question on dedicated power lines

[tpaxadpom]

How many dedicated power runs do you have in your setup? I plan on having 5 20A runs from the circuit breaker to dedicated stereo room and 3 20A lines to my HT setup. The question I have is whether it's common to have ground loop problem with dedicated lines or not.

[Anthony]

I have 2 dedicated. 1 15 amp, and 1 20 amp (single plug). In my case, I'm close to the breaker panel, so grounding isn't a problem.

you may be surprised how little many HT components draw. Power amps being the noticable exception. You may find all those dedicated lines are unnecessary. Do you have an equipment list? If you need lots of plugs throughout the room, they can be on the same few circuits. One 20 amp circuit is good for 2400 Watts sustained. If you have/need more than that then of course, you need extra circuits.

Just trying to save you some money and headaches

[Anthony]

Oh, and if they all tie in at the same sub panel or main panel, you should be fine on grounding. Ground loops are usually a problem between external signal and power or power circuits that are on separate sub-panels.

[tonyvdb]

Dont get too carried away with to many dedicated circuits, I have two 15 amp circuits and have taken an amp meter to both of them during high demand audio at reference levels and barely draw 6 amps on the one and only 4 on the other.

[tpaxadpom]

I have the equipment list.

I'm not a big fan of power filters (they all degrade sound quality one way or the other imho) that's why I want to have 5 dedicated runs for stereo room (premp, power amps, DAC and transport). Not so much for power consumption. According to current meter on monster power center my stereo consumes around 5.5A (in ideal condition when power factor is 1, current and voltage 90degrees out of phase), that would equal to 5.5x117=643.5W (117V due to slight voltage drop due to wiring resistance). Currently 15A braker is feeding 3 bedrooms. I plan to keep my subs on original wiring. Power consumption in HT is about the same when I watch Blu-Rays on PS3.

The wires are cheap (I won't buy cryo treated wire) I checked at home depot. I need about 70-75ft for each run to stereo room and about 45ft to HT room. 10 gauge 250ft $92 and a little more for romex brand.

Here is the list of components.

[brucek]

I plan to keep my subs on original wiring.

It's important to keep all the dedicated circuits on the same leg in the service panel to avoid ground loops. Be sure that you use the same leg that the circuit for the subs use.

brucek

[Ryan-T]

20 amp lines are 12 gauge not 10.

[tpaxadpom]

brucek wrote:

It's important to keep all the dedicated circuits on the same leg in the service panel to avoid ground loops. Be sure that you use the same leg that the circuit for the subs use.

brucek

Thanks Brucek. I will definitely do that. I've noticed that it's mostly appliances connected to the second leg.

[tpaxadpom]

Ryan-T wrote:

20 amp lines are 12 gauge not 10.

I know that the most common code is 12 gauge for 20 A and 14 gauge for 15 A (that's how my house is done), but I am trying to go with heavier gauge. If I had a way to fish 5 lines of 6 gauge wires (I believe code requires single core, not stranded) from the basement to the second floor I would go for it. I can not think of any 15, 20 A receptacle that would accept that gauge.

[brucek]

I know that the most common code is 12 gauge for 20 A and 14 gauge for 15 A

Rule of thumb usually demands stepping down a guage over ~50 feet.

Thanks Brucek. I will definitely do that. I've noticed that it's mostly appliances connected to the second leg.

Generally, they'll attempt to balance the load across the two legs.

I did want to comment that you may find that using an existing circuit for one piece of equipment (subs) and then using dedicated lines for the rest is a poor idea for several reasons.

The existing receptacles may have up to 12 lights and receptacles on the same circuit. At each receptacle that the wiring runs through, there is a set of twisted connections inside covered with wire-nuts that may be presenting a small resistance. The more of these connections, the more possibilities of poor, high resistive joints before the circuit reaches the receptacle that you are using. These connections can become highly resistive.
Not to mention the myriad of things like motors, fluorescent lamps, and computers that may also be plugged into this same circuit besides your system.
All this can result in a loss of power and increased noise at the receptacle you're using for your system.

There's also the very real possibility that the overall resistance of the safety ground through the existing circuit will offer a small potential that is different than the dedicated circuits. This small potential difference will cause a ground loop. And what better piece of equipment to amplify a ground loop than a subwoofer.

Although there's nothing magic about dedicated circuits, it ensures a single run of cable from your power panel to a wall receptacle, with no interconnections between and nothing else plugged into the circuit except your system.

When you use two or more dedicated circuits you do have the added possibility of ground loops, but it's far less than between a dedicated and an existing circuit. The best solution for this is to run the dedicated circuits from a common leg together so they are identical lengths and paths traveled. This helps to ensure the potential of the safety grounds are at the same value. The loop is caused by a difference in the safety ground potentials in the system. Even though the safety ground is a cold conductor, it always has a small potential across itself.

brucek

[tpaxadpom]

brucek wrote:

Rule of thumb usually demands stepping down a guage over ~50 feet.


Generally, they'll attempt to balance the load across the two legs.

I did want to comment that you may find that using an existing circuit for one piece of equipment (subs) and then using dedicated lines for the rest is a poor idea for several reasons.

The existing receptacles may have up to 12 lights and receptacles on the same circuit. At each receptacle that the wiring runs through, there is a set of twisted connections inside covered with wire-nuts that may be presenting a small resistance. The more of these connections, the more possibilities of poor, high resistive joints before the circuit reaches the receptacle that you are using. These connections can become highly resistive.
Not to mention the myriad of things like motors, fluorescent lamps, and computers that may also be plugged into this same circuit besides your system.
All this can result in a loss of power and increased noise at the receptacle you're using for your system.

There's also the very real possibility that the overall resistance of the safety ground through the existing circuit will offer a small potential that is different than the dedicated circuits. This small potential difference will cause a ground loop. And what better piece of equipment to amplify a ground loop than a subwoofer.

Although there's nothing magic about dedicated circuits, it ensures a single run of cable from your power panel to a wall receptacle, with no interconnections between and nothing else plugged into the circuit except your system.

When you use two or more dedicated circuits you do have the added possibility of ground loops, but it's far less than between a dedicated and an existing circuit. The best solution for this is to run the dedicated circuits from a common leg together so they are identical lengths and paths traveled. This helps to ensure the potential of the safety grounds are at the same value. The loop is caused by a difference in the safety ground potentials in the system. Even though the safety ground is a cold conductor, it always has a small potential across itself.

brucek

Brucek,

thanks a lot, all of these are very good points. I would run dedicated runs to my subs but it's not practical in my case as the room is finished. One possibility is to run extension cord for the subs (not very pretty though). I don't use AV processor in my stereo system and have no means to control group delay of main speakers or subwoofers. I thought of getting DEQ2496 to play with time delays, but I didn't get a clear answer on this forum nor behringer tech support wether that configuration will work (manual isn't very useful to answer that question and I will have to invest in the second preamp to control the volume on subs). What I've done is placed my subs next to the couch as otherzise they lag main speakers. This configuration seem to work fine. I will verify group delay once new version of REW will come out. I feel safe that powering subs of the current circuitry is fine as they don't have safety ground. The most common issue like you've stated is due to safety ground potential differences. My preamp has 2 sets of single ended and one set of balanced outs. As I don't run balanced connection from my DAC to preamp and don't use active mode on my preamp I can not benefit from balanced connection.
Overall it seems pretty safe to have multiple runs if the cable lengths are about the same and there are no serious EMI issues (electrical cables are not shielded/twisted).
Another option is to combine safety grounds on dedicated runs (allowed by code according to some but I haven't confirmed that with an electrician) in case of the ground loop problem. I remember when I live in appartments I had ground loop problem formed with cable TV. I connected safety ground to shielding on the coax and it did lower amount of hum but not eliminated it completely (I ended up running it through monster power center that use isolation transformer inside). BTW I don't recommend anyone connecting safety ground to coax shield as it's not safe!
I will have to make sure that loads distributed somewhat equally in the breaker box. Perhaps this will require rearanging the current setup (moving some loads to a different leg).