2. tech-talk
  3. 1253131918

The Downside to Dedicated Lines vs. the Benefits

From an AC power grunge perspective, my main system currently seems very quiet. That is, I don’t have any ground hum issues, and I have to raise the gain fairly high and then get my ear quite close to one of the speakers before I can detect any hiss or other noise. It is truly the quietest system I’ve ever had experience with. Never the less, I do know that paying attention to AC power issues can reap other benefits, including an improved soundstage, imaging, better dynamics, etc.

I built this system from the ground up about a year ago and am now at the phase where I’m beginning to work on optimizing it. Back when I started planning it out, there was no question that I would be putting in a couple of dedicated lines. However, now that I’m at the point where I’m about to begin the project, and after a ton of reading and research, I’ve begun to have some serious reservations.

My concerns are mainly over the potential for introducing (or increasing) ground or ground-loop noise and/or hum. From what I can gather, powering interconnected components (especially non-balanced, or single ended, components) from multiple circuits, whether dedicated or not, raises the risk of this occurring.

I also understand the type of components as well as the system’s overall configuration plays a part as well. If I could summarize the details of my system and get some opinions about whether I run the risk of messing with an already good thing, I’d be very grateful.

The majority of my gear sits in a metal rack (Middle Atlantic) in an enclosure located directly behind the front wall of my listening room. XLR cables feed through the wall to a couple of mono amps that sit in the listening room near the speakers. The system currently doubles as a HT and 2ch rig and, as with most folks here, will no-doubt evolve and experience its share of equipment changes. As such, there’s a good chance I may not have a fully balanced system at any given point in time.

Right now, all of the audio gear, a cable box, an active sub, and a 60” plasma TV run off of one 20 amp circuit. There are various other wall-wart devices using the circuit as well (computer switch, rack fan, the receiver for my RF remote control, etc.) There might be a couple of incandescent lights that run on it too, but no other devices or equipment.

Everything currently runs through a couple of top-of-the line Belkin ‘Pure Power’ UPS/Surge Suppress/Conditioning units. Plans always were to repurpose these units after the dedicated lines were installed. However, considering the virtual lack of AC grunge despite all that’s plugged into them, I’m amazed at what these units are capable of.

If I do go ahead with installing the dedicated lines, I would put in a 100 amp sub-panel in the room that houses the rack. I’d need to pull about 80 feet of wire back to the main panel. (BTW, I don’t know much about the electrical trade, so if someone could offer guidance on what type of cable and gauge I should run, I’d appreciate it.) I’d then run 10/2 cryo’d romex (just because) out to three or four audiophile grade duplex outlets. Unfortunately, with where I’d be putting the sub panel, an isolation transformer wouldn’t be practical.

I would like to keep the existing branch circuit in place, and plug all the non-audio gear into it via the existing Belkin units (wall warts, cable box, TV, etc.) The front end equipment, sources, sub, and amps would go on the dedicated lines… directly at first…but eventually I’m sure I’ll end up trying one or two of the better power conditioners that are often sold here on Audiogon.

Now…from all that I’ve read, it appears that the above configuration could be prone to ground noise/hum issues. If I’ve correctly understood a publication that Middle Atlantic has out, a large part this potential comes from the fact that the metal rack serves to interconnect all the components stored in it.

What I’m concerned about is this. Since these interconnected components will be plugged into different circuits…i.e., a branch circuit that terminates at a panel 80 feet away, while the rest will use dedicated circuits that terminate a few feet away at the sub panel….will I end up with ground loop noise issues? As I said, the system is already very quiet and I would hate to lose more than I would gain.

Is there any wiring strategy that might help avoid it? I’m not sure I exactly understand the concept, but if I told my electrician to ‘star ground’ the dedicated lines, would that be enough? Should I instead think about putting the subpanel closer to the main panel? On the other hand, would it be better to not risk it and instead invest in one of the uber-top of the line power conditioners, or perhaps a power regenerator?

Whatever opinions or advice I can get from the Audiogon community would be appreciated.
shutterman
swampwalker's avatar
swampwalker
5,138 posts
 
Shutterman- the critical words are

"When this rackmounted equipment is screwed to the rackrail,..."

So in an all metal rack, with power cord grounded to chassis, IF every chassis is screwed [aka grounded] to rack, they will all be grounded to each other. OTOH, if you do not rack mount the equipment (or use plastic washers between the chassis and the rack and between the chassis and the screws) they will not be grounded to each other, unless the interconnects make the ground connection.
jea48
4,413 posts
 
Unfortunately, I think your opinion lines up with mine and gives me reason to believe that a multiple circuit (dedicated or not) might cause more issues than it would solve.

BTW, I noticed your comments were specific to equipment connected via IC's. What about the notion that in a metal rack, ALL the equipment loaded into it is interconnected...whether interconnects are present or not? Or am I reading too much into, or not properly understanding,this publication from Middle Atlantic?
Not really.... My comments are in regards to using the existing 80 ft 20 amp dedicated branch circuit and branch circuit/s from a sub panel with an 80 ft feeder to feed equipment that would be connected together by ics of equipment fed from the two different fed power systems. Has nothing to do with rather the equipment is rack mounted or not.
>>>>>>>>>>>>>>

Isolated ground power strip in a non-isolated rack (cont.)

A problem will exist due to the fact that all equipment with a 3-prong (grounded) plug has the power cord ground conductor bonded to
the chassis. When this rackmounted equipment is screwed to the rackrail, an inadvertent ground connection will be present, defeating
the isolation!"
In the above quoted info the author is talking about commercial building power wiring situations. Problems a person would not normally encounter in a single family dwelling unit, imo.

You are not going to use an isolated ground system are you?

If you install a sub panel, as you said, about 10 ft from the rack I see no problem.

Branch circuit runs will be short, less than 20 ft. (Figuring up and down or around.)



80 ft? Is that straight as the crow flies? Did you figure up, down, and around?

In the sub panel you will have an isolated neutral bar and an equipment ground bar. Sizing all conductors the same will a sure both the neutral bar and the ground bar will be at the same ground potential.

So if you are worried about the possibility of the neutral conductor and equipment grounding conductor not being at the same ground potential at the sub panel make all the feeder conductors the same size....

Minimum size feeder wire I would recommend, #4 awg copper. Breaker size 60 or 70 amp.

Electrical panel, copper bus only..... No aluminum bus.

shutterman OP
7 posts
 
Swampwaker…Thanks for pointing out the wording in that section. It made me think about exaclty how the equipment is loaded in my rack. Each piece is, in fact, not bolted to the rail. However, each piece is pushed up against a custom cut metal face plate that MA sells. These faceplates are then bolted to the rails. I started out using the insulating washers, but they were somewhat "fiddly" to deal with, so I wound up with just a few of them. I'll now probably go back and make sure they are installed on each one.

And…just to provide a little more assurance against a ground loop from forming, I think I’ll abandon the idea of trying to use the existing branch circuit coming off the main panel to power the non-audio gear. Seems like it would be better to simply install an additional circuit or two off the sub-panel.

Jea...no, I wasn't planning an isolated grounding scheme. However, just out of interest I read up a bit more on the subject last evening and have a better understanding of its commercial application. I see now that MA's white paper is, as you pointed out, geared more toward that type of install.

The 80' back to the panel is the up, down, and around estimate. Estimate includes some slack, so the feeder wire could turn out to be shorter. For the circuits off the sub panel, I estimate the longest run to be about 20', shortest run could be as little as 8', depending on cross stud placements we encounter in the wall. That is…unless there is an audible or electrical advantage to keeping the runs the same length?

The deal I have with the electrician is that I will buy and have on hand all the materials. Consequently, I’m doing my own research on what all will be needed. Concerning the sub panel… I started out thinking a Square D QO product, but think I’ve instead settled on a 100 amp Cutler Hammer CH panel. According to their product literature, the CH series uses a “Single-Piece Silver Flash-Plated Copper Bus”

My main panel is a CH 200 amp box. I have only two-breaker slots left available on this panel, which is the reason for the sub-panel decision. I have 20 amp breakers in the main, and I plan to use 20 amp breakers in the sub panel also.

One question I haven’t nailed down as yet: Do I need to buy both a 100 amp (or, perhaps the 60-70 amp you mentioned) breaker for one of the two available slots on the main panel AS WELL AS a 100 Amp main breaker at the sub panel?

BTW, thank you for your tip about making all the wiring for the circuits off the subpanel the same AWG. I had thought about using 10/2 for the mono amp circuits and 12/2 for the rest. Your advice about not using a mixture of AWG is appreciated.

A couple of final questions if you don’t mind…with a 100 amp subpanel in mind, the electrician had recommended a #3 AWG copper cable for the feeder line. I assume this means a 3 conductor solid core cable with safety ground wire…right? That is, when I give the big-box store man my order, I shouldn’t have to specify much else? In other words, I don’t need to purchase a separate ground wire also?

As far as trying to keep everything in the sub panel on the same leg is concerned…since it is being fed from only one leg off the main panel, does this mean that each and every breaker row in the sub panel is therefore also on this same leg? In other words, there’s no need to skip breaker rows in the sub to ensure the all the audio gear is fed from the same leg?
jea48
4,413 posts
 
One question I haven’t nailed down as yet: Do I need to buy both a 100 amp (or, perhaps the 60-70 amp you mentioned) breaker for one of the two available slots on the main panel AS WELL AS a 100 Amp main breaker at the sub panel?
The sub panel does not need a main breaker. Buy a main lug only load center.

BTW, thank you for your tip about making all the wiring for the circuits off the subpanel the same AWG. I had thought about using 10/2 for the mono amp circuits and 12/2 for the rest. Your advice about not using a mixture of AWG is appreciated.
That was someone else but I agree..... As short as your branch circuit runs are you could use 12-2 W/G for all the branch circuits.The electrician would probably give you a big hug as well....
8' to 20' branch circuit runs, call me cautious but I would try to keep them with in a couple of feet of each other. No coiling up though...

A couple of final questions if you don’t mind…with a 100 amp subpanel in mind, the electrician had recommended a #3 AWG copper cable for the feeder line. I assume this means a 3 conductor solid core cable with safety ground wire…right?
Per UL for sizing the over current device,(breaker), for #2 awg wire and smaller use the
60* C column. #3 awg THHN/THWN copper wire is good for 85 amps.
If you look inside your 200 amp panel some where on the side you will see an info label. The label will say what the maximum allowable size branch circuit breaker that can be installed in the panel. Just guessing 80 amp. Check your panel.
In most cases the lug size on a 60 amp breaker is for a maximum size wire of #4 awg. You would have to use at least a 70 amp breaker for #3 awg wire. The maximum lug size for a 70, I believe, is #2 awg.

#3 awg wire will be stranded.

As far as trying to keep everything in the sub panel on the same leg is concerned…since it is being fed from only one leg off the main panel, does this mean that each and every breaker row in the sub panel is therefore also on this same leg? In other words, there’s no need to skip breaker rows in the sub to ensure the all the audio gear is fed from the same leg?
Are you feeding the sub panel with 120V only or 120/240V?
If 120/240V every other breaker down each side is the same Line, leg.

Future? I would probably feed the panel 120/240V
2 hots, 1 neutral, 1 equipment grounding conductor.
Jim

shutterman OP
7 posts
 
Are you feeding the sub panel with 120V only or 120/240V?
If 120/240V every other breaker down each side is the same Line, leg.
Hmmm...good question. When the electrician scouted the job, he took a quick look at the panel. He said that he would use one of the two vacant slots in the panel to tie the feeder line to. Don't know if he specifically checked the info on the panel door or not, but it was he that came up with the recommendation for a 100 amp sub panel. He told me specifically that I'd need to get a 100 one-way amp breaker for the main panel. (I take it that he meant a single pole 100 amp breaker.)

He also said that I should have a 100 amp main breaker in the sub instead of a lug only load center. But after thinking about it later, I couldn't see the need for it, so that's why I threw the question out here.

I thought because he would be tying into only one place on the main panel...using only a single pole breaker...that this meant the feeder line was tied to only one leg, and therefore only 120v. On the other hand, he did specify the feeder line needs to be a 3 conductor wire, so perhaps he does intend to feed 120/240V? If so, I'll be sure to use every other breaker in the sub panel in order to keep everything on the same phase.

I think my next step is to work out some of the above details with the electrician that's going to do the job. No need to expect folks here to take up anymore of their time to help fill in gaps that I can run down by other means. However, I couldn't have got this far without the help of Jim (Jea) and others who provided guidance. Nice thing about forums with decent search engines like this one is that threads like this can help other folks down the line for a long time to come.

I think I've learned that while there's a strong argument for using only one dedicated circuit to feed all interconnected equipment, others find advantages in having all analog and all digital on separate circuits. If a single dedicated line isn't practical, it would seem adviseable to at least branch all lines for interconected components from the same panel in an effort to avoid ground loop issues. Wiring phase for both the lines and the equipment is an important part of the equation and needs to be checked. And finally...in spite of what smattering of knowledge a laymen might gain, wiring in additional electrical capabilites is serious business that's best left up to a certified pro.

I'm sure there are several other points others have made that I failed to mention. I'm also sure there are a dozen other aspects that haven't been brought up, so if anyone wants to chime in with other pointers, I'm certainly willing to listen.
More to discover