It's probably a pi network, or maybe a ladder network. Basically, it's a low-pass filter intended either to keep RF that's on the power line out of the load, or to keep the load from putting RF into the power line. Or possibly both. (The filter works in both directions, but RF of concern is probably just coming from one direction.)

Edited to add: "EMI" means "Electromagnetic Interference."

[This message has been edited by SolarPowered (edited 03-27-2006).]

I have seen many of these over the years, but always inside of equipment. Hash filters like these usually appear like transformers mounted sideways on schematics. They often include them with input plug and fusing assemblies.
Joe

Just a guess, but is there any power line communication devices in the home? Like a "wireless" switch arrangement X-10, or the like?

Is that thing at least mounted INSIDE of a panel or enclosure of some kind?

Anyway, here's a typical schematic or what's inside one of those things:





[This message has been edited by NJwirenut (edited 03-27-2006).]

I shot the picture a little too close. It is inside a box. The picture is with the cover removed & a nipple attaches it to the panel.

Dave

PS If I'm following you right this is going to some equiptment, so I guess I'll be tracing the wiring.

Would most likely be used to feed either sensitive electronics (computer, home theater, etc.), or something that would produce large amounts of RF interference (furnace ignition transformer, ham radio gear, etc.).

NJ Wirenut - I'm not to savvy on EMI filters. Are you saying at the load end, you can connect either something you're protecting, or something you need protection from (something transmitting EMI)? Or are their different filters for sensitive equipment vs. EMI Producing equipment

The filter will work either way. It is essentially a lowpass filter, which allows the 60 Hz to pass right through, but shunts high frequency noise to ground. The shunt capacitors present a high impedance at powerline frequencies, but look like a short at RF. The series inductors are just the opposite, having very low impedance at 60 Hz, but effectively "choking" high frequencies from passing through. There are different types of filters made, which are each optimized for use either at a noise source or at the sensitive equipment, but generally this type of packaged filter works pretty well in either application in my experience.

If used to prevent a noisy device from junking up the powerline, it would be best to locate the filter as close as possible to the noise source, so as to reduce the length of "dirty" feeder cable which will radiate the noise like an antenna.

[This message has been edited by NJwirenut (edited 03-28-2006).]

Regardless of what it is and what it's supposed to do it doesn't belong there. Obviously a DIY or maybe an EE installation. It's "home brew" and not listed so not allowed. Any inspector worth his salt will red tag it.

-Hal

[This message has been edited by hbiss (edited 03-28-2006).]

It isn't "homebrew", except for the enclosure.

The filter itself is a commercially available, UL/CSA recognized component intended for use on these voltages (120/240), and up to 30A current.

I fail to see any violation here, with the possible exception of wire bending space inside the enclosure.

No more objectionable than mounting a contactor or other properly rated device inside your own enclosure.

Exactly what NEC violation should an inspector red tag this for? Not understanding what something does or why it was installed is not sufficient reason for an inspector to issue a violation.


[This message has been edited by NJwirenut (edited 03-28-2006).]

I traced the wire today & it is for a computer outlet. The owner is a programmer, so I suspect he had it installed. As I mentioned previously, there is a cover for this box, I took it off for the picture. The only violation I noticed in the installation was the use of NM wiring not allowed here, and wrong color wire used.

Thanks to all for your input. Would this be considered an installation for power quality?

Dave

Yep.

If you plan on reinstalling this unit, I would suggest a somewhat larger box, as well as a ground wire run from the ground stud on the filter (between the 2 line terminals) to the ground bus in the panel.

Does the owner realize that this thing offers little to nothing in the way of transient voltage suppression? Maybe you should try to sell a "whole house" TVSS unit along with the service upgrade since the owner seems concerned about power quality...

[This message has been edited by NJwirenut (edited 03-28-2006).]

Thanks for the tip. I am installing a whole house surge suppressor with this upgrade.

Dave

What most people do not realize is the line filter on a switched mode power supply for a computer is there to protect the rest of the world from computer generated noise, not to protect the computer.
The same was true of all of that bonding you saw in the raised floor computer centers.
It was the computer that made all the ugly "noise" we were protecting against.

Yes, most likely the computer plugged into the output of this thing already incorporates a similar filter network in it's power supply input wiring.

And to touch on something mentioned earlier, if there is an X-10 or similar wireless control system in use, it will NOT function properly on that branch circuit. That filter will remove the control signals quite effectively.

I doubt that it really matters here, but I could see where this installation that Dave has encountered might actually result in increased radiation. If Dave was dealing with Romex and noise was coming out of the computer PS input, the wiring between the filter and the computer outlet might have better antenna characteristics with the filter on the far end.
Joe