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Old 01-24-2017, 02:07 PM   #1
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Why did my transfer switch fail?

Recently, with my MH winterized in my rv garage and connected to 30 amps through a Surge Guard model 34850 and a 30 amp dog bone, my transfer switch failed and over a period of a couple of weeks, drained my 6 6v Interstate batteries to almost 0. I replaced the batteries and purchased a new transfer switch and had it installed. All is working fine now.

However, what would cause my original transfer switch to fail....and only the shore power relay as the generator relay was fine?

Any and all info would be greatly appreciated.

Ron, Sandie and Lilly
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Old 01-24-2017, 02:24 PM   #2
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2nd verse same as the first
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Old 01-24-2017, 02:24 PM   #3
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Did the power drop to low voltage for an extended time? That could do it.
Happy Glamping, Norman & Elna. 2008 Winnebago Adventurer 38J, W24, dozens of small thirsty ponies. Retired after 40 years wrenching on trucks! 2010 Ford Ranger toad with bicycles or KLR 650 in the back. Easy to spot an RVer, they always walk around with a screwdriver or wrench in one hand!
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Old 01-24-2017, 02:24 PM   #4
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Do you switch between shore / generator power with hi load appliances running?
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Old 01-24-2017, 03:04 PM   #5
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Originally Posted by 96 Wideglide View Post
Do you switch between shore / generator power with hi load appliances running?
I guess a better question be what your normal procedures were for hooking and unhooking from shore power. Also what your procedures are for starting your generator. You may have done nothing wrong and then again maybe you did something that helped with the early demise of your transfer switch. I know they just fail and certain brands and models are more prone to failure.
Your info could possibly save some of us from doing something similar that is harmful to our transfer switch. I personally never start the generator while the power cord is plugged into shore power. I also make sure all 120 volt loads are off before plugging in or unplugging or starting the generator. I also make sure the shore power breaker is off when plugging in.
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Old 01-24-2017, 03:09 PM   #6
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Originally Posted by 96 Wideglide View Post
Do you switch between shore / generator power with hi load appliances running?
That'll do it.
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Old 01-24-2017, 03:22 PM   #7
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What brand and model of transfer switch did you have? What did you replace it with?

Also, I assuming that once you lost shore power your Inverter must have kicked in and that's what drained your house batteries. You must have had some significant loads on the Inverter plus whatever 12 VDC you were consuming.

Not sure if you have an AGS or not but if you did then it would have saved your set of batteries by triggering the generator to keep the batteries from discharging too low.

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Old 01-24-2017, 04:22 PM   #8
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Inside the transfer switch, are a number of metal contact points, which switch back and forth and connect either the generator to your circuit breaker wiring/box....or the shorepower to the the circuit breaker box. There is set of contacts for leg 1, a set of contacts for leg 2, and a set of contacts for the neutral line.

Any time there is current going thru those contact points, and they open up because the switch 'switches' from one source to the other.....they will arc/spark (think arc welder). The more current, the larger the spark.

Those sparks over the months/years, eat into the metal of the contacts, causing them to have a higher resistance, until at some point they don't make a connection anymore. When that happens, the electricity doesn't pass thru the transfer switch, the charger doesn't get power, the batteries don't get charged, and will eventually go dead.

How to avoid? Turn off all coach current before allowing the switch to occur. Many people find that a pain, and therefore turn off at least the high current devices (Air conditioners, H2O heater, converter, Mwave, coffee pots, etc). When powering back up...wait for the transfer switch to switch/engage, then turn the devices back on.

The circuit board for the brains could also go bad, but the contact(s) problem listed above is typically what happens.
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Old 01-24-2017, 04:38 PM   #9
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There are a lot of reports on this and other forums of finding loose connections in transfer switches. It's a good idea to check connections yearly.
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Old 01-24-2017, 05:05 PM   #10
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I would go with the loose connections ruining transfer switchs. Seen many pictures of them, on this site, of melted wires.

As far as the points " welding ", how is it that my rooftop AC can switch the compressor on and off many times a day, with a tiny relay, and a large transfer switch, rated to switch its full load, allegedly can't do it occasionally.

The contactors in transfer switchs look just like motor starter contactors, used on air compressors and other high HP electric motors. They switch all the time.

It being an AUTOMATIC transfer switch, it should do it's job, without physically switching thing on or off.

I am testing that theory and have been for 2 1/2 years. I let the switch handle the load. I'll let you all know if anything burns out.
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Old 01-24-2017, 05:49 PM   #11
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I had a problem with our switch awhile ago. Coming from a car show we were going to stay at a wally world. Went to start gen and no power to coach. Open up the switch and used DW finger nail file on the contacts in the switch and everything fine. Has happened once since then. Just no need to replace switch, just clean.
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Old 01-24-2017, 06:14 PM   #12
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Originally Posted by twinboat View Post
I would go with the loose connections ruining transfer switches. Seen many pictures of them, on this site, of melted wires. ,,,
I agree. Moderate amp relays the size we have are used in lots of applications lasting years constantly switching under heavy loads. Worst case after thousands of state changes you might get a bit of pitting or some carbon that is easy to burnish off. Either way without more info we're all guessing. I would venture to say being man made doesn't help.
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switch, transfer switch

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