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Old 11-09-2012, 09:10 PM   #1
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Noisy Power System Transfer Box

I have an electrical hum coming from my 50 amp Power System Transfer Box while Iím connected to shore power. Does anyone have any idea of what causes this, and how do I silence it?

2005 Dolphin
2012 Equinox
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Old 11-09-2012, 09:18 PM   #2
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Living with the same issue, I'm tagging along to see what answers you get .
Hopefully not $$$$$$

99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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Old 11-10-2012, 04:27 AM   #3
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I had the same hum in my old coach. Never got rid of it until I traded in the motor home and got a different one. Not sure if it was the kind of transfer switch but the new coach is silent, both in switching from house to shore power and while connected. Sorry, don't know the answer to your question either, I actually got to trust the hum to know it was connected. Since I store it in my back yard, a couple of times I realized there was a shore power issue by walking by the coach and not hearing the hum had blown the GFI's and shut down shore power.
Dan and Kathryn DeBruin plus dogs
2005 Newmar Dutchstar 4009
Victor NY
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Old 11-10-2012, 07:40 AM   #4
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We had the same Humm coming from the electric box area in the bedroom while plugged into shore line. Took the motorhome in and had to have the transfer switch replaced. The part had to be ordered so we had to leave the coach a few days. The part was about $700 but we had a warranty to cover it so only cost us $100 deductible. It fixed it because now there is no noise when we plug in. We never heard the noise when running off the generator so we figured it was something to do with the transfer to electricity.
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Old 11-10-2012, 07:52 AM   #5
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I have the exact same issue with my Fleetwood Bounder. I am taking it in to the dealer on Monday for them to finish the PDI corrections, I just added the transfer switch to my list.
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Old 11-10-2012, 08:16 AM   #6
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Generally speaking 50 amp transfer switches contain 2 heavy duty relays and a control board. The hum can be a common normal result of the relays coils being AC activated vs DC activated. Sometimes the relay contacts can get pitted/dirty by having to switch under hi loads. Recommendations are to minimize loads prior to "switching" to help the longevity of the contacts. Mounting isolation of the switch box can help or replacing with a DC coiled relay system can help as well.
1999 Newmar Mountain Aire MADP 4080, Cummins ISC 8.3L, Allison, Spartan MM IFS, Howard Power Center, Chev Trailblazer LTZ Towed w/ BlueOx rigging, Segway X2.
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Old 11-10-2012, 10:04 AM   #7
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Not sure if it's the same problem, but my MAGNETEK convertor always hums during use. It's just a fancy battery charger wit a big transformer to reduce the power down to the 12 volt level. The transformer is big and it hums. The newer convertors are solid-state and don't have the big transformer; they're lighter and quieter.

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Old 11-10-2012, 01:43 PM   #8
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The hum noise from the transfer switch is the result of either dust or rust between the two mechanical poles when the coil pulls in the contacts, the dust/rust prevents a clean mating of the two poles and the result is humming.
This can be eliminated by either purchasing new unit or taking apart the old and cleaning the pole shoes, Not the contacts, just the moveable poles.
BTDT for 40 yrs
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Old 11-10-2012, 07:37 PM   #9
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You do know that there is a recall on the IOTA ITS-50R 50AMP transfer switch. That could be your problem.
Dan and Micki (Dogs/Kids) Reece and Zoey
2008 Monaco Knight
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Old 11-11-2012, 08:13 AM   #10
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I just looked at my unit, I have a ES50M-65N unit so I don't have the one that's on recall. Most likely I'll take the unit apart and clean the moving parts as suggested, when I get a chance.
Thanks for all the comments and suggestions, this is what makes this site great.
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2012 Equinox
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Old 11-11-2012, 11:38 AM   #11
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I have a Surge Guard 41260 and it hums once in a while and I can only hear it when everything if quiet.

2012 Monaco Knight 36 PFT
2014 Jeep Grand Cherokee Overland
2005 Jeep Rubicon Unlimited on 2007 16' Car Hauler trailer
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