Unplug shoreline prior to starting generator?

[Gyrophoenix]

Is it better for the ATS (automatic transfer switch) to unplug the shoreline prior to starting the generator, or not?
Inquiring minds want to know....
Thanks.

 

[Tom]

Is it better for the ATS (automatic transfer switch) to unplug the shoreline prior to starting the generator, or not?
Inquiring minds want to know....
Thanks.

One purpose of the ATS is to eliminate the need for you to unplug from shore power.

 

[Laura & Charles]

I always kill any serious load (A/Cs, microwave, space heater, etc) before switching between any of the three 120 volt sources (shore, genny, inverter).

I’m curious why you want to start the genny if you have shore power? Is it just as you’re getting ready to leave? Exercising the genny?

 

[Gyrophoenix]

Exercising the genny. The consensus seems to be it can be left plugged in when the genny is started, without anything bad happening.

 

[Kirk]

The issue for your ATS is the amount of current that is being drawn at the time of transfer. As long as you do not have any large loads in operation when you start the generator, it shouldn't be a problem but if you have one or two air conditioners running, or the microwave, or even a lot of appliances it then will cause arcing of the ATS contacts. If the house batteries are being charged from a low voltage, that too can cause a large 120V load. How big the load is when you start the generator and how frequently you do so will determine the amount of damage that is done. By unplugging before you start the generator you avoid any arcing at all. As a general practice, I did not normally start the generator until the shore power was disconnected but on occasion I would leave it connect and just make sure no major loads were in use. If just exercising the generator, I usually opened the circuit breaker at the power pedestal before starting it. In 14 years of owning our last class A, I never experienced any ATS issues. It is impossible to say for sure that what I did prevented issues, but I believe it at least played a part.

 

[Gyrophoenix]

Excellent input. Thank you very much.

 

[Lou Schneider]

99% of the time there won't be any trouble but you risk sending a surge through anything powered up if you switch from one hot source to another. AC changes from +120 volts to -120 volts 60 times a second and since shore power and the generator are not synchronized with each other one source could be at +120 volts while the other is at -120 volts, creating a brief 240 volt surge when you switch from one to the other.

Commercial installations monitor the phase of both sources and only change from one to another when both of them are in phase with each other

 

[Kirk]

Another consideration is shore power and the generator are not synchronized with each other.

That is an excellent point and one that I should have mentioned. In my Navy days I was one of the operators who made such transfers, yet I overlooked that part. That too is a key reason for not changing with an air conditioner operating!

 

[OldWEB]

Is it better for the ATS (automatic transfer switch) to unplug the shoreline prior to starting the generator, or not?
Inquiring minds want to know....
Thanks.

Man some people like to go waaaaayyyy overboard. It is a momentary power outage, one that can happen anytime without any intervention from the operator.
Any "off"-"on" operation can be hard on electronics, just minimize your grief by shutting things down, if you want, disconnect shore power.
But I would turn off any air conditioners and residential fridges due to the compressors involved, any outage to them will cause them to try and restart while pressurized, and that ain't going to happen right aways, give them 10+minutes before turning them back on. DC powered compressors would be the exception.
Sheeeesch.....

 

[Kirk]

any outage to them will cause them to try and restart while pressurized,

Modern ones have had a delay built into them to prevent that from happening for a long time. The Dometic a/c units in our 1998 Cruise Master both had it. But the out of phase that Lou mentions is the reason for turning off anything with an alternating current motor.

 

[OldWEB]

out of phase refers ONLY to two items with voltage on them, don't try to sound smart, not working.

 

[xrated]

out of phase refers ONLY to two items with voltage on them, don't try to sound smart, not working.

Actually, if you have a 50A service coming into your RV, the two 120VAC power leads are 180° out of phase with each other while on shore power.....at least in the US it is. I have zero knowledge about electrical service in Canada.

 

[OldWEB]

Another smarty.... totally different scenario.
Ooops, but you are technically right, as I mentioned, there are TWO voltages involved in yer "example".

 

[Kirk]

I have zero knowledge about electrical service in Canada.

I'm pretty sure that all of their standards are the same as in the USA. And you are smart.

 

[OldWEB]

The OP just asked a simple question of transferring power from SP to jenny. It is built to do just that, hence the term Automatic Transfer. In a simple RV system, the compressors are all I would worry about, they do not like to re-start, no different in the S&B either. Just be kind and disconnect them first, also if the jenny does not perform properly, you do not want the possible low voltage trying to start them either, turn off TVs to be safe. Most systems in a RV are run off the DC so that will not be immediately affected from an outage. If you have one of those AutoStart features for the jenny, always good to exercise them how they are meant to run.
So no destroyer generator phasing scenarios, back-EMF horror stories, charged cables a half mile long feeding the underground pedestal.... just a simple autotransfer relay, no more.

 

[jymbee]

Man some people like to go waaaaayyyy overboard.
Sheeeesch.....

... don't try to sound smart, not working.

???

 

[John From Detroit]

Some things (Mostly air conditioners) can create havoc if you "Hot switch" to/from shore/generator power... Turn them off first or shut down power for at least 3 minutes is best advice.

 

[xrated]

I'm pretty sure that all of their standards are the same as in the USA. And you are smart.

They very well could be, but since I've never been to Canada, or had any desire to learn about their electrical grid, that is why I stated what I stated. I try to not post things that I don't know something about, and I'm at a zero when it comes to the Canadian electrical grid and how they do things

 

[jymbee]

I try to not post things that I don't know something about...

Whoa!

If everyone felt that way the Internet would be... well, actually a better place I suppose.

 

[xrated]

Whoa!

If everyone felt that way the Internet would be... well, actually a better place I suppose.

LOL....it probably would, but it wouldn't be half as entertaining as it is I suppose. I've been a Journeyman Electrician since 1980 and I know some stuff about that, but trust me, no one knows everything and I CERTAINLY include myself in that category of not knowing everything about electrical stuff. For example, I'm probably (just a guess here) in the minority of folks on here that know little to almost nothing about the solar end of the electrical stuff, if they have the background in electrical that I have. I really have no desire to learn it as it just doesn't interest me. My thoughts are.....I contribute when I can and if I have something worthwhile to offer. I also ask for help from others when I am trying to figure out something that I'm lacking knowledge about. It seems to work for me....help when I can, and ask for help when I can't.