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Are Separate Plugs For Generator & Shore Power Essential or Optional?

aaron_c

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Jun 18, 2020
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I finished reading through my EVO 2224 Invterter/Charger manual and I see that it has separate terminals for both shore power and generator power.

I'm confused because I thought most RV's just had the one male outlet on the side of the RV that's used for charging the batteries. But this makes it look like I'd need to wire up two external male receptacles, one for shore power and one for gen power. And I guess I'd also have to be very careful never to confuse the two.

I only plan to use the generator as an alternative to shore power and would never need to have them both plugged in at once. So for simplicity sake, it would make things easier for me if I only had to have the one plug on the outside of the trailer, and then I could choose to plug in either the generator or shore power as the need arose.

However I'm not sure if this is something I can do safely. Will using the shore power connections to the inverter for both shore and gen power be unsafe? Will it mess with the ground switching? Does it depend on the inverter in question and should I check with the manufacturer?

Thanks!
 
Depends. My RV has a single umbilical connected to an ATS (automatic transfer switch). The ATS automatically switches between shore and genny to feed the AC panel. It has a preference for grid over genny. Some smaller RVs have a panel connected umbilical that gets plugged into the generator or shore power.

An EVO 2224 is wired for a grid connected system with generator backup eliminating the need for an ATS (should have one internally).

How you do currently switch between shore and genny?
 
Depends. My RV has a single umbilical connected to an ATS (automatic transfer switch). The ATS automatically switches between shore and genny to feed the AC panel. It has a preference for grid over genny. Some smaller RVs have a panel connected umbilical that gets plugged into the generator or shore power.

An EVO 2224 is wired for a grid connected system with generator backup eliminating the need for an ATS (should have one internally).

How you do currently switch between shore and genny?
I'm setting this up from scratch, so currently I plug everything into my truck's cigarette lighter port ;)

I understand that the EVO has an internal ATS, I'm just wondering whether it's essential that I have a separate external receptacle for the generator and the shore power. The EVO is wired for that, but I'm not clear whether that's just optional, like if you want to set up somewhere long-term and want to have your generator ready to hop on whenever shore power gets disrupted.
 
I think there are 2 different use cases for how you might wire it depending on whether your idea of a generator for your RV is a box on the ground that you plug your RV into, or if your RV has a generator built in that has the potential to be actively producing power at the same time that you are plugged into shore power.
Sometime it helps to envision how the EVO might be used in the context of a backup power source for a home. If the grid is up and running, it just passes through grid power and keeps the batteries charged. If the grid drops, the EVO picks up the AC load without missing a beat and draws from the batteries. If the grid is off long enough that the batteries get low, the EVO starts the generator and switches over to that as a source of AC power to power the home and recharge the batteries.
In an RV application, it could be used the same way, or you may have an external generator which would be very unlikely to be remotely controllable by the EVO, in which case, I would be most likely to wire it as if you had no generator and just use the same plug for shore power or generator. The generator in this case is not a controllable 3rd source of power, it is just effectively an alternative version of shore power.
 
It is very desirable to have to unplug shore before using generator and the other way. Sometimes, not always, the floating neutral in the generator will cause problems with some, not all, clean current protective devices. Mike Sokol covers some of it on RVtravel.com here is one of his links. Be sure you understand what he is saying before doing what he says. https://www.rvtravel.com/rv-electricity-companion-bonding-plug/
 
I think there are 2 different use cases for how you might wire it depending on whether your idea of a generator for your RV is a box on the ground that you plug your RV into, or if your RV has a generator built in that has the potential to be actively producing power at the same time that you are plugged into shore power.
Definitely the former, and it wouldn't be used while I was plugged into shore power. And I should have said, this is for a mobile application.
The generator in this case is not a controllable 3rd source of power, it is just effectively an alternative version of shore power.
Thanks, that's kind of what I'm hoping for. Except shore power is (ideally) connected to earth ground, whereas a generator that I store in my truck wouldn't be...oh, ok, I'm starting to understand this differently. Tell me if this is right:

So with shore power we're using earth ground. That's great, works well with automatic ground switching because if we didn't switch grounds then we'd have two grounds...which causes electrical interference...and also if the 120V line was grounded to the chassis and a hot wire electrified the chassis (because the hot wire came into contact with something it shouldn't) then someone touching the actual earth and the RV would get 120V going through them.

Also maybe there's some minor protection from lightning from having your system connected to earth ground?

With the generator, which isn't connected to the earth ground, we'd be similarly protected from a hot wire touching the chassis or the other hot wire or whatever...I think. We get protected from the hot wire touching the chassis, because thanks to ground switching that current will try to return via the ground wire in the 120V cord. That'll blow the breaker and all will hopefully be well...though honestly I have no idea if the breaker would blow quickly enough to protect the generator itself. Still, better to lose a generator than one's life.

Is that right?

And if it is right...bonus question...how is it that a 120V AC breaker just has to go on one of the lines? Why wouldn't we need a double breaker (as is used with 240V systems)? Because although the three cables for AC power are labeled neutral, ground, and...line I think....the two non-ground wires alternate being the "hot" wire. Right? So if one of them was cut the current, when it was pushed through the not cut one, would try to return via ground. But what if the one that was cut was the one with the breaker on it? Wouldn't that be a problem?
 
It is very desirable to have to unplug shore before using generator and the other way. Sometimes, not always, the floating neutral in the generator will cause problems with some, not all, clean current protective devices. Mike Sokol covers some of it on RVtravel.com here is one of his links. Be sure you understand what he is saying before doing what he says. https://www.rvtravel.com/rv-electricity-companion-bonding-plug/
Oh, very interesting.

So if I understand him correctly, he's saying that some generators don't bond the neutral and ground lines in the generator. The bonding of those two lines in the generator (at the source of the power) would allow errant current to return to the generator via the ground line (which is important for safety when dealing with voltage high enough to kill someone). But beyond that, it will also allow some of the devices that do automatic ground switching to correctly detect that you've hooked up to a generator where the neutral and ground have been bonded, and that will allow it to switch grounds to the neutral-ground bond in the generator.

But presumably this only matters in generators where the neutral and ground are not bonded internally. Right? And why wouldn't a generator bond the neutral and ground lines? Oh....maybe because they want to give you the option of connecting the generator ground to earth ground (like in a residential application)?

Am I getting this right?
 
In a mobile application. There is only one condition the generator is to be connected to earth ground. That is if the generator is suppling power to more than one location. Such as an emergency generator for two or more users.
 
In a mobile application. There is only one condition the generator is to be connected to earth ground. That is if the generator is suppling power to more than one location. Such as an emergency generator for two or more users.
Does this mean that in spite of the fact that my inverter/generator has one set of terminals for a generator and one set of terminals for shore power, I can just wire up the shore power terminals and then plug either shore power or my generator into that receptacle? And I can just not wire up the generator terminals?
 
You could hook up all, none, one or the other and even flip them around if you like.

The presence of two connections is a feature, not a requirement. The unit will accept AC-in on either line, so your proposal is fine.
 
Shore power is from a grid tied to a power company. A inverter generator has AC outlets that supply usually 120 volt AC current. That is not "shore power" as it commonly understood. With a RV, the rv shore line could be plugged into the generator outlet. That would insure both generator and shore power is not connected at the same time. = disaster. Some if not all inverter generators also have a 12 dc outlet. Not many amperes are available from that.
If you are talking about one of those batteries w/ inverter in a box that are mislabeled "generator" I apologize.
Inverter generator, = https://www.amazon.com/Honda-2200-W...ocphy=9058691&hvtargid=pla-436981178859&psc=1
 
Shore power is from a grid tied to a power company. A inverter generator has AC outlets that supply usually 120 volt AC current. That is not "shore power" as it commonly understood. With a RV, the rv shore line could be plugged into the generator outlet. That would insure both generator and shore power is not connected at the same time. = disaster. Some if not all inverter generators also have a 12 dc outlet. Not many amperes are available from that.
If you are talking about one of those batteries w/ inverter in a box that are mislabeled "generator" I apologize.
Inverter generator, = https://www.amazon.com/Honda-2200-W...ocphy=9058691&hvtargid=pla-436981178859&psc=1

Hah, that mislabeling always has annoyed me. In a way, a battery is the opposite of a generator....

I didn't realize I could charge my rig by plugging shore power into one of the 120V sockets in my generator. Er...if I can do that. I guess I'd need a male-to-male adapter, and I gather those are not actually legal for safety reasons.

Anyhow, thanks. I think I'll just have the one receptacle on my RV for plugging into either shore or gen power. Since it seems like I don't need separate lines for those sources unless I want to have separate lines to my inverter/charger then I'll opt for the simpler solution.
 
That is what I was saying. Either plug into the grid outlet or the generator outlet using the same cord from the RV. DO NOT plug the shore power into the generator outlets! Avoid like a timber-rattler any cord with a male plug on each end.
 
That is what I was saying. Either plug into the grid outlet or the generator outlet using the same cord from the RV. DO NOT plug the shore power into the generator outlets! Avoid like a timber-rattler any cord with a male plug on each end.
Oh.... ok, gotcha. Thanks Zil.
 
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