Circuit breaker humming?

[Ken Platt]

Folks -

After adding another grow light to my spring planting seedling setup, which runs off my shop sub-panel on a 15 amp breaker, I noticed the breaker was making a humming sound. There is nothing on the circuit besides the three lights, which total 860 watts/8 amps according to their labels. If it matters, the lights are Agrobrite T5 high-output fixtures, and are new-ish (2 bought last year, the third just a few days ago).

I tried two other 15 amp circuits in the same subpanel, also with nothing else being powered at that time, and they both immediately started humming. I plugged the lights into a 20 amp circuit, also on that same subpanel,and no hum.

In the interests of experimentation, I grabbed a 1500 watt space heater and plugged it into the same 15 amp circuits, and there was the tiniest, barely audible hum. I'd never have noticed it if I wasn't putting my ear to the subpanel and having absolute quiet around me. The hum when they lights were plugged in was much louder, easily heard even at a distance.

Oh, and there was virtually nothing else running off the subpanel during this time - just a couple overhead fluorescents. THe subpanel is 30 amps,I

Can anyone shed some light on this? Are all of the 15 amp breakers bad, or getting there? Is this just electrical noise? Why do the lights make so much hum even though they are well within the circuit's capacity, and make MORE noise by far than something taking almost 2x as much power? I would love to measure the current directly, but I don't have an ammeter.

And, most important of all, is it ok to run those lights on the 15 amp circuit? The 20 amp circuits run my shop machines, usually, although I can swap where things plug in when I'm working in the shop. Kind of a PITA though.

Thanks for taking the time to read this -

Ken

[John RStegall]

I am not an electrician but I have switched out defective circuit breakers. I switched the 15 amp for a 20 amp. I turned off the entire panel, checked it with my voltmeter, then removed that cover over the breakers, loosened the screws holding the wires in. Then I removed the old breaker (which was badly corroded) and installed the new one. I am not recommending you do this but I would consider having it swapped out. That should solve your problem and make life a little less frustrating.

[George Bokros]

I am not an electrician but I have switched out defective circuit breakers. I switched the 15 amp for a 20 amp.

To me this seems questionable. I have been told the amp rating of the breaker is determined by the ga of the wire from the breaker to the outlets and switches. As I understand it 15 amp breaker for 14 ga wire and 20 amp breaker is for 12 ga wire.

[Wade Lippman]

To me this seems questionable. I have been told the amp rating of the breaker is determined by the ga of the wire from the breaker to the outlets and switches. As I understand it 15 amp breaker for 14 ga wire and 20 amp breaker is for 12 ga wire.

Hopefully he made certain that he had 12 gauge before he made the change. Some electricians use 12 gauge for everything because it is easier than having two sizes. I am not sure why they don't then use 20a breakers.

Anyhow, if you tried your lights on three circuits and got hum on all three AND nothing else hums on those circuits, i don't think changing the breaker will help any. Sadly, i don't know what will.

[Bruce Wrenn]

Hopefully he made certain that he had 12 gauge before he made the change. Some electricians use 12 gauge for everything because it is easier than having two sizes. I am not sure why they don't then use 20a breakers.

Some devices (bath room fans as an example) are required to be on a 15 amp circuit by manufacturer. damhik!

[Mike Gresham]

Some devices (bath room fans as an example) are required to be on a 15 amp circuit by manufacturer. damhik!

That is interesting information Bruce. Did they say why? I hope they don't expect the breaker to protect the fan.

[Ken Platt]

I don't have any problem swapping out a breaker - I haven't done it before but it looks pretty simple, and since this is a subpanel, it's easy to switch all the power off. But, it seems like I am getting that same humming from at least 3 different 15A breakers.

I was at the local Ace today, so I grabbed a breaker - $9 or so (they had cheaper, but those unpackaged electrical components always seem a bit sketchy to me). I might try it just to see.

George, my understanding of breaker amperage is the same as yours. I am not sure what the wire gauge is in a lot of my home lines as it's BX, so nothing written on the outside like on the romex stuff. I'd be afraid to go up in amperage.

Ken

[George Bokros]

George, my understanding of breaker amperage is the same as yours. I am not sure what the wire gauge is in a lot of my home lines as it's BX, so nothing written on the outside like on the romex stuff. I'd be afraid to go up in amperage.

Ken

You should be able to tell with a wire stripper. The notch that strips the wire insulation off would tell the gauge. Start with 14 ga and if it does not remove the insulation then try 12 ga. The gauge that removes the insulation is likely a good judge of the wire gauge.

[Brian Elfert]

I was at the local Ace today, so I grabbed a breaker - $9 or so (they had cheaper, but those unpackaged electrical components always seem a bit sketchy to me). I might try it just to see.

Most brand name circuit breakers are generally sold without packaging unless they are expensive AFCI or GFCI breakers. You likely paid more for a breaker repackaged by a third party.

[John K Jordan]

That sounds odd to me too. You can get an inexpensive clamp-type amp meter at Home Depot or an electrical supply house. I clamp one around the hot wire right at the breaker to check the total load I'm applying on that circuit in the winter with livestock and poultry water heaters.

BTW, I use T5 HO fixtures in my shop with no humming at the breakers, but they are not the Agrobrite. The T5 fixtures I have use electronic ballasts. Maybe the ballast is acting odd. If it just started this when you added the third light, maybe that one is suspect. Maybe try running the bulb in a different fixture?

Is the hum 60 cycle or a higher frequency? I'd personally check the lines with an oscilloscope to see if the fixtures were putting something back on the power lines, but not everyone has one. Maybe an electronics geek friend could take a look?

JKJ

[Rod Sheridan]

It sounds like harmonics from the electronic ballasts are causing a component in the breaker to vibrate.

Do you have any information on the lighting fixture? I would be interested in seeing what the THD (Total Harmonic Distortion) is for the ballast.

Regards, Rod.

[Ken Platt]

Thanks all for the replies. I feel a bit better that I'm not the only one who can't figure this out. Although, the replies sure sounded a lot smarter than me.

I fiddled around with the things today, and found that I still got the hum with only one of the 3 amp lights going (One of the lights is 4 bulbs/2 amps, the other two are, each, 6 bulbs/3 amps) The hum was softer, though. It steadily gets louder as I turn on the other fixtures.

Rod, https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 this is the fixture. I can't find any details about the ballast.

John, I don't have any friends with oscilloscopes, but Harbor Freight has ammeters for around $15. I have read threads in which folks claim good experiences with their multimeters, so perhaps this can give me some idea what the actual current draw is on these fixtures.

For now, since there doesn't seem to be any apparent problem when I run the things on a 20a circuit (which is in the same subpanel box as all the 15a ones that buzz) I guess I'll just leave set up that way. It's a minor PITA since I have to move the fixtures to a DIFFERENT 20a receptacle to run my shop machines, but as soon as the weather stabilizes - looks like about another week - I will be able to get my seedlings outside and won't need so many lights. I've got several trays of lettuces, broccoli, cabbages all ready to move out as soon as I can get the ground turned over and the plastic tunnel set up.

Thanks again folks. I'll post when I check the actual current when I get that ammeter this weekend.

Ken

[Mike Budzynski]

There is a possibility the breaker is going bad but since it seemed to follow the to the other breaker I would rule that out. DO NOT swap a 15 amp for a 20 amp breaker unless you can absolutely verify that you have 12 AWG wire and not 14 AWG wire that may have been installed with the 15 amp breaker. You run the risk of a fire if you do. If you have romex - by code all electrical distribution conductors must be marked on the jacket.

The possibility here is that the current draw is actually more than is listed and the breaker is on the threshold of tripping. If you have access to a clamp on amp meter - this will tell you immediately. If you do not - it is cheap enough (cheaper than a fire) to get an electrician out and look at it.

Out of curiosity - is this a residential site or is this possibly a commercial connection where 3 phase power is available?

[Roger Feeley]

We just built a new house and the electrician put in Square D QO breakers. These are commercial grade breakers. Square-D offers a residential grade (homeline) but the electrician claims that they make buzzing noises.

My point is that maybe buzzing noises are normal for certain types of breakers?

FYI, QO stands for Quick Open. I guess they trip faster.

[Matt Schroeder]

If the three lights plug in individually I would try them all separately and see if one of the fixtures alone causes the problem (start with the new one). If none of them do it alone then I would try combinations of two (A&B, A&C, B&C) and see if the higher draw causes it--trying to identify if one fixture seems to be the problem. If it turns out to be the new one it may be wise to exchange it if possible. At least this might help narrow down something about the problem. It does seem odd that the heater doesn't cause the sound although it is drawing more current--unless there is something about the middle of the range that hits a resonance? This part gets fuzzy for me.

Matt