Tuesday, February 21, 2017

Replacing The Automatic Transfer Switch

Does your rig have a hardwired surge protector?  If so, you could have power at the source plug but nothing in the rig, it sounds like a bad ATS is a likely culprit.  While they usually fail in either Generator mode or Shore mode, I did have one that failed both ways.  If you can get the generator going and have power, but none with the shore power, it is almost certain to be the ATS.

Are your electrical skills up to working on the electronics?  If so, here are step-by-step instructions to check and to replace the ATS.  IF YOU ARE UNCERTAIN OF YOUR ABILITIES IN THIS AREA, DO NOT TRY THIS!

1) Cut the power. Check with a meter to be certain there is no 120v power in the system.

2) Remove the brown power panel cover using a Torx head driver.

3) There are 4 hex head screws going into the wood in the top left and right, and the middle left and right of the power panel frame. Remove them.

4) Slide the power panel toward you until it clears the frame and you can tilt it forward to see the ATS mounted on the back.

5) Open the top of the ATS.  This is usually done by loosening or removing 1 to 3 screws on the ATS cover.

6) Looking down into the ATS, you will see 3 bare grounds connected to lugs on the side, and you will see three white and three black wires connected to six lugs.  I will call them 1 through 6, left to right.  One, two and three are black and four, five and six are white. THIS IS POTENTIALLY DANGEROUS!  Turn the power on and use your meter to check voltage on the wires.  Check between #1 and #6, between #2 and #5, and between #3 and #4.  On my rig 1 and 6 are the power from the ATS to the power panel, 2 and 5 are the generator and 3 and 4 are for the shore connection. If yours is wired differently, make a note of how your wires connect, so you get it right at re-assembly.  With your rig connected to shore power, you should find 120v on the Shore connection pair, 3 and 4.  Once you find power there, check 1 and 6.  If there is no power there, the ATS is bad.  If you have power at 1 and 6, the ATS is working, and your problem is probably inside the power panel.  You need a pro. If you have no power coming in from the Shore Connection, your problems lie elsewhere, probably in your shore connection cable or its plug, its socket, or the plug on the wall of the RV.

7) Turn the power off. MAKE SURE IT IS OFF!

I have worked on 4 ATS's, and all 4 attached differently to the power panel. In one case I had to remove the breakers, drill out rivets, and drill new holes for the self-tapping screws mounting the new ATS.  I found a Parallax link at http://d163axztg8am2h.cloudfront.net/static/doc/f6/f3/baa96cf1c020f6f561dfa1303f92.pdf that may be helpful.

The basics are, loosen the 3 white, 3 black and 3 ground wire lugs.  Loosen the strain reliefs.  Remove wires, then remove the old ATS from the power panel.  Attach the new ATS to the Power Panel.  Re-mount the wiring, doing the grounds first, then 1 and 6 for the power panel, 2 and 5 for the generator, and 3 and 4 for the shore supply. Follow the torque settings for the lugs.  That is important. [See diagram below]

Gee - I sure made that sound simple.  When I did it, it has NEVER been simple. If it sounds confusing, challenging or intimidating, do not even try.  Get a pro to do it for you. If you screw it up, you can fry your panel, fry your shore cable, burn up your rig, or fry yourself. I say again, if this is outside your skill set, get a pro to do it.

OK, put the cover on the ATS, slide the panel back into position, put in the 4 screws and re-mount the brown cover.  You're done.

Ken F in NM

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