Chassis is shocking us when connected to ungrounded shore

[Zil]

Actually, I had wondered about something similar for things like the home brew solar generators on hand trucks and the like. Could you just have a metal spike with the ground wire? Stick it in the dirt once you place your cart and step on it to sink it in? It's a ground, right?

There are different code requirements for some generator installations. But read what I think of "short stubby ground pins" in post 15 and 20.

 

[Zil]

I copied this from Mike Sokol a recognized expert on safe electrical systems. He is talking about a 6 or 8 foot rod driven into the ground, not one you step into the ground. Stay alive, mates.
"There is an 8-gauge copper wire on the right side of the enclosure that goes down to a grounding rod that’s not in the picture. However, that DOES NOT ground the pedestal or your RV. As I’ve written dozens of times, that grounding rod is really there to help a lightning strike find its way deep into the earth before it can cause trouble. Because a grounding rod will typically have an earth impedance around 100 ohms in dry soil, it can never carry enough fault current to trip a circuit breaker if a short circuit occurs inside of your RV.

And without the ability to trip (clear) a circuit breaker rapidly during a shore-circuit event, your RV can easily develop a hot-skin potential of 40, 80 or even 120 volts. And touching anything metal on your RV while in contact with the wet ground can be deadly."

 

[slipperysam]

At a very minimum, a responsible RVer checks a campground outlet with a 3-light tester before using it. As noted above, an EMS automates this process and also verifies the quality of the power. In theory a GFCI would protect you, but I would not advise taking the risk on theory. I do however advocate plugging an RV into a GFCI outlet whenever possible because it can give an early warning of failures. It's fairly common for failing water heater and refrig heating elements to have leakage to ground, and once it starts it's not going to get any better. But any electrical consumer can have faulty leakage to hot or ground.

As far as the 5 volt difference to earth ground when plugged into a grounded outlet goes, you're right that it in theory it should be zero difference. In reality different earth points can be at different potentials. I'm a bit surprised by the difference being 5 volts and would at least make an attempt to see why it's that large a difference. If everything in the bus was perfectly balanced and insulated, the ungrounded chassis would float at the midpoint between the hot and neutral voltages. In reality they tend to float below the midpoint, if for no other reason that there is likely a little resistive leakage through the tires to earth ground, and a capacitive coupling between the chassis and earth ground. I measured my former 5th wheel and current small motorhome for this and if ungrounded they both floated at about 40 volts. If you're parked near a power line, the ungrounded chassis could be really hot, voltage wise. I once visited somebody whose house backed up to a very high voltage transmission line. He could hold up a fluorescent tube from his back deck, and when parallel to the line, the darn thing lit up dimly.

I see, thank you for your help and additional context. This is all new to me, including RVing, so every bit helps. Took your advice and got a hold of a Progressive Industries 50A tester to avoid this situation in the future. Plugged it into the troublesome outlet (with my 15A - 30A, 30A - 50A adapters in place) and lo and behold, it showed a red warning that neutral and hot were reversed!

It sounds like some of the comments above also figured this was the case. The difference between chassis and earth makes a lot more sense now.

Serious advice.....

Run a 3 wire 10 guage service to a dedicated outlet for the R.V. Use a NEMA TT-30 socket and connector to plug in your bus to shore power. This TT-30 connector is very specifically designed for travel trailers and RV’s

This is exactly how all marketable R.V.’s are wired to code.....and yes, you do need to be “code” even if it is not a building.......your are living in it.....

I'm just renting a place out while I build my mobile home. We move out at the end of the week, and then will be living on the road. If I settle down, yes, of course I'll get a dedicated 30A or probably 50A inlet installed on my property. As far as the RV goes, I can't claim knowledge of the entire code, but I have closely followed many other experienced people, including advice from people on this forum. I feel pretty confident that the bus itself is set up well. It's the exterior outlets that I'm plugging into that are the unknown for me.

Ya, there’s I think three things going on and polarity was the first thing that crossed my mind.

There’s more to it than that.
So the neutral and bare/green are not connected in the bus in any way, right?
And you have a way of disconnecting/transferring Hot, Neutral, and Earth/green from the RV cord to onboard inverter, right?

unrelated issue but a lot of good resources for understanding in the later pages concerning ‘grounding.’

They are not connected in the bus (however, my understanding is that the Multiplus will indeed internally connect neutral and green when not connected to shore power). I don't understand the second question. I have a 50A RV inlet, and that is directly wired to the AC-IN of the Multiplus 24V 3000VA (only one of the hot legs; the other one isn't used and just doesn't have a wire between the inlet and the Multiplus). I questioned the utility of an inline breaker between the shore inlet and AC-IN. I do have a small Progressive Industries surge protector though, and I simply set the AC-IN current limit on the Multiplus based on the shore power that is available.

However after the many responses on this thread (thanks for your help everyone) I think I will go ahead and get a full EMS. Seems like money well spent.

 

[Alloy]

I see, thank you for your help and additional context. This is all new to me, including RVing, so every bit helps. Took your advice and got a hold of a Progressive Industries 50A tester to avoid this situation in the future. Plugged it into the troublesome outlet (with my 15A - 30A, 30A - 50A adapters in place) and lo and behold, it showed a red warning that neutral and hot were reversed!

It sounds like some of the comments above also figured this was the case. The difference between chassis and earth makes a lot more sense now.


I'm just renting a place out while I build my mobile home. We move out at the end of the week, and then will be living on the road. If I settle down, yes, of course I'll get a dedicated 30A or probably 50A inlet installed on my property. As far as the RV goes, I can't claim knowledge of the entire code, but I have closely followed many other experienced people, including advice from people on this forum. I feel pretty confident that the bus itself is set up well. It's the exterior outlets that I'm plugging into that are the unknown for me.


They are not connected in the bus (however, my understanding is that the Multiplus will indeed internally connect neutral and green when not connected to shore power). I don't understand the second question. I have a 50A RV inlet, and that is directly wired to the AC-IN of the Multiplus 24V 3000VA (only one of the hot legs; the other one isn't used and just doesn't have a wire between the inlet and the Multiplus). I questioned the utility of an inline breaker between the shore inlet and AC-IN. I do have a small Progressive Industries surge protector though, and I simply set the AC-IN current limit on the Multiplus based on the shore power that is available.

However after the many responses on this thread (thanks for your help everyone) I think I will go ahead and get a full EMS. Seems like money well spent.

GFCIs are needed on bath, kitchen and outdoor receptacles and it's not bad having some AFCIs

 

[HRTKD]

However after the many responses on this thread (thanks for your help everyone) I think I will go ahead and get a full EMS. Seems like money well spent.

Note that there are internal and external EMS devices. I have an external. The internal devices are hard wired inside the trailer. Set it and forget it, more or less. The external ones get plugged into the campground pedestal. The warning I've heard about the external ones is that they tend to disappear (get stolen). Storing them is not a lot of fun. Mine takes up a lot of room in my cabinet. There are times I wish I had installed an internal one.

 

[12VoltInstalls]

They are not connected in the bus (however, my understanding is that the Multiplus will indeed internally connect neutral and green when not connected to shore power). I don't understand the second question. I have a 50A RV inlet, and that is directly wired to the AC-IN of the Multiplus 24V 3000VA

Question 1 answer: good. Correct

2nd Question: multiplus sounds correct also

showed a red warning that neutral and hot were reversed!

and so it it’s fine in the bus on the multiplus output then, correct? I’m assuming so.

 

[Alloy]

Note that there are internal and external EMS devices. I have an external. The internal devices are hard wired inside the trailer. Set it and forget it, more or less. The external ones get plugged into the campground pedestal. The warning I've heard about the external ones is that they tend to disappear (get stolen). Storing them is not a lot of fun. Mine takes up a lot of room in my cabinet. There are times I wish I had installed an internal one.

If an internal EMS is used with a pass through inverter the EMS needs some modification.

 

[Johnson]

I see some comments about putting ground rod near the RV. Even if you could get a proper ground, this would be a bad idea. Currently grounding is done at the transformer and again in the house, this is done not because it is the best way, but because it is the cheapest way.

If you get a shock at the RV you have improper ground in the house and or RV. And there is a short circuit between a phase and ground which won't trip because grounding is inadequate. You really need to get a licensed electrician to have a look at this and be prepared to pay for fixing the problems.

It might be easier to think about grounding as introducing a known fault condition (short between neutral and ground) in order to be able to take emergency action in case of a second fault condition.

Please get a licensed electrician to clean up the mess.

 

[12VoltInstalls]

there is a short circuit between a phase and ground which won't trip because grounding is inadequate.

Please get a licensed electrician to clean up the mess.

They already proved it was not their setup I believe. It was an externally introduced problem. They were able to find it with a tester.
I don’t believe they have a mess to clean up?

 

[Hedges]

Swapped Line and Neutral shouldn't electrify the chassis, unless RV bonds neutral to ground even when plugged into shore power. If so, that's an issue, not really a mess, to clean up.

 

[Johnson]

They already proved it was not their setup I believe. It was an externally introduced problem. They were able to find it with a tester.

I don’t believe they have a mess to clean up?

You are right that the problem starts at the house, it starts even before that, when we decided to grond the neutral in multiple places, but that is a discussion that should be left to engineers.

The problem is how do you wire movable systems so that they are safe, people here have suggested isolating transformers and even not carrying the earth into the vehicle itself. You can do that with an isolating transformer and ground fault detection. However there is no perfect solution, vibration could create problems in the future. The multiplus connects ground when it detects shore power, something you would want in normal conditions. But you should never have to rely on an outlet (you have no control over) being wired correctly to be safe in your mobile home.

 

[Zil]

There is a mess to clean-up! Even with the white and black wire on the correct side of a two hole outlet there is a very real danger of being killed or injured by a hot skin condition of the RV. The only solution is installing the proper outlet, wired properly, with a earth ground (green) circuit back to the utility grid entry panel.

 

[Hedges]

The problem is how do you wire movable systems so that they are safe, ... But you should never have to rely on an outlet (you have no control over) being wired correctly to be safe in your mobile home.

 

[12VoltInstalls]

hot skin condition of the RV. The only solution is installing the proper outlet, wired properly, with a earth ground (green) circuit back to the utility grid entry panel.

I thought they had said that was a temporary connection they are not going to located at again, and going forward they know now to test every plug-in before connecting. Maybe I mixed threads?

 

[Zil]

I am responding to some links after the OP. Guess I should re read stuff first. I am relieved they are no longer plugged into that outlet. And I hope never into another two prong outlet.

 

[slipperysam]

To follow up, that's correct, we rented a house for just a year to do this bus build and I was plugging the multiplus into the exterior outlet of this house once we finished the electrical system. We move out tomorrow and will be on the road from now on! And I have my progressive industries tester to use moving forward. Long term I likely will get a hardwired EMS for peace of mind.