I have a fairly new house (built Sep. 02) with a 200 amp service
coming in. It is kind of long, so there is a subpanel about halfway
across the basement. I was moving junk around downstairs - we call it
organizing :-) - when the A/C came on. I have two AC systems (1st
flr., 2nd flr.). Whichever kicked on, the second before, there would
be a buzz from the subpanel the units are out of. Is this something
to worry about? I went over to the main panel and heard nothing. I
assume it has done this since the beginning of time, but since we
ussually only "organize" in the winter I have not heard it before.
Thanks for your help.
On 4 Sep, 10:24, firstname.lastname@example.org wrote:
Just a guess, since I can't see (or hear) your subpanel from here...
You could have a loose coonection and thus you might be getting some
arcing with the initial current draw.
I don't know how comfortable you are with pulling the cover, checking
connections, etc. This first thing I would do is pull the cover, turn
off the lights and have someone fire up the A/C. You might see the
arcing if it's a loose wire or breaker. If it's internal to a breaker,
then you might not see anything. The contacts and/or the thermal
magnetic components may be weakened.
You also might want to inspect the busbar that the breaker plugs onto
to be sure there is no discoloration or melting of the metal due to a
Slightly OT - When I was in the service I worked on transmitters that
had vacuum tubes with 15,000 volt plate voltages. It had big oil
filled capacitors that could handle up to 30KV. Sometimes the
transmitters would arc under normal power, but with the sheet metal
panels on you couldn't see the arcs. We'd wait until after dark,
remove the panels and run the power supply up to 20 - 25K trying to
cause an arc. Since there wasn't a lot of room surrounding the
transmitters, we were always within 8 feet or so. It's was pretty
impressive (and d*mn scary) when the arc occured. The things we did
for our country!
- What equipment have you worked on? I did same thing way back in the
- snip -
I worked on Loran-C transmitters in Germany and Alaska during the late
70's while I was in the Coast Guard.
- Sounds like the breaker is on the edge of tripping during the
- of the A/C compressor motor. Mine does that, too...
If the breaker is that close to tripping on startup, something is
wrong. The tolerance between amperage of a breaker and the normal
operating conditions of a circuit should not be that tight.
Note: By "normal operating conditions" I don't mean "steady state".
Normal operation includes start-up conditions as well as steady state.
I agree. Circuit breakers can hum. The current produces a magnetic field
which can cause parts to vibrate. When the compressor starts it draws
about 6x the running current. Higher current produces more vibration.
(A sizzling sound indicates a loose connection/arc.)
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