Transfer Switches - They're Nothing But Trouble Waiting to Happen

[Tom]

FWIW we have two transfer switches on our boat:

• The transfer switch/relay in the inverter that automatically switches to inverter power when external (shore or generator) power is lost, and vice versa when external power is restored. Can also be activated manually.
• An interlocked pair of ganged double pole switches (4 total) used to manually switch between shore and generator power. The interlock physically prevents either pair of switches from being turned on while the other pair is on.

Our coach has an automatic transfer switch to switch between shore power and generator. I sometimes wish we had that on the boat, along with the EMS. But both systems work just fine.

Like Mark, I always turn off loads (and/or their respective breakers) before manually plugging in/connecting or removing shore, generator, or inverter power. I spent too many years replacing relays, switches and contactors (used for very large loads) due to arcing-induced damage. However, the transfer switch in the inverter is supposedly designed for hot switching, but I'm still gun shy and turn stuff off.

If you want to see arcing on switches due to opening under load, check out the ACBs (air circuit beakers) used for switching high voltage power lines and stepped-down voltage to substations. I've only seen them in use switching 132KV, and it's been many years since I worked around them, but they use a blast of compressed air to "blow away" the arc during switching.

edit: fixed typos.

 

[rsalhus]

I figure it's bound to last longer if I'm kind to it.

Gary, that's kind of my philosophy too.  Easy does it, don't push it if you don't have to, I like to carry that kind of attitude to our MH.

Mark mentioned above how I started this thread with emphasis on how lazy we are for using the ATS instead of manually switching power sources.  From the replies above, it seems that most RV owners trust their transfer switches much more than I thought.  Maybe I too might be inclined to at least test our transfer switch more if our coach were still under warranty, but I don't have that luxury. 

And the fact that we haven't heard from many RV owners who've had problems with their transfer switches should probably make me believe that maybe they are quite reliable.  But I still don't understand Lou's statement that electrical power problems in RVs are easier to diagnose if the system includes a transfer switch.  That doesn't make a lot of sense to me. 

 

[Gary RV_Wizard]

The transfer switch is always a suspect when somebody complains they lost all 120vac power, but it is not often actually found to be the culprit. We did have one here this past week, however, so it can and does happen.

Most people don't know how they work, where they are, or even why they have one. In fact, some do not even know they have one, so it's not surprising they don't think much about them.  Those of us who have been discussing it here are techies to one degree or another. For everybody else, it's just some piece of magic in the background, visible only if it fails to perform its trick.

 

[Jim Godward]

I'll admit I haven't been following this thread but have popped in from time to time to see what is being discussed.  The comment about no one who has had failures commenting meant that I have to do so.  I have had both the main transfer switch fail and the one in the Heart/Xantrex inverter fail.  The main inverter failed one year in a park in Salome AZ, Desert Gold.  That failure meant we could not get the shore power into the RV, it failed set to generator.  The only way we could charge the batteries to survive was to run the generator whch the park allowd in the daytime as an exeption because of our problem.  It took a couple of days to get the part from Newmar, under warrantee as I did not want to pay for it but did pay $10 for overnighting the new one.  That suppler went out of business about a year before my transfer switch failed so got a better one. 

The failure in the inverter was due to an under rated part that was used.  It was rated for 30 amps IF properly heat sinked.  It is not and Xantrex would not sell just the part but required a circuit board be replaced by an AUTHORIZED dealer.  After we got it back, I found a direct replacement relay rated at 40 amps and repaired the "bad" board and then installed one in the new board too.

The first failure was after spending about a week out at the RV Forum rally and we needed the time to get ready for another rally, you know laundry, empty tanks etc. so that was a mnor inconvenience.  The second was in So. CA  and would have meant no lights, TV, etc. so I jumpered around the inverter till it was repaired.  It took about a week to get the inverter repaired.

 

[catblaster]

Jim, my freedom 20 failed from a power surge, repair facility wanted $500 to fix. (sound familiar) fixed it for $14 with a new transformer on the ac power board. easy fix...a caveman could do it. well..... a caveman with a soldering iron

 

[rsalhus]

I have had both the main transfer switch fail and the one in the Heart/Xantrex inverter fail.

Hi Jim, I was hoping we'd hear from someone about a transfer switch that failed.  And you've had more than one. 

You stated that the main inverter failed one year in a park in Salome, AZ.  Did you mean to say that the main transfer switch failed there?  If so, I have some more questions below.  I'm trying to learn something about failures in the main transfer switch primarily.

What were the circumstances leading up to the failure of your main transfer switch, if you recall?  Did you have a load on when your transfer switch switched power or not?  Were you switching from generator to shore power when it happened?  Sorry for all the questions.  :-[

 

[Jim Godward]

Jim, my freedom 20 failed from a power surge, repair facility wanted $500 to fix. (sound familiar) fixed it for $14 with a new transformer on the ac power board. easy fix...a caveman could do it. well..... a caveman with a soldering iron 

Yup, same board, same price!!  Mine wa covered by my service contract so I just paid the deductible.  That switching relay can be overloaded quite easily and usually the relay is OK, the solder bows out of one or more of the circuit board holes.  Usually you can fix that by just resoldering the board. 

 

[Jim Godward]

You stated that the main inverter failed one year in a park in Salome, AZ.  Did you mean to say that the main transfer switch failed there?  If so, I have some more questions below.  I'm trying to learn something about failures in the main transfer switch primarily

What were the circumstances leading up to the failure of your main transfer switch, if you recall?  Did you have a load on when your transfer switch switched power or not?  Were you switching from generator to shore power when it happened?  Sorry for all the questions.  :-[ 

Yes the main switch failed.  We were hooked up and all was well.  We left the park to do some shopping and when we came back, the power in the MH was off.  There had been a power failure while we were gone and when power was restored the transfer switch was damaged and failed to switch back to shore power.  The actual contacts were fine, the coil, electromagnet, that does the actual switch activation was bad.  Later when I examined it, the windings were not done properly and the increased voltage from one turn to the next eventually caused the failure.

The batteries were charging, probably the bulk charge current had been reduced by the time of the failure so only a few things were on, furnace and some other 12 volt stuff as well as the phantom AC loads.  In other words, not much AC draw, probably less than 10 amps or so.

If you need more information on this we can take it off to private eMail or stay here, your call.

 

[rsalhus]

Jim, thanks for sharing that.  I think this is good information for us to know, but I am a little confused about something.  Before the power went off at the campground where your transfer switch got damaged, you were connected to shore power.  Do you think the transfer switch was damaged by a power spike when the campground lost power or what?  Does the transfer switch get activated whenever power is restored after being down or only when switching power sources? 

 

[Gary RV_Wizard]

If I was stuck for a couple days waiting for a main transfer switch repair, I'd re-wire to either bypass the switch or use the other set of relays if only one side was out. Not that big a deal for anybody who can do a bit of electric work.

The ones in automatic inverter/chargers, though, are  tougher. Need that soldering iron, maybe a heat sink, the replacement part and a modicum of skill.

 

[Jim Godward]

Jim, thanks for sharing that.  I think this is good information for us to know, but I am a little confused about something.  Before the power went off at the campground where your transfer switch got damaged, you were connected to shore power.  Do you think the transfer switch was damaged by a power spike when the campground lost power or what?  Does the transfer switch get activated whenever power is restored after being down or only when switching power sources?

 

[Jim Godward]

If I was stuck for a couple days waiting for a main transfer switch repair, I'd re-wire to either bypass the switch or use the other set of relays if only one side was out. Not that big a deal for anybody who can do a bit of electric work.

The ones in automatic inverter/chargers, though, are  tougher. Need that soldering iron, maybe a heat sink, the replacement part and a modicum of skill.

Gary,

There was no real pressure to do that as I could recharge the batteries with the generator.  Working in the compartment is bad enough, I wasn't going to do it 2X!   

 

[Alfa38User]

......  But I still don't understand Lou's statement that electrical power problems in RVs are easier to diagnose if the system includes a transfer switch.  That doesn't make a lot of sense to me. 

I think Lou 's statement simply means that, with an easily accessible switch, it provides a perfect point to test the three 120V sources.  You can use a voltmeter on the 120V from the pedestal, for the 120V from the Generator and the 120V towards the distribution panel all from one spot. You can also easily bypass the switch at that point if it proves necessary. Otherwise, Checking the 120V within the coach is more of a PITA.

As a fifth wheel owner I don't have any of this, but, as a career techie (not on RV's though), this kind of arrangement is excellent for troubleshooting.

 

[Just Lou]

[quote author=Alfa38User]
I think Lou 's statement simply means that, with an easily accessible switch, it provides a perfect point to test the three 120V sources.  You can use a voltmeter on the 120V from the pedestal, for the 120V from the Generator and the 120V towards the distribution panel all from one spot. You can also easily bypass the switch at that point if it proves necessary.
[/quote]

Thanks Stu, you summed it up very well.  Additionally, while still in the initial analysis phase, one can make some intelligent assessments, based on the location of the switches within the circuit layout, of just where an electrical problem may exist.

Example:
If I have power (at the dist. ctr) from shore, but not from generator, then I can assume the problem is at/from the gen to the tx switch.  If I have power from Gen, but not shore cord, then I can assume the problem is at/from the pedestal to the tx switch.  If I have power from neither source it's a very simple matter (via quick disconnects) to eliminate or invoke the transfer switch in the inverter to further diagnose problem location.  I fully understand that the tx switch may be the actual offender in any of the scenarios stated, but determining that quickly is also a benefit.

Rolf, as Gary stated, not every RV'r is intimately familiar with their electrical systems and may not find anything that I've cited to be intuitive.

Whether the existence of a transfer switch adds or detracts from your diagnostic ability is as much personal opinion as is your position on the cost v/s convenience/reliability of the switch itself.

 

[carson]

I luv this thread. How does one fix or troubleshoot an AC electrical problem? I wish I had a XF switch so I could speak with authority. But I don't have one so I'll stay quiet.

  When shore power does not work, I simply check the breaker on the pedestal and go from there.

When the generator doesn't deliver power, it means I forgot to plug the cord into the receptacle in the power bay.

If I can't find the problem I'll go to the nearest pub and get a Sarsaparillo.    ;D

  Just trying to cheer everyone up.

Carson FL  Cold here 85.6?.

 

[rsalhus]

Whether the existence of a transfer switch adds or detracts from your diagnostic ability is as much personal opinion as is your position on the cost v/s convenience/reliability of the switch itself.

Lou, all I know is that when someone here has a power problem they are usually advised to first check the transfer switch.  So if there wasn't a transfer switch, it would seem that the diagnosis would be simpler.  My own diagnostic ability isn't all that great, that's why I like to keep it simple.  :-* 

I think I understand Stu's point too, but don't know about the accessibility factor in my case.  Ours is in the same basement compartment as the power cord and looks to have 5 metal screws holding the cover on, the same as zukIzzy's.  I could probably get the cover off without too much additional help, but oh, I see it's made by MagneTek.  Maybe I should just throw in the towel and put in a manual switching system or get a reliable coach like Carson's. 

 

[Just Lou]

Lou, all I know is that when someone here has a power problem they are usually advised to first check the transfer switch.  So if there wasn't a transfer switch, it would seem that the diagnosis would be simpler.

'taint necessarily so...  folks suggest checking the switch partly because you can learn so much by observing it's operation from various power sources.  Not simply because they always suspect it to be the source of the problem. 

Analogy:  When the light on your dash says "check engine", it implies more than raising the hood to see if the engine is still there.

Actually it's more like the observation of the switch can tell you whether the "prize" is behind door #1, #2 or #3, but can't always tell you exactly what or where it is beyond that.

My personal opinion is that if someone consistently suggests checking the tx switch for all power problem symptoms, just because they believe it to be the weakest link, should not even be posting on the subject.

If an operator of a coach, with NO transfer switch, reported no power from shore or generator, what would you suggest? ...I'll tell YOU...  You would have him check the breakers at the pedestal, at the generator and check the condition of the power cord plug.  Right?

You just had him check his transfer switch... 8)

However the problem may still be behind door #2 or #3.

IMHO, I can get to doors #2 and 3 faster by knowing what did and did not pass through the transfer switch.

Rolf, my mind is made up, please don't confuse me with facts.  I may seldom be right, but I'm never in doubt. ;D ;D ;D

 

[Alfa38User]

....  So if there wasn't a transfer switch, it would seem that the diagnosis would be simpler.  My own diagnostic ability isn't all that great, that's why I like to keep it simple.  :-* 

It might be, but not for me.... access to the various places necessary  to check this with a Voltmeter and with the switch is a LOT harder.  And unless you are physically unable to fit in the opening necessary to get to a switch and remove the cover, you would be right again.

That said, when yours goes, simply dump it.... and you will have your wish.  KISS lives on!!!!

 

[rsalhus]

Ok, so what have we learned here about transfer switches? 

• The first thing we've learned is that main transfer switches almost never fail
• The second thing that we've learned is that when main transfer switches do fail, stuck relays can leave you without the use of a power source, but transfer switches are cheap and last a long time and it's nothing to replace them or to reroute the wiring inside of one to get you back up and running
• And the last thing that we've learned here is that when you have an electrical problem and someone advises you to check your transfer switch, they don't necessarily want you to check for a transfer switch failure, they just want you to get the cover off and to check for a 'prize' in there behind one of three doors

Is that about it in a nutshell, Lou? 

 

[Just Lou]

Rolf, I must commend you on being such a quick study.   I couldn't have said it better myself.   In fact, I expect you to share your vast new knowledge and appreciation of ATXs with future forum members who might otherwise be left "powerless". 8)