Exterior HID hums loudly when switch added

[BigEdgar]

Hi,

We have a family cabin with a detached garage, and this detached garage has a bright HID light out front. We use it in the winter time to light the driveway for sledding (should be an olympic sport

When we bought this place, the HID was only able to be turned on via flipping the breaker on the panel (there was a dedicated circuit for this HID light). This was silly, so we added a switch at the end of the run so we could switch it on and off. However, when we flipped the new switch, there was a very loud humming noise. Not the kind of background hum you get from fluorescent bulbs, but a really loud and rather scary hum. We didn't like the sound of it, so we flipped the breaker off again. FWIW, before we added the switch, the HID did not hum when we turned it on at the breaker.

My brother and law and I did the work, and while I'm just a weekend hack when it comes to wiring up electrical, my brother and law is a contractor for a high end home remodel company, and he knows what he's doing. Not saying we haven't screwed something up, but just letting people know we're not complete nincompoops when it comes to wiring.

We went back and checked our work and everything was wired properly. We properly wired up the switch at the end of the run, and it's a 15A switch which should be fine for the load.

We don't know much about HIDs, so I figured I'd see if anyone on this forum had any thoughts. Any ideas on what might be going on here?

Thanks for any thoughts.

[Billy_Bob]

There is a thing called a "ballast" sort of like fluorescent lights have.

You may have installed the switch between the ballast and the light bulb? The switch would need to be before the ballast of course.

And these have a power on sequence - designed to be turned on and left on, not on/off. Might try leaving it off for about 20 minutes, then back on. They need to cool down before switching back on.

This power on sequence you can see with street lights or parking lot lights. At first they start dim, then get brighter.

[BigEdgar]

Thanks for the thoughts, Billy Bob. We traced the wiring as far as we could back to the panel and eventually lost it in the wall, but there was no separate ballast on the 50 feet of wiring that we could trace.

We'll be up there next week, so we'll try starting it cold and see what happens. Appreciate the suggestions!

[rayh78]

Did you even touch the light fixture?
When I have had this on HID lights its the transformer/ballast thats screwed to the light housing. And the screws are a little loose causeing it to vibrate.

[drick]

Yeah if you touched the fixture my money is on a loose screw or you reasembeled it incorrectly. Some HID ballasts vibrate more than others. Tighten up everything. Its most likely a hardware issue, not a wiring one.

-rick

[BigEdgar]

We never even touched the fixture, it just stayed installed while we worked with the wiring that was fed into the garage. Thanks for the ideas.

[burleymike]

Try bypassing the switch and see if the hum is gone. What type of HID fixture is it HPS, MV, MH, CFL? How many volts/watts is the fixture rated for?

[jadnashua]

Is the switch anything other than a simple on/off (i.e., is it electronic or a timer)? Does the switch have an indicator light on it? A simple wall switch should not have changed the way it operates unless it is defective. What is the rating of the switch and the load it is feeding? WHen it is operating, try measuring a/c volts across the two poles of the switch. It should be very close to zero. If it isn't, the switch resistance is high, and may be dropping the voltage to the lamp. Find a better switch, if that's the case. Not all switches are created equal...you might try an industrial rated one. They tend to have better internals than the run-of-the-mill ones.

[BigEdgar]

Is it Occam's Razor that says the simplest explanation is usually the correct one?

Well, in this case that's true. Turned out to be a bad bulb, and it happened to go bad just as we installed the switch. It's a metal halide fixture, so we just got a new bulb for it, and now it's working like a charm.

Thanks for all the ideas - you all helped us rule out a bunch of possible reasons for this going bad and helped lead us to the right one.

[Billy_Bob]

I hate it when that happens! Very difficult to troubleshoot the problem because you think it is something you did!