Wiring a new home: separate meter boxes

**John Simpson** · **06-15-07, 10:22 PM**

Does anyone have experience wiring a new home with a dedicated home theatre room?

I have heard it's best to put the HT room on it's own circuit -- does that mean you still have one meter box, but two separate fuse boxes? Or two meter boxes? Or a single meter/fuse box, but run the electricals separately?

Thanks!

**brucek** · **06-16-07, 06:34 AM**

Quote:

Or a single meter/fuse box, but run the electricals separately?

Most electrical circuits in a home service a number of lights and receptacles. Your local regulations determine just how many of these drops are allowed on each circuit.

The recommendation for a hometheater though is to run a few circuits that are dedicated to the theater alone. The dedicated circuit uses a single run of cable from the service panel breaker to a single receptacle in the theater. Two or three of these dedicated circuits would be suffice. The dedicated circuit ensures there are no other devices (other than your theater electronics) plugged in along the way to the theater to create noise. It also ensures there will be no high impedance connections in other receptacle boxes along the way, and also no lights will be on the circuit.

The lights for the theater would be on a separate circuit(s) to your dedicated circuits...

No separate fuse boxes, meter boxes etc. Just a single run of cable to a single receptacle.

brucek

**Otto** · **06-16-07, 09:12 AM**

I generally agree with brucek's assessment, but I don't think I would insist on a single cable run per receptacle. For example, I know a friend that has two receptacles on one wall, and those are on the same dedicated cicuit. If I were doing a new HT, I would probably put in two 20 A dedicated circuits for the room. Lights would be on another circuit, and so might other receptacles that would supply other stuff that's not HT related. Something like that...

**Sonnie** · **06-16-07, 09:31 AM**

That's what I did, but I also didn't have a lot of choice in the matter, since we built our home prior to building the dedicated HT room. Fortunately I stubbed up a few extra circuits into the attic for future use when I wired the house. I used one for the receptacles and one for the lights. No problems thus far.

**brucek** · **06-16-07, 09:33 AM**

Quote:

I know a friend that has two receptacles on one wall

Unfortunately, then it's not a dedicated circuit. The connections inside the first receptacle box create an impedance that can result in a ground loop between the two receptacles.

brucek

**Otto** · **06-16-07, 09:42 AM**

I thought that might be the case...

**Wayne A. Pflughaupt** · **06-16-07, 12:00 PM**

brucek is correct. See this link; scroll down to “What is a dedicated line?”

That said, I’ve never seen a case in an audio system, professional, commercial or home, where adding extra outlets to a dedicated circuit caused any noise problems. When I was installing pro systems in large venues, we did it all the time, spec’ing say, a circuit for the processing electronics (EQs, crossovers, etc.) a maybe a circuit each for the high frequency amps, mid range amps etc. We paid attention to the total load on the circuit more than anything else. The company owner and primary system designer and was an electrical engineer, by the way...

In some cases we did do a “star grounding” scheme, with separate grounds for each outlet running back to the supply line, I presume to prevent the theoretical ground loop potential. That would be a bit tricky to pull off in a house, since you probably can’t use THHN for the extra ground leads (doubtful that it’s in-wall rated). But with a little imagination it could be done.

Regards,
Wayne

**lcaillo** · **06-16-07, 04:05 PM**

Quote:

brucek wrote:

Unfortunately, then it's not a dedicated circuit. The connections inside the first receptacle box create an impedance that can result in a ground loop between the two receptacles.

brucek

So are you suggesting dedicated runs to the panel for each outlet? Would this not have a greater impedance than the shorter run between the outlets? What about a dual gang box? Are the connections really a bigger issue than the run of wire?

**lcaillo** · **06-16-07, 04:09 PM**

To answer the original question...

A dedicated circuit is desirable. A second panel and meter are not and may not even be possible in the same dwelling under most electrical codes. Any connections (network, cable, sat, distributed audio/video, etc) between systems on the two meters could conceivably create a problem. The grounds would have to be bonded together to meet code at the very least.

**brucek** · **06-17-07, 05:54 AM**

Quote:

So are you suggesting dedicated runs to the panel for each outlet?

Yeah, that's what makes it dedicated. A single uninterrupted path to the service panel. If a second line is installed, then it must share the same leg at the service panel. Usually two 20 amp circuits would be suffice for most theatres. The lighting circuit can be the same as any other in the home.

brucek

**alan monro** · **06-17-07, 06:24 AM**

John. In America they only have 110volts so their cables have to be thicker than ours to run the same current , or , they run more cables. Our 2.5 mm will run about 15amps . I have never had any interference problems in my H.T. Why try to fix something that isn"t broke . Kind regards , Alan .

**Wayne A. Pflughaupt** · **06-17-07, 05:10 PM**

Quote:

brucek wrote:

Yeah, that's what makes it dedicated. A single uninterrupted path to the service panel. If a second line is installed, then it must share the same leg at the service panel. Usually two 20 amp circuits would be suffice for most theatres.

Hmmm... Seems like a real dilemma: Two dedicated circuits, by its “clinical” definition (for lack of a better word), only gives a total of four plugs. Most of us have way more stuff than that to plug in.

So what do you do? I know many people use plug strips (which I personally don’t care for). Does that get the same impedance that can cause a ground loop between two receptacles? It seems like it would – I can’t see a functional difference between splitting out extra plugs via a plug strip vs. connecting extra outlets in the wall. Either way, the outlets are all paralleled together.

Am I missing something?

Regards,
Wayne

**brucek** · **06-17-07, 05:28 PM**

Quote:

Most of us have way more stuff than that to plug in.

So what do you do?

Power center, power condition, power bar is fine. The close bus bar connections in them gives you good results.

brucek

**Wayne A. Pflughaupt** · **06-17-07, 05:53 PM**

Ah – so it’s the close connections that make the difference. Makes sense. How would a dual gang box stack up?

Regards,
Wayne

**brucek** · **06-17-07, 06:53 PM**

Quote:

How would a dual gang box stack up?

Yeah, I'm sure it would be fine. For sure wire length makes a difference, but the connections can be a problem too, especially when you enter and then leave a box with the twisted wires and the marettes on them (I think you guys call them wire nuts).

The idea is to have no connections between the receptacle where you plug the device in and the service panel. Some people (myself included), when they run two dedicated circuits ensure the two runs are an identical length to the receptacle to try and have equal impedance on the safely conductor, so as to try and remove as many chances of having a ground loop as possible.

The hope is that inside the power bar or power center that they have done a nice job of running close buses between the receptacles (a normal practice)...

brucek

**Danny** · **06-17-07, 10:10 PM**

John

Noticed you are in Australia, as we have 240 volt power here in Aust. i'd say probably two 10Amp dedicated circuits would suffice

**John Simpson** · **06-18-07, 01:09 AM**

So, when you say "receptacle", that's a single plug/socket in the wall, correct?

From what I understand, it looks like it would be fine to have a single 240V wire running from a fuse on the fusebox, to a series of sockets in the HT cabinet. Just so long as the wall sockets are close together, much like a powerboard.

For the wall sockets further away (eg: projector power) perhaps that would be better to have it's own wire to the fusebox? Well, that socket and maybe a few other spares, to plug the vacuum cleaner in, etc...

**gphall** · **06-18-07, 07:42 AM**

Quote:

brucek wrote:

Some people (myself included), when they run two dedicated circuits ensure the two runs are an identical length to the receptacle to try and have equal impedance on the safely conductor, so as to try and remove as many chances of having a ground loop as possible.
brucek

Trying to match the impedance on the safety conductors seems a very difficult issue. Keeping the run length and wire gauge the same would match DC Resistance, but impedance also includes Capacitive and Inductive reactance. Matching these would be much more difficult.
Keep in mind too that the safety conductor should have NO currents running through them. The whole purpose of those safety conductors is to carry ground potential from a single point (the service entrance) to the receptical , through the plug to the chassis of your equipment. If there is ANY current through this wire then the service entrance potential will not be equal to the chassis potential due to IR drop and the safety mechanism is defeated. This conductor should only have a current during a fault condition.

IMHO, keeping the run length as short as possible for a dedicated run and using the largest gause cable (within reason and meeting local codes) would be a better option. Ground loops existing across dedicated runs would seem to indicate a mis-wiring of the outlet rather than a problem with matching safety ground impedances.

G

**gphall** · **06-18-07, 07:43 AM**

Sorry for the mis-spelling. Largest GAUGE cable, not gause.

**lcaillo** · **06-18-07, 07:47 AM**

brucek,

While nearly every post you make has great info in it, I have to differ here on the significance of the impedance created by using two receptacles on the same circuit compared to wiring each back to the panel. The resistive component is smaller between receptacles even with the connections in the first box. The capacitive and inductive components are not significantly different. Wire nuts are typically not used at all in a jump run to a second receptacle (at least not in modern work in the USA). The second connection on the receptacle is used. This makes the type of connection not much different than the one in the panel, and the wire run typically much less.

I have never seen a ground loop due to a properly wired second receptacle on the same circuit in 30 years of HT installation and service work. The reason for a second run back to the panel is current capacity if it is needed, not to prevent ground loop interactions.

**brucek** · **06-18-07, 08:49 AM**

Quote:

This conductor should only have a current during a fault condition

Yeah, that would be great, but it just ain't so. Even though the safety ground is a cold conductor, it can and usually does, develop a small potential, through mutual inductance, RF bypass current and various other reasons that can be quite different at each receptacle in your house.

The result is that when you plug a power amp into one receptacle and a preamp into another receptacle, the metal cases of these two units can have a small potential difference in their safety grounds which means that this equipment's metal cases are at a slightly different potential. When you connect a single ended (RCA) cable between these two devices, a small AC current can flow in the shield because of the potential difference. This unwanted signal is in the signal loop circuit and can cause a hum.

An interconnect circuit has a loop path (completed circuit) that flows through the centre conductor of the interconnect cable and back on the shield. If there is an AC signal on the shield flowing because of the ground difference potential, you'll hear a hum. It's source is the safety ground. There's no fault, there's simply a reason for the safety signal that needs to be traced.

Quote:

Wire nuts are typically not used at all in a jump run to a second receptacle (at least not in modern work in the USA). The second connection on the receptacle is used.

Not allowed in Canada. The neutral and safety must be pigtailed with marettes (wire nuts) to allow the receptacle to be removed without affecting downstream circuit grounds. The second connection is to be used for split plugs only.

Quote:

I have never seen a ground loop due to a properly wired second receptacle on the same circuit in 30 years of HT installation and service work.

Fair enough. Over 32 years working in electronic engineering at large computer facilities has made me gun-shy of ground loops. It's such a simple task to run a couple dedicated lines to their own receptacles near your equipment and then wire the rest of the room normally, I can't find a reason not to.

brucek

**lcaillo** · **06-18-07, 09:44 AM**

Your circuit description is largely accurate, except that you are assuming a higher impedance between outlets on the same circuit than those that are on dedicated runs. This is simply not the case. Measure it sometime. The length of the ground path is greater for the dedicated runs back to the panel and the dominant component of the impedance is that resistive component. In fact, the other components are lower between outlets as well. As you know, any analysis is only as good as the underlying assumptions. In this case you are simply making a bad assumtion about the relative impedance. For prventing ground loops it is far better to just plug the units into the same outlet or same power conditioner/surge suppressor or whatever than to use separate dedicated runs, unless the current needed is exceptional.

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