Gen and shore power

[kuzined]

Never did it but was told that if the generator is started when you are plugged into shorepower, a lot of damage would happen. Just wondered if that is true.

[dougrainer]

Blaster Man wrote:

jplante4 wrote:
...Only if the transfer switch doesn't do what it's supposed to. This switch is supposed to cut out gen power when the shore power comes on.

...

My coach is the opposite, gen power take precedence over shore power.

ATS switches come from their maker with Genset as priority. But, there is a toggle switch inside the ATS that will make Shore Power priority. Some(very few) OEM's will flip that switch to make Shore Power priority. Doug

[Blaster_Man]

jplante4 wrote:
...Only if the transfer switch doesn't do what it's supposed to. This switch is supposed to cut out gen power when the shore power comes on.

...

My coach is the opposite, gen power take precedence over shore power.

[MrWizard]

The transfer switch on the RV is there ONLY so you don't have to do the manual plug switch
It is not there to switch power sources under load..aka A/C is running
This causes arcing and pitting on the relay contacts
It's only a matter of time before it malfunctions because of this

Yes they are make before break
But most do not have mechanical interlock , and many 50 amp switch have two relays in the box, with out mechanical interlock if one set sticks, both can be connected
Do this with two power sources and you are going to blow up a generator

It has happen..It has been posted
They were non believers before it happen to them

[dougrainer]

holstein13 wrote:

wolfe10 wrote:
If you have an ATS (Automatic Transfer Switch) and it is functioning properly, no, a "lot of damage" will not occur.

But, there are less stressful ways to do it. From an electrical standpoint, transferring under heavy load WILL cause an arc as one connection is broken and the other one made. That pits the points. Same reason you turn off the CG breaker before plugging in your shore power cord and before disconnecting-- so you won't arc the prongs.

Also, as with any engine, it is better to allow it to warm up a little before applying full load. The generator is no different. Can you start you car or coach and immediately go to wide open throttle-- sure, but not very good for them. Same for the generator.

Best practices: Turn off heavy loads before disconnecting from shore power. Disconnect. Start the generator. Let it run for 3-4 minutes, then add loads one at a time.

And, when turning off the generator, turn off the loads and let it cool down for a few minutes before shutting off the generator.

Great point. My coach does this automatically. If I turn on the generator while on shore power, the first thing it does is kill the A/Cs, then preheats the generator, then turns on the generator and after warming up, turns back on the A/C circuits.

Interesting, You have a Fleetwood still? I have NEVER seen a Genset start that when pushing the Genset start button would kill the roof AC units or ANY 120 system in the RV. Now, if you have an EMS system, it may kill the SHED side appliances, but ONLY when the Genset 12 volt run light signal is activated. Doug

[dougrainer]

Lets talk REAL world experience. I have been working on motorhomes as a professional for 35 years. In that time, I have seen Motorhomes before they had auto transfer switches that had manual breaker kill transfer and the old standard 30 AND 50 amp plug in receptacles in the power cord compartment that you plugged in the shore power cord to get Gen power to the RV. Then, they developed Auto transfer switches(30 and 50 amp models), I have started Gensets with Shore power connected. I have connected Shore Power when the Genset is running. I have done this at least thousands of times over the 30 years auto transfer boxes have been available. At no time did anything burn up or a catastrophic event happened. IS IT POSSIBLE? Yes, but extremely remote. As to what an Owners manual states. That it a CYA disclaimer. That just attempts to remove any possible responsibility and to deny a claim if something happens to the 120 side of the RV or appliances. There is NO way if something happens that they could pinpoint the problem to attempting to run the Genst while plugged into Shore Power or Vice/Versa. Doug

[holstein13]

wolfe10 wrote:
If you have an ATS (Automatic Transfer Switch) and it is functioning properly, no, a "lot of damage" will not occur.

But, there are less stressful ways to do it. From an electrical standpoint, transferring under heavy load WILL cause an arc as one connection is broken and the other one made. That pits the points. Same reason you turn off the CG breaker before plugging in your shore power cord and before disconnecting-- so you won't arc the prongs.

Also, as with any engine, it is better to allow it to warm up a little before applying full load. The generator is no different. Can you start you car or coach and immediately go to wide open throttle-- sure, but not very good for them. Same for the generator.

Best practices: Turn off heavy loads before disconnecting from shore power. Disconnect. Start the generator. Let it run for 3-4 minutes, then add loads one at a time.

And, when turning off the generator, turn off the loads and let it cool down for a few minutes before shutting off the generator.

Great point. My coach does this automatically. If I turn on the generator while on shore power, the first thing it does is kill the A/Cs, then preheats the generator, then turns on the generator and after warming up, turns back on the A/C circuits.

[wolfe10]

If you have an ATS (Automatic Transfer Switch) and it is functioning properly, no, a "lot of damage" will not occur.

But, there are less stressful ways to do it. From an electrical standpoint, transferring under heavy load WILL cause an arc as one connection is broken and the other one made. That pits the points. Same reason you turn off the CG breaker before plugging in your shore power cord and before disconnecting-- so you won't arc the prongs.

Also, as with any engine, it is better to allow it to warm up a little before applying full load. The generator is no different. Can you start you car or coach and immediately go to wide open throttle-- sure, but not very good for them. Same for the generator.

Best practices: Turn off heavy loads before disconnecting from shore power. Disconnect. Start the generator. Let it run for 3-4 minutes, then add loads one at a time.

And, when turning off the generator, turn off the loads and let it cool down for a few minutes before shutting off the generator.

[mowermech]

kuzined wrote:
Never did it but was told that if the generator is started when you are plugged into shorepower, a lot of damage would happen. Just wondered if that is true.

No, it is not true.

[holstein13]

I've done it a few times in my coach. I've started the generator while on shore power and I've plugged in while on generator. Of course the first time I tried it was at the dealer's lot with their guidance while taking possession of the coach. I figured if I fried it, at least the dealer would fix it.

Now that I know nothing bad happens, I wouldn't hesitate to start the generator or plug in at any time in any combination.

[dahkota]

we have an auto transfer switch. We are parked with 15A power right now. When I want to use something that will push us over 15A, I turn on the generator. I first turn off all significant loads then turn them back on when the generator takes over. Same thing just before we shut it down. We have been doing this about once per day for the last month and have had absolutely no problems.

[doxiemom11]

Our coach also has an automatic transfer switch. We also have an inside switch to start the generator. If it was required to outside and unplug first, there wouldn't be a start switch inside the coach.

[down_home]

Ours ,is like most or all I have seen. We have the gen running, with the ac running and plug in. Soon as juice from campground hits the generator cuts out.
When we leave we cut the gen on and unplug.
I wouldn't think, of running the gen, for a period, of time plugged in. No reason to. At most, it might run two or three minutes.
If you can't trust your transfer switch not much purpose in having it. imo

[DrewE]

I don't see how anything could be damaged by starting the generator while on shore power. If you have any significant loads active, you will be stressing the transfer switch and the generator, and so that would not be recommended, but it shouldn't in itself cause damage to anything. (For that matter, starting the generator or connecting to the line under load is not recommended regardless of the circumstances.)

The transfer switch is designed to be a break before make switch—that is, the shore power is disconnected before the generator is connected, and vice-versa. Directly connecting them together is impossible by the switches mechanical design. If the generator were directly tied to shore power, that would be very bad and would probably destroy the generator (and maybe other systems in the area). Bear in mind that the generator head is basically a large electric motor of five or more horsepower. Connecting it to the line voltage if it's not well synchronized first will cause a very sudden and very strong torque, and stuff will break. (What stuff? My guess would be the crankshaft or connecting rod of the generator engine, rather quickly followed by the generator electronics, but it's not something I care to experiment with to find out for sure.)

If starting the generator while on shore power were truly a big problem, surely the manufacturer would install an interlock in the starter circuit (which would be quite straightforward to do) rather than merely putting a line in the owner's manual that frankly many people won't bother to read.

[ksg5000]

All depends on how much trust you put in your transfer switch. I personally avoid trying to "test" the transfer switch --- not much upside and it not hard to disconnect shore power.