Electrical Outlet

[eboettn]

Hey all,

I'm installing a dedicated power circuit for my home theater. My question is: what is a good electrical outlet to use? I've heard I should use hospital grade outlets, but does this really matter? Is there really a difference between that and pro-grade outlets at say home depot? And is there anything else I should consider doing to my circuit that would benefit the home theater?

Thanks all!

[servicetech]

Hospital grade outlets are fine, although it doesn't have to be that expensive. Look at a cheap 39 cent outlet and a high quality commercial grade one at your local electrical supply, you should be able to tell the difference visually. Be sure to use #12 awg wire and a 20A breaker.

Remember anything related to medical stuff is automatically marked up 300%.

[ThomasW]

The only difference between a hospital grade and a commercial grade outlet is the way the ground is broken when something is unplugged. Other than that the construction is identical.

[Geoff Gunnell]

Wiper contact area is what it's all about -- I like the Pass and Seymour outlets but YMMV.

I assume if you are worrying about outlet contacts, you've got at least 12 ga wire all the way to the breaker box, 12 ga power cords, etc.

The single most important thing you can do is check your building ground outside where the wires clamp onto the buried copper rod. If you don't already know exactly what I'm talking about pay an electrician to do it.

And without getting too exact on gauges, if the main house ground wire is smaller in dimeter than a pencil, consider replacing it -- a very low impedance path to ground solves many problems before they arise. Since the lugs above the main breaker are still hot even with the main breaker switched off, this is a job for an electrician.

As a general guideline, a 20A circuit for power amps, a 20A circuit for sub amps and another circuit for smaller equipment is a nice goal, adjust as needed for your equipment. If you are just running a mid size receiver and one sub amp, it's nice to give them all of a 20A circuit and put everything else on a second circuit.

[servicetech]

While on the topic of grounds be sure all A/V grounds are bonded together. Antenna/Cable/Sat grounds should be connected to the same ground as the power for your A/V system. Different ground potentials within the system can cause humming and lines to roll through the picture.

A quick way to check for common ground is measure the ground side of your cable/sat/antenna jack and see if there is continuity to the power ground.

[Dennis H]

As a general guideline, a 20A circuit for power amps, a 20A circuit for sub amps and another circuit for smaller equipment is a nice goal, adjust as needed for your equipment. If you are just running a mid size receiver and one sub amp, it's nice to give them all of a 20A circuit and put everything else on a second circuit.

If you're going to run separate circuits for an AV system, it's good to have them all on the same 120V leg of the 240V service panel. (Have an electrician do it if you don't know what that means.) In practice, most people can get by fine with a single dedicated 20A circuit.

[ThomasW]

Wiper contact area is what it's all about -- I like the Pass and Seymour outlets but YMMV.

They make good stuff, it's just not necessary to buy the hospital grade to get good outlets.

[Bent]

I'd think a decent Leviton could work

[Geoff Gunnell]

The Levitons are fine. Just for fun I went down to the basement and grabbed a boxed P&S CR20 and a boxed Leviton BR20 -- the wipers look almost identical, and plug insertion and removal feels almost identical. Thomas is absolutely correct about not needing a hospital (or industrial) grade outlet, and Dennis is right about making certain that all the outlets feeding interconnected equipment are wired to the same phase. Depending on how crowded your breaker box is, your electrician may have to move some other circuits to different breakers to do it.

The bonding of antenna/dish phone/cable and main grounds servicetech mentioned usually occurs at the clamp onto the buried ground rod, and I don't know how many of these I've seen these with the grounds wires loose, excessively corroded, or even entirely disconnected. If you dig it up to check on it, invest in a new rod clamp to either replace or add to the old one (one of the common problems is everyone trying stick their wire into one clamp, adding a second clamp and dividing the wires between them holds the wires much better). Refilling the hole with pea gravel will make your next check in a few years much easier

Periodically checking their building ground is one task that I feel many tool-using homeowners should be able to do themselves if they have a basic understanding of electricity. The risks are manageable: First, the risk of digging in the same area power, phone, and cable lines are buried -- hand dig with a trowel, slowly. Second, the risk if you have to briefly disconnect the main building ground wire from the ground rod -- I recommend shutting off the main breaker while you work on the building ground.

[Dryseals]

There are several types of "grounds." Your neutral, your safety ground and your shield ground. Sheild ground is the most misunderstood and may not even be required in your set up. Sheild ground is the one you would use if you ran shielded cables in your system

The first thing to determine is how old your house is and if the wiring is correct. All houses built now a days are required to have seperate neautral and safety grounds, the safety ground is the third prong on the plug.

The bigger question you need to answer before you get started is how each piece of equipment is internally wired before you get started. Many manufacturers tie the case (safety ground) and the neutral together internally. If they do this and you try to use your safety ground as a shield ground, then you've just set your self up for ground loop problems.

If you are in a house, go out and take a look at how your cable and phone come into the house, the phone and cable companies tend to "gound" their connections on the galvanized pipe of your feed to the house. Not a good "ground."

[chasw98]

I currently ( :B Joke alert!) use 4 20 amp circuits to power my installation. One circuit is dedicated to low level equipment with a Balanced Power Transformer to provide 2 legs of 60 volts each. In addition the remaining circuits have individual neutral return lines back to the main service feed. Code calls for 12 gauge so I used 10 gauge for all runs except ground which I used a 14 gauge. As Dennis mentioned all circuits are on the same phase in the panel and it is not the phase that the household appliances are on, i.e. refrigerator, dishwasher, etc.

Most of all, if you do not feel comfortable in doing this kind of work, GET A LICENSED ELECTRICIAN to help or do the project.

[servicetech]

The bigger question you need to answer before you get started is how each piece of equipment is internally wired before you get started. Many manufacturers tie the case (safety ground) and the neutral together internally. If they do this and you try to use your safety ground as a shield ground, then you've just set your self up for ground loop problems.

I've not seen neutral and cold ground internally connected on any video equipment, and don't see how they could do so and still meet UL approval. If the neutral leg in the wall socket/ac cord went bad then that would leave the case of the equipment at line voltage, not good. I'd like to see a schematic that shows this on something manufactured in the past 20yrs.

I've found on video equipment that their is typically 2 grounds "hot ground" and "cold ground". The hot ground is tied to the neutral of the power supply, cold ground is on the secondary isolated side of the internal power supply. If the equipment uses a 3 prong plug the ground leg is always connected to cold ground. "Cold ground" and signal ground are the same thing in most video equipment. I suspect audio gear is designed the same way.

Keeping all shield/safety grounds connected at the same potential will prevent AC/DC from traveling on the shields of AV cables. As you mentioned it's not uncommon to find issues near the ground rod with disconnected (or never wired !!) ground connections, especially in older homes. I've been on calls where I've been unhooked the cable TV line and got SHOCKED by the "ground". I've seen readings of 50V on the GROUND of a cable line, of course this is what promoted the call for me to go work on the video display..

[Geoff Gunnell]

Servicetech knows . . .

50V on the cable ground! I'm trying to visualize how that could happen -- I guess if that service connection was the only one following a booster amp and the grounding links had not been made correctly around the amp . . .

Anything like this should be reported to the untility involved immediately -- you don't want your house ground acting as a current dump for a utility subsystem, and a voltage that large indicates significantly incorrect installation at least, possibly accompanied by equipment malfunction. Make a big deal about it -- they need to get it fixed!

[servicetech]

Believe me I did. The customer called the cable company while I was in the house, they were sending a tech right out. I had to order a board for the set, and when I came back to fix the set the problem was corrected.

50V is an extreme case but I even see 3-10V more frequently than I like to. Normally the TV's ground path will drain the voltage to ground causing waves in the picture. Under 3V normally won't affect the picture, but I like to see 0V and pass a continuity test to the ground in the equipment outlet. With digital becoming more popular it's going to be interesting to see what effect low level voltages on the cable line have.

With no continuity from cable ground to earth ground you can imagine what this does to a TV when a surge hits. Lightning/power surge calls are about 1/2 on the power side and 1/2 on the signal side. Even if you don't have signal issues proper grounding will help protect your investment. Another thing that gets me is when a surge protector is used with a 3 prong to 2 prong adapter that effectively kills the ground and renders the surge protector ineffective. "But I bought the $150 surge protector, how did my set get hit?".

Incorrect HT installations done by the incompetent "professionals" really get me, but that's a topic for another forum.

[mpotoka]

Gol--I must be nuts... I am running 2 pro amps, my receiver, HD-A1, HTPC, BFD, and OTA receiver all through my 15A rated Power Conditioner. That is plugged into a 20A circuit, but even with everything running I have never come close to the 1650 watts that a 15A circuit gives you.

[Dryseals]

I've not seen neutral and cold ground internally connected on any video equipment, and don't see how they could do so and still meet UL approval. If the neutral leg in the wall socket/ac cord went bad then that would leave the case of the equipment at line voltage, not good. I'd like to see a schematic that shows this on something manufactured in the past 20yrs.

I've found on video equipment that their is typically 2 grounds "hot ground" and "cold ground". The hot ground is tied to the neutral of the power supply, cold ground is on the secondary isolated side of the internal power supply. If the equipment uses a 3 prong plug the ground leg is always connected to cold ground. "Cold ground" and signal ground are the same thing in most video equipment. I suspect audio gear is designed the same way.

Keeping all shield/safety grounds connected at the same potential will prevent AC/DC from traveling on the shields of AV cables. As you mentioned it's not uncommon to find issues near the ground rod with disconnected (or never wired !!) ground connections, especially in older homes. I've been on calls where I've been unhooked the cable TV line and got SHOCKED by the "ground". I've seen readings of 50V on the GROUND of a cable line, of course this is what promoted the call for me to go work on the video display..

Early morning post. My mind was picturing the many two prong setups from the past where as the neutral was tied to the case and the case set in wood. Not uncommon in the old days. Most of the gear now a days do not tie the neutral on the case for two prong units, but they do tie the case to the secondary side of the transformer ground, power supply ground. Three prong set ups do tie the case as a safety ground.

A lot passes in 32 years of doing this stuff and I've seen all kinds of grounding problems that can be traced back to the way a manufacturer ties their supplies down and then some one adds a ground for noise reduction and creates ground loops in the system. Mixing old gear and new gear can create these problems.