Genset when Plugged in to Shore Power?

[rpasetto]

Doing my Genset maintenance this AM and, as always, after filling up the oil I disconnect from shore power before starting up the genset to test it.

I recall being told that it's "perfectly OK" to stay plugged in to shore power as the transfer switch will switch over to the genset. Of course I realize that, in the (unlikely?) event that shore power and genset were to "connect", lots of stuff would get blown away.

Opinions? Anyone ever run into a problem leaving shore power plugged in while starting the genset?

[Our Time]

When I run the generator while connected to shore power, I open the breaker on the generator so it does not apply power to the coach.

[Bill Adams]

There is no need to connect, disconnect, power up, power down, switch breakers or anything else when you start up or power down your generator "assuming" that you have an automatic transfer switch. The transfer switch will choose the generator as the primary connection when it comes on and will default back to shore power when the generator is powered down. If neither is available the inverter will kick in.
When powering a generator on I generally do nothing as the transfer is instantaneous. However, in my coach but not all coaches, the transfer from generator to shore power does cause a momentary power interruption. Because of this I will power off the A/C units (that's all) before shutting down the genset and then power them back on once I have good shore power. Otherwise, there is nothing that needs to be done.

[rpasetto]

Yeah, but what if the Xfer switch fails and locks in the genset before disconnecting shore power? ... even if only for a few milliseconds? What can happen?

[Diplomat Don]

I did it once by accident when I was excercising the generator. It tripped a couple of citcuits. I decided it just wasn't worth taking a chance. I NEVER operate them together.

[fansill]

Ditto to Bill Adams answer... I attended a seminar this weekend at an FMCA Rally and one of the RV Techs said the exact same thing. He said that on newer coachs with the automatic transfer system, the Gennie will override any shore power. But I also, shut off anything that I feel will be affected by the momentary lapse of power as the two systems pass off on one another.

Just reporting what a supposed expert said....

Faith

[Mr_D]

Quote:

Originally Posted by Our Time When I run the generator while connected to shore power, I open the breaker on the generator so it does not apply power to the coach.

What does that accomplish? The gen set needs to have about ½ load applied while running to heat up the windings enough to burn off the moisture. If you're not doing that then no need to run the engine. You run the gen every month, the engine itself doesn't need it, the windings do.

[rpasetto]

Quote:

Originally Posted by Mr_D What does that accomplish? The gen set needs to have about ½ load applied while running to heat up the windings enough to burn off the moisture. If you're not doing that then no need to run the engine. You run the gen every month, the engine itself doesn't need it, the windings do.

Yes Mr. D, that's why genset manuf. states to run "under load". I was talking about running genset after oil change, just to check for leaks. I don't know if that was what Our time was talking about.

[LVJ58]

Hi Rick,

We also have an ATS on our coach and although it's designed to automatically switch to the priority power source input, there's always the potential for failure in any electromechanical device, therefore I always disconnect from shore power before firing up the generator when exercising it under load.

It requires very little effort on my part to disconnect the shore power plug and I feel more comfortable doing so.

[Bill Adams]

Some people like wearing a belt and suspenders. It's never necessary, but you can't argue with the folks that believe they need them!
If you live your life questioning what could happen "if", you would never leave your house! I did have a transfer switch fail a few years back. When it did, only the shore connection worked. If I powered up the genset (connected to shore power or not) nothing happened, it just didn't switch. No harm, no foul (and no power).

[BigSkyBob]

I'm with Mr. Adams. I have never disconnected shore power when exercising the generator. The transfer switch is not a fail safe device but a failure is very uncommon and will usally fail on one side in the open position. The only thing I do is disconnect ALL loads so there is no arc at the contacts when the switch is made, then apply a 50% load for an hour.

[jablair]

The ATS uses "break before make" contacts. Meaning it is highly unlikely, even with a mechanical failure, that the two input sources would both be connected. Suppose anything is possible, but highly unlikely. Like Bill Adams said, some people will still want or need to take the extra precaution. It is certainly not going to hurt anything even if unnecessary.

[Our Time]

When I run the generator for oil change, coolant change, etc while connected to shore power I open the breaker. I do load the generator up on a periodic basis, however I have popped the breakers for the energy management system when switching from shore to generator. Before I switch from one to the other, I turn off the generator or shore power. To me, it's not worth the chance of a major power flux.

[azstork]

I'm with Bill Adams on this one - I have taken apart the Transfer Switch on my HR and I think it would be impossible to have shore power and generator inputs connected together - The line to the coach is attached to the center contacts of a relay-energized switch - When the generator is "OFF" the contacts will by default go to the shore power input. If the generator is started, the transfer switch will sense the power in the generator input and after a time delay to allow the genset to get up to speed, it will energize the relay to pull the contacts to connect the coach line to the generator input - It will automatically and simultaneously disconnect the shore power input. If the transfer switch does not work correctly, the contacts will stay in the coach to shore power position, but will not and cannot connect both inputs together. Even if there is arcing that sticks (welds)the contacts in one position, it will still not connect the inputs together. Hope this makes sense.