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Old 01-11-2016, 10:31 AM   #1
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Hum from automatic transfer switch

Our automatic transfer switch is in a basement just below where DW sleeps. She hears a low hum or buzz from it, maybe all the time, maybe only some campgrounds, not sure. It bothers her. First, is this sound normal? Even if normal, any ideas for quieting it/muffling it?

Shell Bleiweiss
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Old 01-11-2016, 11:05 AM   #2
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If it's mounted directly to some hard surface in the basement, try mounting it so that there is rubber between the switch and whatever it's mounted to. Perhaps some rubber grommets that you can put the mounting screws/bolts through.
Or to test that theory, next time you're stopped remove it from its mount and just place it on something soft inside the basement. If DW can't hear it after that then you know changing the mount type (or location) will get you where you need to be.
My guess is that sound is traveling through the coach itself into you DW's pillow.

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Old 01-11-2016, 11:23 AM   #3
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If the humming has developed recently it could be a sign of dirt, moisture, or pitting of the contacts. After turning off all the power, including any inverter, you can remove the cover and clean the contacts with some electronic cleaner followed by compressed air. Take this opportunity to ensure that all wire connections are tight. If it continues you can try to isolate it from any hard surface as mentioned but it may need replacing if it bothers you to much. If you replace it as I had to do, make sure you get one with DC relays, much quieter than AC ones.
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Old 01-11-2016, 12:57 PM   #4
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Mine hums, I believe that is rather normal also.
2011 Monaco Knight 40PBQ towing a Jeep JK Rubicon Wrangler
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Old 01-11-2016, 01:06 PM   #5
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Some ATS's use 120 VAC coils to switch the contacts which will hum. Others use 12 VDC coils to switch the contacts and those do not hum.

A couple of examples are two of the ESCO transfer switches.

The ESCO model ES50M-65N uses the 120 VAC coils whereas the ESCO model LPT50BRD uses 12 VDC coils.

If this is a new condition that just recently started then do as a previous poster suggested and clean up the ATS.

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Old 01-11-2016, 01:17 PM   #6
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Originally Posted by sbleiweiss View Post
Our automatic transfer switch is in a basement just below where DW sleeps. She hears a low hum or buzz from it, maybe all the time, maybe only some campgrounds, not sure. It bothers her. First, is this sound normal? Even if normal, any ideas for quieting it/muffling it?
Are you sure it is the transfer switch?

My inverter/charger, (which is next to my transfer switch in a basement compartment under the bedroom), always 'hums" when my coach is connected to shore power and/or when the generator is running.... and when it's producing 120VAC...but my transfer switch never has.
'96 Safari
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Old 01-11-2016, 01:29 PM   #7
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All good inputs here--AC driven contactors in x-fer switches tend to hum more as they get older, so go with DC next time. New hum/louder hum could be a sign that x-fer will fail sooner rather than later. The charge function on most inverters will cause a hum--not much you can do about that......

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