For a long time I've had a hum eminating from where the hydro connection braces to my house -- not at the meter at the ground floor, but at the top of the pole where the cables meet the house, on the wall outside a second floor bedroom. Sometimes it hums, sometimes it doesn't, but when it does, it resonates in the bedroom. On a few occasions over the years I've had both hydro workers and electricians at my house to troubleshoot, but they can't explain why this happens. They've changed the meter a few times, put some padding between where the cables connect to the house -- but nothing stops it.
I've also noticed that some electric appliances create a hum when turned on. For example, I have two identical small halogen lamps, both illuminating different areas of a desk. Both lamps are on the same circuit, but one hums and the other doesn't (even if the non-humming one is off). I might've thought that perhaps the humming lamp is defective, but I've noticed this same hum with some (not all) other electrical appliances in the house (e.g. I just bought a ventless electric fireplace for the master bedroom, and it's humming too). I don't know much about electrical. Could it be an overall grounding issue? Surely this isn't normal??? Any advice is much appreciated. Thanks.
I wouldn't worry about any of it. Where your service drop meets the house, any movement of those wires is going to cause a vibration that will resonate inside the house. It's quite possible that wind could set up a low frequency hum. I've heard an instance where a squirrel running on a service drop caused a sound like someone tapping the walls with a hammer.
As far as appliances go, some things just hum. Your ventless fireplace may have electric valves or small motors in it, both of which may hum in operation. Many devices with no moving parts, such as ballasts, transformers, and some light bulbs will hum because of the frequency of the electrical current flowing through them. The condition is actually called "60 cycle hum" and is harmless.
Is this normal? Yes and no. Dare I say it, you may be overly sensitive to the normal resonant sound of electrical devices. All electrical devices may, or may not create 60 Hz hum during operation, depending on who's listening... You are obviously not an electrician, and haven't dealt with the exact same question you are asking time and time again. A slight hum from a lamp, can sent some into a frenzy. Is it normal? Yes, and no depending on the degree, and how much money you would like to spend for some of the corrective measures. There are some, and everyone else but you will not be able to hear it possibly. Some hums are normal, some are not. All motors, lamps, transformers hum to a varying degree. Some electrical appliances emit noise as well. The average TV set can be heard by a dog for 100 yards in a state that a human would consider silent. Ultra-sonic motion sensors of certain Db levels are illegal in some states. For instance, I have neighbor down the road with motion sensors for his alarm system that make a dog whistle noise as you walk by, the person who lives there is totaly deaf to that frequency, thinks people are crazy when they tell himabout it.
I suggest you get a second opinion from someone (an electrician) who can actually hear it. As we could not quantify what is normal, or not.
Mark Heller "Well - I oughta....." -Jackie Gleason
Would there be a transformer on the same pole the other end of the drop is attached to? Under certain load conditions the "pole pig" could be humming loud enough to send the vibrations down the drop. And certain wind conditions would make the drop thrum like a guitar string as well.
I have a transformer right outside my bedroom window (about 15 feet away and same height) and I can hear it growl on occasion.
The humming desk lamp probably has a loosely mounted transformer, not a big deal unless it also overheats.
And the fireplace, I have heard heating elements of both open nichrome and glass-covered coils hum or buzz.
Unless the hums are accompanied with severely dimming (or flaring bright)lights in the house I wouldn't consider it to be of any concern.
edited for spellin's
[This message has been edited by mxslick (edited 11-11-2005).]
John, I'm glad to know that this is common and not a safety issue.
e57, if I am sensitive to such noise, my wife and sons are too, 'cause they can hear it also.
mxslick, the transformer sits at the top of a hydro pole about 80' ft. from my house. I find it funny that you mention "...make the drop thrum like a guitar string as well", because the bedroom outside of which the hydro connects to the house at the second floor, I'm now converting to a small home recording studio. I didn't mention it in my initial post, but you may imagine that this hum will be bothersome if it happens while I'm recording -- mics are very sensitive.
Anyhow guys, I plan to have some electrical work done soon, and as I said, although I've posed the issue to electricians who came to my house before, I'll raise it again.
Electrical hum is caused by magneto-striction. This is caused by the iron molecule in the core of the device being stretched one way by the magnetic field, then reversed as the AC current (at 60 hertz) reverses the polarity of the magnetic field. How much you hear depends on the strength of the magnetic field and how well the core of the device is clamped.
(Of course, the smart ass reason a transformer hums is it doesn't know the words)