Dimmers' detrimental effect on sound quality

Dimmers may potentially introduce some noise. But if you do not hear it, then no need to worry. They won't affect sound in any other way. Just make sure you get high quality dimmers, not the cheapest ones.

If I understand correctly, you have separate circuits for lighting?

Shouldn't be a problem. Any good-quality dimmers are very unlikely to cause any noise, and since you have separate circuits it's even less likely.

I wouldn't worry about it, if there are any problems you would hear them immediately. More likely you'll hear buzz from the filament in the bulbs themselves, if anything. I never hear noise problems in audio circuits from dimmers anymore, it's not even really a concern IMO.

Lutron brand dimmers are the best for home installs. They have rotary and slide dimmers with a soft on to save bulb life and provide a no flash illumination.

Circuit breakers don't provide any isolation, until they trip. All circuits are in parallel.

If you don't hear any buzzing then you're all set. But solid state SCR dimmers also radiate RFI into the air, and down the wires back to the electrical box, so just having your lighting on a separate wire doesn't guarantee anything.

--Ethan

Not if they're on different legs...

how do you isolate the breakers then?

Im adding more circuits to my HT room soon so Im wondering if there are some products I might want to buy.

YOu don't...what are you trying to achieve?

I absolutely agree with Mr. Winer's comment. Many dimmer circuits, as well as 120v to 12v transformer circuits in MR16 style halogen lighting can create huge amounts of radio frequency interference. My sensitive amateur radio gear goes "nuts" with high levels of injected RFI noise when the track lighting in my kitchen, or a specific dimmer on lights in the dining room (hopefully soon to be replaced !) are in use.

I'm also constantly amazed how may electricians will mix lighting circuits with receptacle outlets to save a few feet of Romex. Rarely are residential lighting circuits 100% on separate circuits and breakers.

Can anyone comment specifically on the use of ELV dimmers? I've read that they significantly reduce RFI and may safely be used in an A/V environment.

Penn,

Typically, one doesn't address power quality, unless there seems to be a specific issue. However, balanced power systems are very common in broadcast and studio environments, and they provide the best power platform from which to build a low noise A/V system.

The two terminals on each circuit of a balanced system, have voltage that's 180 degrees out of phase with each other, and the system ground is sourced from the center tap of the Iso transformer. So then there is never any voltage present, or any current flow on the ground and all your shields are referenced together.

It's just like low level balanced interconnects, it uses common mode cancellation to take care of the noise. All the garbage that's generally on the lines, sum to zero.

It's a relatively easy diy, but many turnkey systems are available too. There's even small tail panels available, ideally suited for a build out like you're doing. In addition to single circuit types, there are 6, and 10 circuit versions.

The only caveat with isolation transformers, is current limiting for high draw devices. I'd consult with the different mfrs. if you're interested.


Good luck

All the legs come together at the service entrance, so they're in parallel.

Oh, maybe you mean the two 120V legs.

Which are connected to opposite ends of the same transformer secondary.

I looked into them.... the one I saw was very heavy, maybe over 200 lbs?

I don't remember the size I was looking at. I'm wired for four 20 amp circuits so I might have been looking at an 80 amp? Been too long... I just know I saw the price and weight and kept moving on.

When (if ever) my basement is finished, if I have any issues that a balanced transformer could fix, I can easily add it later given how I wired things. Right now, I decided that I wasn't going to fix a problem that I don't know exists.

Exactly why I made it a point to insist on separate light/receptacle outlet circuits when we did out HT remodel several years ago .. additional cost was minor ..

Some electricians wire lighting circuits correctly, some don't. The correct way is: The Hot, Neutral and Safety Ground wires should be in close proximity to each other from the breaker box to the switch to the luminary.

Why would taking the neutral down to the switch box be correct? Are you referring to some form of noise immunity?

The following page started on the wiring problem, then moved to other tests.

http://www.synaudcon.com/site/author...-introduction/

NEC requires all conductors in a given circuit be in the same jacket/conduit so that there is no half of the circuit in a cable or conduit. The neutral is joined in the J-box housing the dimmer and then exits in the same cable as the hot to the light fixture.

It is to avoid induction heating. If the hot and the neutral are in the same cable, their fields cancel each other out.

The only reason one on take the neutral to the switch is if the device requires a neutral. Typically, one would take the hot down, and the switched leg back up to the fixture. Now, if the device needs a neutral, as some timers/dimmers require for operation, then one would take a neutral to the device.

Some newer dimmers can be retro-fitted into a two-wire typical switch drop, whereby the return is converted to a neutral, and one mounts a corresponding piece up at the fixture. The two pieces communicate for controlling dimming values. I've never used them, so I don't know about their longevity etc.

Regardless, in a switch application, as far as I know the neutral is there only for a difference of potential, not to counteract magnetic heating as it is generally used in other applications.


Thanks

In a switch loop, if the hot and the switched hot are in the same cable, the fields cancel out, too, since equal current is flowing in opposite direction. Even without a neutral.

Current code requires the feed -hot and neutral- to go to the switch enclosure and then after the switch, to the load. Sorry.

Citation?

I don't have a 2008 code book. Has it changed since 2005?

Lots of switches were certainly wired that way in the past. My house, which was built in 1964, has the neutral going to all the switches. And that is that standard way of doing it where I live today. Makes it handy when retrofitting switches with electronics that require the neutral.

The effect on induction heating is probably not significant in a typical residential lighting circuit. It sure seems like the fields in the two hot wires in the cable would cancel out. But that is NFPA's reasoning, for wiring in general, not specifically switch wiring, as I understand it.

I think Gizmo is referring to 300-3(b), at least that seems to be it in my even older edition. It does say "grounded conductor...where used". I guess one could argue with that, but to me it means if the grounded conductor is anywhere in the circuit, it has to be everywhere in the circuit. There is no exception for a switch in the edition I have. Gizmo might be referring to something else that I am not aware of.

Grounded conductor (neutral) is not just a voltage reference. It carries full current in a normal branch circuit. In a multi-wire branch circuit, it may carry less, even close to zero, if the load is evenly balanced between the two hots.

In any case, the cost difference between wiring a switch with and without neutral usually isn't much...

Interesting discussion, as I've not opened a code book in some time. Lets clarify some things; The standard of only taking the hot and switched leg down to the switch doesn't only date back to the '64 era. If there's been change in this regard, it's a relatively new change. Also, if there's been a change made I wish one of you claiming this would provide a link to it. There are standard practices that vary around the country, that why the NEC is the ultimate reference. The NEC is a minimum however. Additionally, in my experience, I didn't think the NEC made changes to enable things handy for retro-fitting. Dimming has been around for decades and I'm not sure it's any more more prevalent now than it's been in years past.


Regardless of significance, parasitic magnetic heating is never allowed in any situation I know of.


I'm intimately aware of the function of each conductor, neutral or otherwise. I've never heard of taking the neutral to the switch, unless the switch needed the neutral for a difference of potential.


I'm not so sure about this. It's entirely different when a third insulated wire needs to be taken to the switch. I have zero residential experience, however I do know that in that non-conduit environment, 12/2 w/ground is abundant. Most likely 95% of what is purchased and used is 12/2 w ground,...either Romex or maybe even MC. There are some jurisdictions that require conduit for residential, but for this discussion, insignificant.

Anyway, to get a more expensive 12/3 w/ground, changes everything. If conduit and THHN were being used, it would be relatively insignificant. However with 12/2 w/ground, one feeds the switch with the white, the return switch leg is the black, and the neutral is kept up in the fixture JB. As far as I know, this was the standard in the 60s, 70s, 80s, and 90s. If this has changed, and the neutral shall be required in the switch box,...whether the device needs it or not,..it is news to me. I do not follow code changes, and if this is the case, please link to further information.

There are a few instances when the NEC makes provisions to "make it easier on the next guy", and that's entirely possible here, but it's not likely for reduction of parasitic magnetic heating.

Thanks, good discussion.

When using NM-B (Romex) around here they usually just daisy chain a 12-2 w/ground to each j-box with a receptacle or switch, and run another 12-2 w/ground back up to the switched device. They connect the neutrals with a wire nut. Didn't mean to imply that this kind of wiring is required by the NEC to make things easier, just that it does make things easier for retrofits. NEC is all about safety.

Interesting. I just found an example of a switch loop for a circuit fed at the light that doesn't take neutral to the switch in my old copy of Electrical Wiring Residential. And it is not called out as a code violation. Nothing explicitly in Article 380 Switches in my old copy of the NEC one way or the other about it. Only thing I can find is 300-3(b) as mentioned above.

Found a snippet in an article by Mike Holt here that says a neutral isn't required in a switch loop. And he has a pretty good reputation as far as NEC goes. OTOH the ultimate authority is the authority having jurisdiction (AHJ), and it seems that a lot of AHJs interpret the NEC as requiring the neutral.

Looks like it will be a requirement in the future, with exceptions, to accommodate electronic switches that require the neutral no less. Read this.