[ZinscoMan]

This circuit has several wall outlets all on a 20amp standard thermal breaker. Most are never used (behind furniture).


To setup the question, these are the five consecutive wall outlets along the circuit to note:
Outlet #1: TV (rear projection analog), VCR on surge suppressor (it's not even close to the limit on amps)
Outlet #2: Normally nothing, currently Christmas tree lights on extension cord (3 strands, 50 tiny non-blinking on each strand plugged into different outlets on extension cord)
Outlet #3: Normally nothing
Outlet #4: Lamp with 100W bulb
Outlet #5: Normally nothing


I noticed when walking within 5 feet of outlet #3 a steady buzzing noise and putting my ear to the outlet it got louder so it is the source of the sound. Nothing's plugged into it. At the time, I had the lamp lit on #4, the TV was running on #1, and the Christmas lights were lit on #2. Checking the sound occasionally, it neither got lower in volume, changed in tone, or got louder after a few hours. The wall plate was not warm to touch. I listened to all the other outlets--only #5 had a much lower volume buzzing (with nothing plugged into it).


So I began a process of elimination. Since I haven't noticed it before, I suspected the seasonal Christmas lights could somehow be the cause even though that's not their outlet. Whether with only #4 (lamp), #2 (tree lights), or other combinations running, it was when #1 (TV) was running that I could hear a much lower volume buzz on #3 only when putting my ear near the wall plate (no buzz this time on #5).


So I got out my multimeter and started inserting the leads into each of these five wall outlets. In each one, I got a steady 122 volts. Then I checked the other unused outlets on the same circuit (just 3 additional). They all checked out with 122 volts. None of them warm to the touch.


So then at the same time of the evening I turn on the same things drawing the same amount of power as when I first heard the buzzing--no buzzing this time. Not even low hum coming from outlet #3 (and no buzz on any of the others). So while initially I was suspecting a loose connection but ruled it out since the outlet sees very light use and anything when plugged into it fits snugly and isn't difficult to pull out the plug... now I don't know what happened. Harmonics? 27 degrees F outside? Since it's not reproducible I'm thinking maybe it's not serious. Any ideas on what it was and what I should check first that I haven't if it comes back?


Thanks for reading,
Morty

[donf]

You need to pull that receptacle and tighten the screws holding the wires. The buzzing you hear is arching. This is a condition that will cause a fire if not fixed as soon as possible.

[talaniman]

In addition there is a possibility that the house wiring is frayed, deteriorated, or damaged, so I recommend a visual inspection of the wiring. You never know what, or how receptacles are connected, or affect each other when they are. Do you have door bells, or dimmer switches in your home? If Don's suggestion doesn't solve your problem then you must broaden your search for that problem.

I hope it is just a loose wire or connection, but if not please let us know. Tracing wires that may be years, or decades old, is a complete P-I-T-A at best and you never know what kind of short cuts were taken by a DIY'er.

[ma0641]

I have seen a similar thing with back fed outlets. Even though you may have little on it now, at a previous time someone may have loaded the power and since the power goes through the outlet in use or not, it overheated the wiring. What you may be hearing is electrical arcing. Pull the noisy outlet and look at the wiring attachment. If the outlet is back wired or you see discolored wiring,have someone replace the outlet and put the wiring under a screw. Good luck, don't wait.

[ZinscoMan]

No dimmer switches in the whole house. I've lived here from the beginning so I know there's never been anything regularly in that outlet and no abuse. One fact I omitted: Between Outlets #2 and #3 there's a chimney. It's been sealed off for decades and I regularly check the stack on the roof to make sure it's sealed and no water can get into it or that exterior wall. And I've never done any do-it-yourself work on any of the outlets on that circuit.

I will cut the power and inspect outlet #3 to make sure the wires haven't come loose.

[ZinscoMan]

Checked outlet #3. No loose connections. It is back wired instead of side wired but it's very tight and I didn't see any reason to change it. Everything looks brand new. No corrosion, no burn marks, no discoloration. Insulation on wiring not pinched or damaged. It hasn't made any buzzing in the last few days.

Buzzing was the symptom but symptoms can often point to more than just one potential problem. I've noticed in the past when standing outside near the transformer on my power pole that it can make a buzzing noise sometimes. Is it possible if the transformer were going bad it could send line noise through that circuit and be the cause of the buzzing?

[Stratmando]

Transformers will Hum, You don't have to do all this, but would either tighten on screws, or connect wires together and have a short pigtail to the receptacle. Backwiring is a Bad thing. Lazy.
You could turn off power to that circuit, remove wires from receptacle, cap ends off, turn power on and see if you lost power to other recepticles, the ones that now have no power go through that receptacle, to remove backwired receptacle, push something in slot next to insertion point, or rotate wire back and forth whil pulling on it. Then I would break open that recpticle and look at the discolored or burnt spot on it, as well as on the wire. Good connections make no noise.
You can wait until you hear it hum again, then turn off items downstream of #3, the humming should stop, confirming it WAS bad. You can't see the connection as it is in receptacle. Good Luck.
If you were to go through house and correct all the backwired devices, may consider changing receptacles to Decora Style? Good Luck