I'll stud out an interior shell wall , then insulate and drywall it. I am well on my way with much of this already. I'm having an electrician come today to discuss running a 125amp sub panel from my main house's [recently upgrade] 200amp panel, out to the garage. this will include an 18" trench to run the cable, and I'll probably add a "cable box" cable too...When I have the box installed it'll be 125 amps. I'm expecting the main breaker on the house side of it to probably only be 100 amps? as well as the main breaker on the sub panel to only be 100 amps too... mostly because the 100 amp breaker is 1/3 the $300 cost of the 125 and I can't imagine I'd be drawing that much current all at one time?
I would like to have a separate breaker for "all lighting", as I plan on using dimmer switches and a reasonably extensive amount of light.
I will also be installing at a later time, when $$$ allows, a ductless A/C & heating system that can use a 15amp service (draws 11amps max). I was thinking it would be nice to actually provide a 20 amp line to this if I had the extra available.
I want a dedicated line for my analog pre, turntable, and analog misc (my electronic crossover)
I need a dedicated digital (multi players, Dacs , jitter boxes, SACD, etc
And since I am TRI-amping my speakers I need a dedicated for my tubed monos
A dedicated for 2 sub amps
A dedicated for my mid/tweeter amp
At 20 amps for each, except the lights,this adds to 120 plus the lights. Can I use a 10 amp on the lights for a total of 130 and be OK? Should I lessen the digital or analog only to a 15A for one of them? Any combination you can imagine would be a helpful suggestion. Thanks! Happy Lissn'n
lissnr
jea48
4,666 posts
 
I also bought the optional ISOLATED grounding bar for it.

Why? An isolated ground bar will serve no purpose. I imagine the panel enclosure will be mounted to wood studs and the branch circuit wiring will be NM-B cable. (Romex is an example of NM-B).

How does your electrician plan bonding the panel enclosure to the main electrical systems equipment ground? Is he going to install two equipment grounding conductors from the main electrical panel to the sub panel? One for the isolated equipment ground bar and one for the panel enclosure?

The most serious deviation from all our discussion is that because I'm only running a 70Amp main breaker (into the 125A panel) my electrician and the guys at the electric supply store told me 2G wire is way overkill and that 4G can handle 100A service so I shouldn't waste my $$$ on the 2G and just get the 4G... which, although I was hesitant not to continue with "over-overkill everything"... I decided to do the 4G.

NEC 2005 Table 310.16
#4awg 60 C is good for 70 amps, not 100......
Because of the distance from the main electrical panel to the sub panel I would have stuck with the #2awg minimum.

my electrician and the guys at the electric supply store told me 2G wire is way overkill and that 4G can handle 100A service

The guys at the electrical supply store are not electricians.

Did you ask to see your Electrician's Electrical License?

You are not installing an electrical service. You are installing a feeder and a sub panel. NEC does allow # 4awg for a 100 amp electrical service. But in most cases the service entrance conductors are less than 25 ft.

In your case the larger feeder wire is for voltage drop due to the air conditioning load, small refrigerator, as well as the dynamic demand your audio system's Power Amp/s
may present on the feeder. You want the voltage not to fluctuate with load changes as much as possible.

I also didn't skimp on the ground for it... while everyone told me the ground cable can be one size smaller than the main ones,


I think they confused the neutral, (The Grounded Conductor), with the equipment ground, (The Grounding Conductor).

NEC 2005 Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment.

70 amp breaker - minimum #8 awg copper.

I said go with a #6 but I think for an audio system a larger wire would probably be better.
lissnr OP
365 posts
 
Uh oh? The term "Voltage drop" can send shivers down my spine...Assuming this 4G wire couldn't possibly be returned, as it's already cut, it sounds like I can do at least 2 things to minimize the voltage drop:
1) "Pre-cool" the room w/ the A/C before I go in to listen (which is what I normally do anyway due to the noise)as my amps are warming up (about 1/2 hour which should be plenty)
2) Forget about the small refrigerator completely (I shouldn't be promoting liquids in the room anyway!) (or, worst case, have a plastic beach cooler instead).

"...as well as the dynamic demand your audio system's Power Amp/s may present on the feeder. You want the voltage not to fluctuate with load changes as much as possible."

The overall [cable length] distance from main box to sub panel will be about 50' (twice the 25' you had mentioned)...W/ no A/C [or refrigerator running] can I feel pretty confident that I won't have a noticeable drop (if any at all) in power to my system at this distance/scenario? At this stage of the game, if I have to consider $400 of cable (I bought extra extra length to be sure not to have underestimated) a worthless stack of novice blunder...then pay an additional $4-500 for the right stuff (the 2G)...now's the time to do it. I'll bite the bullet if I have to... especially if this is fundamentally critical to the best sound my system can deliver...In the big picture of things, it's like getting stuck with a new I/C or P/C that didn't synergize with your system but simply can't be returned (or ever re-sold!) ouch!! (but I'd really rather not!)

As for the separate ground...I'll ask my electrician (who came highly recommended from a contractor friend of mine)and who claims to be fully licensed...what I will do there. The Hubbell I/G outlets can still be used anyway, yes? Even if they're simply grounded back to the sub panel's standard grounding bar?

Yes, the sub panel will be affixed to 2 sheets of 3/4" plywood attached to the wood walls (I'm using 3 sheets of 5/8 drywall on all the main walls for sound proofing purposes and I need the 2 pieces of 3/4" ply to get the cover of the panel out enough to be about even with the drywall).

Needless to say, I'm anxiously awaiting your advice.
Pensively. Thanks again.
tonywinsc
583 posts
 
At the beginning you mentioned installing dimmers. Dimmers are bad for RFI. I'd recommend just using lower watt bulbs and/or more light switches to turn on seperate lights for progressively more lighting. Possibly even use low voltage lighting when listening for a softer ambient feel.
jea48
4,666 posts
 
The overall [cable length] distance from main box to sub panel will be about 50'
That's a far cry from 110' you posted earlier......
If the run is only a total of 50' then #4awg copper should be fine.

As for the separate ground...I'll ask my electrician (who came highly recommended from a contractor friend of mine)and who claims to be fully licensed...what I will do there.
Ya, post back his response if you would.

The Hubbell I/G outlets can still be used anyway, yes? Even if they're simply grounded back to the sub panel's standard grounding bar?
Unless you just like the orange color of the receptacle why did you spend the extra money for isolated ground receptacles?
Isolated ground receptacles are used in commercial and industrial facilities where EMI noise on conduit, metal studs and steel are a problem. I assume you will be using wood studs with MN-B cable and plastic rough-in boxes.

Essentially the non IG Hubbell will work just as an IG ground type in your instance.

For the Power Amp/s I personally would go with the Hubbell HBL8300H ("H" stands for non plated)
jea48
4,666 posts
 
I would recommend "Lutron" Dimmers!
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