Transfer Switch not staying engaged

[Mike Shumack]

When I plug into Shore Power my Transfer Switch will normally make a "wump" noise as the contacts engage.

The other day when I plugged in, the Transfer Switch would not stay engaged, every couple of seconds it would "Wump", "Wump", "Wump"...
I unplugged the Shore Power cord and replugged, but no change. I thought the "dog bone" adapter might be the issue so I tried a different one. No change (I have the Shore Power plugged into a 50-to-30A adapter, and that plugged into a 30-to-20A adapter.

Then I checked the Inverter status and it was On (I usually leave Inverter Off). Would it matter if Inverter was on or off? I turned off Inverter and when I plugged the Shore Power cord back in it stayed engaged this time. Maybe just coincidence.

So I'm wondering if leaving the Inverter On could be causing the Transfer Switch to cycle - although there really aren't any loads On in the coach for the Inverter to power.

Last year I checked and torqued all the wires in the Transfer Switch (nothing was loose).

Is this a sign that something is beginning to fail. Has anyone had this issue?

[Mike Shumack]

After reviewing the wiring diagram - I don't see any relationship between the Transfer Switch and Inverter. Transfer Switch is only looking at Shore Power and the Generator as a power source.

I'll do some more testing but I think if there is a problem it must be in the Shore Power cable (or adapter plug) or power reel mechanism.

I did see a post somewhere about someone having a problem with the "rotating contacts" in their power reel going bad (corrosion/pitting) but it doesn't look the Cable Master reel uses a rotating/wiper style contacts (the cable appears to be one-piece from plug end to transfer switch connection).

[Fred Brooks]

   Mike,
  The Inverter/Charger has a pass thru relay when on shore power. When the inverter senses shore power, the inverter goes into "standby" and allows the shore power to pass thru it on the way to their respective loads. It also turns on the charger to go thru a charge cycle. I think the transfer relay may be on the way out or if it is the kind with the built in surge guard it may be sensing an issue with incoming shore power. Let us know what you figure out. Fred

[Mike Shumack]

Thanks Fred.
You may be right about the incoming power being the issue. My coach uses the "Surge Guard (model 40250)" transfer switch, which does monitor incoming power.
I'm running a heavy extension cable from my garage to where I park the coach - about 100 feet of extension cable. Maybe I have excessive voltage drop.

Any thoughts on how I can test the incoming power?

I'll start with a voltmeter in the receptacle where the extension cord is plugged in at the garage and compare that to the voltage at the other end of extension cord (checking voltage drop) - and/or check the voltage at an interior wall receptacle to see if any difference in voltage between garage receptacle and the coach receptacle.

I'll also review the Surge Guard owners manual and see what it is protecting against (low voltage protection limits, etc.)

[Lee Welbanks]

Mike, When we lived at the other house I had to use a 50' 50 amp four wire extension to reach the coach. It always worked fine until one time when we came back, plugged it in and the coach would not power up through the transfer switch. After much testing and such found that the neutral blade in the plug to the box on the house had basically overheated and coated itself no allowing the blade to make a good contact. I took the plug apart and the cheapo neutral lug was burnt up causing all the heat. Replace the plug end with a quality unit no problem since.
I believe the plug had gotten damaged while we were at a friends place plugged into their shop in the summer running all the A/C's and such.
The Camco 50amp plug ends are junk and really not rated to handle 100 amp power if you are using up both legs.

[Fred Brooks]

    Mike, I agree with checking line voltage at any duplex downstream of all the loads. As I recall, I think surge guard rejects voltage below 105 or somewhere around that threshold. Another consideration is to turn down the charger at the monitor panel to 5 amps seeing how it is just parked and stored at this time. Is the 100' extension cord a 10 gauge? Hope this helps, Fred

[Gerald Farris]

Mike,
The shore power reels that have an issue with contacts is the type that actually load the cord onto a reel https://www.rvupgradestore.com/Cablemaster-Motorized-50A-RV-Power-Cord-Reel-p/CRR50-12.htm?msclkid=889ee27daa7d1bc106a2bc0d748d29e1 not the type that you listed that use rollers to load the cord into a cord locker.

There is a very good chance that your transfer switch is disconnecting because of a voltage drop in the long extension cord that you are using when there is any load in the coach like the battery charger in the inverter or a refrigerator.

Gerald

[Mike Shumack]

Thanks for the suggestions.
I have not had this problem before (well, maybe once). I will lower the charging rate now.

The extension cord I use is a 10GA.
This one (from Amazon)

[Bill Lampkin]

Mike, Check the cord ends for excessive heat while in use. The RV style blade cord ends are notorious for high resistance (and high heat). The ones I've used over the years partially melted, so I changed all to 30a twistlock cord ends. Three prong, 30a, 250v. Not sure the NEMA designation, but the big box stores have them. Since swapping them out, no more high resistance cord connections. After seeing the heat and melting the blade type can cause, the blade type should be forever banned from the planet!

[Joel Ashley]

Gerald’s theory, about there being a load on the system when you’re plugging in, was exactly what crossed my mind when reading your original question right when you posted earlier this morning.  But not being as knowledgeable about transfer switches I opted out of responding then.  A small motor or other load somewhere cycling on and off might cause the symptom, but not if it was off when plugging in.  Thanks Gerald for bolstering my confidence a bit. 

I use a 12 gauge when an extension necessitates beyond my 50 amp built-in and 30 amp add-on cords, but length has a lot to do with voltage drop.   Even a 10 gauge if long enough could limit adequate voltage to certain loads.  And as Bill notes, a weak or aged adapter between cords can mess up complete power flow, converting too much to heat.  Been there, done that.

Joel

[Eric Maclean]

Mike
Remember even a bad connection or under sized wire can show good voltage with no load applied the volt drop is dependent on load.
It sounds like you have a load somewhere in the coach on startup creating an inrush of current which inturn creates the volt drop which triggers your surge protector to drop out (too much volt drop)
My first stop would be your inverter ( battery charger).
At any rate make sure you check volt drop at an outlet with a load applied somewhere in the coach I'd turn off the battery charger to set your base line and then turn it back on and monitor volt drop as I ramped up the charger output limit of course this assumes the batteries need a good absorption charge.
If the voltage drops below 105 volts the surge protect should drop out as designed unfortunately once the load is disconnected the voltage will jump back up and the tranfer switch will try to reconnect. This is the tump thump you hear.
Maybe it's time for that new 50amp park power post out there by your coach. Lol
Good luck
Eric