Radio interference , lighting

Question

I recently purchased a new place to me. We have a large horse barn that we pipe FM music to the horses. Last weekend I was in the shop attached to the arena and stalls after dark turned the shop lights on and heard total static on the speakers (they were turned up for the 4th fireworks) all 3 circuits in the shop have 3-4 2 tube 4' T 8 fixtures. I did turn them all off and then each one on. All 3 circuits created the problem. I checked the ground to neutral voltage and it is .129v there is a local ground rod as this is a sub from the house, the ground buss is isolated from the neutral and I tightened everything in hopes it was a bad connection no change. Mid week I added a RFI Filter to the panel. The noise is still there on all 3 circuits, no problems with the 2 HID arena light circuits. Tried a high end Kenwood receiver and amp and still have the noise, not 60hz more like static. Has any one run into this problem and have a fix? There are step up transformers going to the speakers and then step down that kills our neighbors ham radio. But have never run into a problem quite like this. Today I checked both TAC rooms and the isle lights all fluorescent also but no noise on those all fed from the same panel. Update, last night I checked several of the fixtures to verify the ballast they were residential class b not commercial. Maybe tonight I will move the breakers all to L1 then L2 to see if this makes a difference unless any one has a better idea. I did change the circuits to L1 still have the problem. Moved all 3 to L2 noise still there. Tonight I checked the middle and 3rd level lights to double check grounds and voltage from ground to neutral, I did change 2 of the lamps on 1 fixture as the ends were getting a bit dark, still no change all 3 of the circuits still cause the noise, All 6 of the ballast are class B. Only 3 more fixtures to check but will have to wait until tomorrow as I have to put a ladder in our tractor and have the Wife lift me up... I hate doing this and am open to other options. Any Ideas?

Answer 1

Thanks for the suggestions, I finally figured it out. This is a new one for me. Several lamps on the top fixtures were loose (still working fine but loose). When I opened the fixtures to check the grounds the noise reduced by the time I got to the last one the noise was gone. My wife thinks when we loaded the hay loft in June we must have shaken them loose. The loft is on the other side of the wall. I have never run into this in the past so it can be something to look for once all the lamps were reseated in the fixtures the "static noise" is totally gone. No other problems found. I did check the ground rod with a clamp and the ground was a solid 2.4 ohms.

Answer 2

The ground-neutral voltage is no big deal. You ought to have some voltage difference if there's any load on the circuit.

I would start by eliminating radio jamming. Get a battery powered, portable radio - a car or truck will suffice. Do you get the same interference? If so, the problem is radio (RFI). AC power line conditioning will do nothing. Most likely it's duff ballasts, I would be curious about the brand of ballast. Otherwise...

If the panel filter does nothing, that suggests the fox is in with the chickens, i.e. on the same side of the filter. If possible, move the filter so the lights and stereo are on opposite sides of the filter.

To a certain extent, fluorescent ballasts are noisy by nature since they are driving a high frequency signal (2k-50kHz) to the unshielded lampholders and bulbs. But they may also make unnecessary RFI or line noise. GE makes ballasts of superlative quality for about 30% over their top tier competitors. If the lights are the issue, try one and see if that corrects it.

Another option is to go LED, but they too have switching power supplies so beware of quality issues. They are inherently DC and do not radiate high frequency AC anywhere beyond their power supply circuit, which is easily shielded if the manufacturer chooses to.

Answer 3

Put a screen over/around the lights... this is called a faraday cage. By putting a farady cage over the lights, you will block the interferance emitted from the ballast (or anything else).

You should read about them... but here's a video: The Difference Between Grounded and Ungrounded Faraday Cages Regarding AM, FM & 2.4 GHz WiFi (microwaves)

In this video, the guy uses chicken wire. Chicken wire is not as good as tighter meshed screens, but it might work okay for your lights.

And here's another video just for fun (informational purposes): Faraday Cage