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.

[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

[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

[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.

[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.

[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

[Tom Stenzel]

It's possible that the T5 ballasts have a high peak current even if the average current is lower. That is the ballast draws current only for a short portion of an AC cycle and is zero for most of the cycle. That could make a breaker buzz. Even if you installed the same model 20 amp breaker AS A TEST it'll do the same thing if that's the case.

I tried looking up info on this using Mr. Google but results for the peak inrush on startup for electronic ballasts pushed anything useful out of the way.

If I were to make a project out of it I would put a low resistance in line with the load and put a oscilloscope across the resistor. I did things like that at work when we had to reverse engineer the ratings of some parts in a 200 hp VFD. But there I had the equipment to protect us from 480 VAC, at home I ain't got nuthin'.

Oh, and when I opened up the breaker panel on my INSPECTED* house I found a 14 gauge wire attached to a 20 amp breaker. The same panel where they had forgot to tighten the incoming feed from the meter. I still wonder how come the house isn't a pile of ashes.

*The inspector didn't find this. Or any of the other problems in the house. I could make a remark about what that numbskull couldn't find but the mods wouldn't like it.

-Tom

[Kev Williams]

I somewhat understand home CB's, and found this simple explanation and drawing online...
cb.jpg

--in just looking at this drawing and the parts involved, I now know why my breakers sometimes 'sizzle' when my 80 gallon air compressor or my big HF dust collection blower kick on- the points are momentarily bouncing...

It also apparent, to me anyway, that a constant stiff draw could cause the points and/or the mechanical parts within the breaker to vibrate at 60hz, turning the breaker into a miniature speaker... which would hum

[Wade Lippman]

Oh, and when I opened up the breaker panel on my INSPECTED* house I found a 14 gauge wire attached to a 20 amp breaker. The same panel where they had forgot to tighten the incoming feed from the meter. I still wonder how come the house isn't a pile of ashes.

*The inspector didn't find this. Or any of the other problems in the house. I could make a remark about what that numbskull couldn't find but the mods wouldn't like it.

-Tom

Code is extremely conservative. There is little chance of 14 gauge causing a problem with a 20a breaker. My 23a water heater was on 12 gauge wire and it didn't have a problem in the 22 years I owned it. And you couldn't find a worse case than a water heater; it is full current for long periods of time. The loose connection is a more serious problem; but even there, an arc insist a proper box shouldn't burn your house down.
Obviously you want to follow code because you never know when that one chance in a hundred is going to happen, but generally it is overkill.

After i bought my house I was shocked to find the water heater and furnace installations were way way out of code. The Town inspector said that he can't know all the requirements for every system and generally relies on the compentency of the contractor.

[John K Jordan]

Code is extremely conservative. There is little chance of 14 gauge causing a problem with a 20a breaker.

My favorite story is from working on the wiring in a children's summer camp in the central highlands of Mexico. Someone had wired up a water heater with over 100 feet of 14ga Romex connected to a 50 amp breaker. There were no supplies within a 10 hour drive so I had to wait until the next year to bring wire and a breaker to fix it. Fortunately the building was still standing.

JKJ