Generator question

[The_Logans]

Well, the power was out, so we (DW and 5 dogs) moved out to the 2015 Jayco Redhawk, and I cranked up the generator. It was all good, and the AC was humming along.

Then I began to worry... the MH was connected to the 30 amp house power, and the generator was running. What would happen when the power came back on? Would the shore power back-feed into the 4KW Onan and blow the diodes, or is there some sort of protection against that?

Any advice would be greatly appreciated!

[Toot_Mc]

we lived in our motorhome for a couple of week when we had hurricane a few years back. I did not hook up to house in any manner. i ran two extension cords to my ref g's but i unplugged them from the wall and plugged into the extension cord from motor home. saved our food and perishables. also saved all my neighbors frozen food also. had a 8KW diesel generator at the time had my ref g's and three neighbors all hooked up by extension cord only.

[Dusty_R]

http://www.interlockkit.com/ You can get one of these from here or the last couple years you can get them from most big box stores for much less. And they are approved by NEC. I've installed a couple.

Dusty

[maillemaker]

My new understanding is that in a modern Motor Home, unless there is a catastrophic failure of the ATS, no generator power can feed back through the 30a cable from the coach to the house. Likewise, when the power comes back on to the house, the current feeding into the RV's power center will be isolated there until the genset is shut down.

I guess that it's all pretty "idiot proof" these days.

This is precisely as I would expect. I would of course read my owner's manual to confirm all this if I had such a new-fangled thing, but this is precisely how I would imagine such a device would have to be engineered for liability reasons if no other.

Steve

[The_Logans]

Thanks to all...

My new understanding is that in a modern Motor Home, unless there is a catastrophic failure of the ATS, no generator power can feed back through the 30a cable from the coach to the house. Likewise, when the power comes back on to the house, the current feeding into the RV's power center will be isolated there until the genset is shut down.

I guess that it's all pretty "idiot proof" these days.

Thanks goodness for that! 🙂

[Capt_Storm]

They have it covered.

[maillemaker]

My old RV does not have an automatic transfer - I have to plug my shore cable manually into my generator socket to have gen power and clearly then it can't also be plugged into shore power, and vice versa.

But with a new-fangled ATS system, surely these people who have designed these things have isolated the systems so that if you're plugged into shore power AND your generator is also turned on that the ATS system can handle this situation safely and appropriately?!?!?

This would seem to be a fundamental part of any such design. You wouldn't want to try to apply double voltage to the RV and you wouldn't want your genset trying to back-feed the shore.

Steve

[Pauljdav]

One sure fire way to know if your gen is back feeding power into the house is if any lights are working in the house when the gen is on. If yes you are back feeding, if no you are not.

[Capt_Storm]

naturist wrote:

Capt.Storm wrote:
Good thought but yep,you're fine doing that.

NO! Wrong answer!!

YOU MUST UNPLUG THE CAMPER FROM THE HOUSE WIRING WHEN THE GENERATOR IS RUNNING. It is required by law, as well as common sense safety considerations. Somebody could get killed!

REALLY.

Here's the thing, power goes out at your house. Maybe it is because a tree fell on the lines. So what happens when the lineman goes to repair that line, grabs the end that goes to your house (after all, it is the load end, no power there, right) and instead finds a hot wire being charged by your generator?

Yeah, he gets electrocuted. And since it is illegal everyplace I know of to hook up a generator to the house wiring without provision for and actual disconnection from the mains, the authorities will track you down and charge YOU with the criminal offense.

SO, FOR GOD'S SAKE (not to mention your own and that lineman), __NEVER__ __EVER__ UNDER ANY CIRCUMSTANCES, __EVER__ FIRE UP THE GENERATOR IN YOUR RV WHILE LEAVING IT PLUGGED INTO SHORE POWER.

Beyond that, even if no lineman gets electrocuted, what happens to your generator when the power does come back on? Odds are good that your generator will be out of sync with the power plant, and you will have instant short circuit, with the little on at your house trying to overpower the big one down at the power station. If you are lucky, circuit breakers will blow before any damage is done. If not so lucky, your generator explodes in flames.

(Yeah, yeah, I know, if the HOUSE transfer switch is thrown, and the house disconnected from the mains, all is well. Similarly, if the OP's motorhome has a transfer switch, he's golden. But the original post showed no evidence of the sophistication of having such a setup. And sure-as-the-lord-made-the-little-green-apples, there will be people reading this thread who AREN'T sophisticated enough to have such a setup and use it.)

Well Scott and Bruce already explained it to better then I probably could have.

Just to go over it-
If no auto transfer - The plug from the rv has to be plugged into the rv to power said rv. So no plug going to house when gen is in use. Fool proof.

If RV does have auto transfer and is plugged into house and residential power is down and you are running gen there will be no back feed to the hose period. Same as Scott said about the house stand by gen..fully automatic.
The gen as to shut down first to get power from the house when power has been restored.

[ScottG]

A side point here..
I have actually seen someone back-feed the electrical service and here's what happened: Nothing.
When he tried to power the entire neighborhood from the feed for his house, the 7.5KV genny just labored down. There's no way it can power all the street lights, and other homes in the area let alone get through the xfmr on the pole.
I'm NOT saying there isn't a danger to utility workers, there certainly would be under the right circumstances.
But if someone tries to back feed the first thing they'll probably run into is loading problems.

[BruceMc]

There are two setups for a generator:
1) Automatic transfer switch
2) No ATS - Manual transfer

In the normal setup (not rednecked/modded/whatever you call it) where there is no ATS, then the shore power cord must be plugged into one of two places:
1) Shore power
2) A receptacle where power is supplied by the generator located in the shore power cord storage location. (or similar)

Therefore, if the shore power cord is plugged into shore power, and the power goes off, starting the genny powers nothing. The user must unplug from shore power and plug it to the generator output receptacle to power the RV.

There is no chance of backfeeding the grid with this setup.

I have an RV that does not have an ATS. Every RV I've seen has an ATS or a receptacle - Automatic or manual power transfer... it is still transferred.

[ScottG]

Capt Storm is correct if:
The transfer switch has isolated the gens output from the shore power plug. There is no issue there and in a home system with a stand by generator (which uses the same transfer switch technology), this is exactly how it works. You don't have to unplug the "house" and there is no NEC code that says you have to as long as you have an approved automatic or manual XFER switch.

If your not using a XFER switch then unplug and stop using whatever cludge was used to connect the genny.

[naturist]

Capt.Storm wrote:
Good thought but yep,you're fine doing that.

NO! Wrong answer!!

YOU MUST UNPLUG THE CAMPER FROM THE HOUSE WIRING WHEN THE GENERATOR IS RUNNING. It is required by law, as well as common sense safety considerations. Somebody could get killed!

REALLY.

Here's the thing, power goes out at your house. Maybe it is because a tree fell on the lines. So what happens when the lineman goes to repair that line, grabs the end that goes to your house (after all, it is the load end, no power there, right) and instead finds a hot wire being charged by your generator?

Yeah, he gets electrocuted. And since it is illegal everyplace I know of to hook up a generator to the house wiring without provision for and actual disconnection from the mains, the authorities will track you down and charge YOU with the criminal offense.

SO, FOR GOD'S SAKE (not to mention your own and that lineman), __NEVER__ __EVER__ UNDER ANY CIRCUMSTANCES, __EVER__ FIRE UP THE GENERATOR IN YOUR RV WHILE LEAVING IT PLUGGED INTO SHORE POWER.

Beyond that, even if no lineman gets electrocuted, what happens to your generator when the power does come back on? Odds are good that your generator will be out of sync with the power plant, and you will have instant short circuit, with the little on at your house trying to overpower the big one down at the power station. If you are lucky, circuit breakers will blow before any damage is done. If not so lucky, your generator explodes in flames.

(Yeah, yeah, I know, if the HOUSE transfer switch is thrown, and the house disconnected from the mains, all is well. Similarly, if the OP's motorhome has a transfer switch, he's golden. But the original post showed no evidence of the sophistication of having such a setup. And sure-as-the-lord-made-the-little-green-apples, there will be people reading this thread who AREN'T sophisticated enough to have such a setup and use it.)

[GrumpyandGrandm]

With all of the above being very accurate they DO NOT RECOMMEND starting the gen while the shore power is energized. If you are goint to exercise the gen as recommended unplug the shore power first.

[j-d]

Probably about as safe as a flight aboard a 777. No MH or ATS manufacturer warns about, or protects against, the Shore Tie cable going "hot" when the genny is running. I suppose some kind of catastrophic failure could let that happen, but like I said, no warnings or provision against it.
Just NEVER NEVER "back feed" the house by making up a double-male cord and connecting a coach outlet to a house outlet. OK to use the RV to keep your home fridge cold, simply run an extension cord inside and plug direct to it.