What the Heck Is It? (and why is it buzzing)

[Beatbox]

Okay, so in my basement/workshop I noticed that every time my central AC kicks on there is a loud buzzing for about a half a second. It seems to have gotten louder/longer over the past few weeks.

I removed some ceiling insulation from where the sound was and found this. I have no idea what it is, but apparently related to the phone system. It has one line going out to my phone box (which i've disconnected), another line going to an old alarm system that is disconnected and un-powered, and a single wire that travels a few feet and is bolted to the outside of metal conduit. (ground?) I can't see any wires going to a powered source. So....

2) What is it?

3) Why does it buzz when the the AC turns on (20A, dedicated circuit)

4) Where could the power be coming from?

Any guesses are appreciated.

 

[rlitman]

Looks to me like some sort of lightning arrester on your phone line. No, it should not be buzzing.

My guess is that you have a ground fault in your AC somewhere. But that's just a guess.
Could be a failing start cap in your AC too. AC (this time as in alternating current) capacitors can emit some RFI as they're starting to fail (from internal arcing) that could be picked up by devices nearby.

 

[Milton Shaw]

My folks house had one of those lightning devices in their house. Dates from the 40's or so... It has a couple of carbon bricks in it that were what burned out. I don't know why it would be buzzing so do look at the A/C for wiring problems such as an open neutral or bad ground.

 

[Alchymist]

Old style phone lightning protection- should be no connection to AC anywhere.

 

[Lassen Forge]

My folks house had one of those lightning devices in their house. Dates from the 40's or so... It has a couple of carbon bricks in it that were what burned out. I don't know why it would be buzzing so do look at the A/C for wiring problems such as an open neutral or bad ground.

^^^ this.

Something is backfeeding AC into it, which isn't good. Check your wiring, and check the leads from the arrestor block for power when the AC kicks on. I bet something is energizing that thing, either a reversed neutral or a ground used as neutral.

 

[Fixin'Stuff]

Are you sure it's that thing that is making the noise? It looks like your breaker panel is just below it. The circuit breaker feeding the a/c compressor will buzz when the a/c first kicks in because of the huge inrush current as the compressor comes up to speed.

 

[BillK]

Is is "buzzing" or maybe just vibrating ? See if all of the screws holding it to the joist are tight and check all the connections too.

Like someone else said, are you absolutely sure that is what is making the noise ?

 

[Beatbox]

Thanks all so much for the input! I went back and checked. You were right, it is not coming from the, what I guess is a lightening arrest.

It appears to be coming from the conduit (here in no-Romex Chicago). Other places have suggested that it is just the wires rattling around caused by the brief hi-current draw from the compressor. I'll try to find someone local to look at it. It's just a nasty/grating sound.

(unfortunately, you can't upload vid/sound here)

 

[rlitman]

If the conduit is vibrating, I would suggest getting some conduit straps and just making sure it isn't able to move. That should settle the noise down.

 

[ABSTIFFGS]

We just moved into a new (to us) home. I have noticed my ac also makes a "buzz" sound for about a second when it kicks on. My thought is that it is the compressor starting. It goes away and system seems to work very well.

 

[snappytom]

Similar situation whenever our hot tub kicks on it's auto cycle. The 50A breaker makes a split-second buzz sound as the pumps fire up. Been doing it for years and never had a problem or overload.

 

[Tim C]

When the big compressor at my buddies shop kicks on you can hear a loud buzz and feel the conduit vibrate all the way between where the power goes out to the compressor out back and the breaker panel, probably 30-40 feet. It seems like the actual wires are vibrating inside the conduit. It stops after the comp comes up to full speed.

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