Need to ground RV power pedestal progress report

[FastEddieB]

We're making steady, if slow, progress getting our RV site set up at our airstrip property in Lenoir City, TN.

We got our temp pole inspected and powered up:



(water is also running to the frostproof spigot)

This setups for just until we have our hangar built - at that point the wiring will run from the hangar panel back to the RV pedestals at whatever amperage we choose.

The utility company would not approve more than two 20A circuits, so that's what we're having to live with for now. The box cannot be modified or hard-wired.

The plug seen is underground ROMEX running to lights and outlets to my shed.

Yesterday I installed a junction box and a similar 20A plug to connect to the wiring run into the underground conduit seen in the above photo.

Got the RV panel wired yesterday:





Questions...

1) Would it enhance safety to install a ground rod at the pedestal?

2) It appears as though the 30A outlet will be "hot" if I throw the breaker. I know more than a 30A draw will pop the breaker at the temp pole, but otherwise is it feasible to just plug my 30A cable into that? I'm hoping the gauge of the wire and relatively short (125') run may allow us to run the air conditioning. If not we can always power up our generator in the heat of the day.

Thoughts?

As an aside, we got the gravel down:



Next priority is getting topsoil and grass seed down - the ungraveled areas turn into a muddy mess in the rain!

[DavidM]

Eddie:

The power company installed a ground rod at your incoming power panel, right? Then that is the only ground you should have. The NEC requires one ground at the power source and only one ground to prevent ground loops.

I had a hard time following your description, but I think you will be able to run A/C from your new power supply as long as the wire size is big enough. I suspect it is at least 10 gauge which should work ok. A two hundred fifty foot round trip with 10 gauge and 20 amps results in a bit more than 5 volts drop. High but usable. #8 would be better.

David

[FastEddieB]

Thanks!

Yes, there's a ground rod at the temp pole.

So, one at the pedestal is actually a bad idea? I ask because I installed one at the pedestal at our N GA home, thinking "belt and suspenders". It's about 225' from the main panel. There we used 4ga aluminum wire.

Sorry, not sure of the wire gauge on the property, though you can get an idea from the open panel photo. I'd guess 8ga - it's larger than the wires running from the buss to the 20A and 30A outlets, for comparison purposes. I'll verify next time up!

[Merlin]

Yes, a second ground is a bad idea.

It looks like you've got 240AC at 50 amps in your RV box. Wow! What's that for?

To your previous question; yes, you can power your new RV box with your temp 20 amp supply. The temp box breakers are the controlling limiter, but it's fine to use that arrangement. If you draw more than 20 amps, the breaker will flip, but no big deal.

[FastEddieB]

Yes, a second ground is a bad idea.

Then maybe I should disconnect the one I put in at home?

Can you clarify why it's a bad idea? On the surface it seemed like a safety measure.

It looks like you've got 240AC at 50 amps in your RV box. Wow! What's that for?

Nothing, right now. It's just how the RV boxes came configured.

Ultimately, we'll have two pedestals. The idea was to have 50A available in case someone with a large RV that required it were to visit.

This seems to be how they're wired:



Seems like we'd have to pull a second hot lead for that to work.

[DavidM]

Eddie:

The National Electric Code requires one and only one ground located at the power source, which in your case is the power company supplied power panel. You will not be in compliance if you install another ground rod downstream of that one. 'Nuff said.

Now if you just added a second ground at a secondary panel AND DID NOT TIE THE NEUTRALS TO IT, and just made it another ground in parallel with the primary one, then I can't see anything particularly bad about that practice. But why do it if the NEC says not to?

Some years ago I installed an outdoor hot tub at the back of our house and the main panel was in the front. The NEC requires a disconnect and a GFCI within 10' of the hot tub. So it was a similar situation to yours and I did not install a separate ground rod. The building inspector approved that installation.

David

[Merlin]

Here is the reason for one, and only one, ground point in an electrical system:

"The common ground point—installed in the service disconnect panel—is connected via a grounding electrode conductor to the common ground reference, such as a ground rod. This connection to earth is made at only one point in each electrical system; otherwise, parallel paths will exist for the currents to flow. These parallel current paths would represent a safety hazard and are not allowed in installations wired per the NEC/CEC."

Also, I see now that the big 240VAC/50A breaker in the RV panel is not wired up yet (although one leg of it may be hot per the photo, so be careful). If you ever have "friends" camping there that need that kind of power, be prepared for an increase in your electric bill!

[charliem]

My Saturday morning two cents' worth:

It seems the operative distinction is whether the added ground rod is connected to the system neutral. There must be only one intentional N-G connection. In any installation involving long wire runs there will be a voltage developed between the system ground point and the neutral at the remote point. Any appliances connected to that neutral will develop a voltage on the case due to capacitive and/or other high impedance paths. Eliminating these voltages, and accidental shorts, is the purpose of the safety ground. Connecting the trailer frame to the system safety ground, i.e. the ground wire in the 3 wire service line as it should be, will eliminate most but maybe not all of this voltage. Connecting the trailer frame, NOT the system neutral,  to an added ground stake will further reduce the potential referenced to the physical ground at the specific trailer location. This is OK. Recognize that additional parallel ground paths between the trailer frame and earth ground are impossible to eliminate, but they may be through leveling jacks, the tongue jack, or even people. Bottom line: If voltage exists between the trailer and local ground, first verify the system safety ground is intact and no direct N-G connection exists in the trailer or local power pedestal. If OK, an additional ground stake is appropriate if not connected to system neutral.

[Paul]

Eddie you have a nice property! Before going seasonal in a campground I had considered buying a property instead. I might do it sometime

[FastEddieB]

Thanks for all the input!

Who knew health insurance electricity could be so complicated?

To be clear, I think I understand that ground and neutral should not be bonded anywhere but at the main panel/source. The question is just: does an earth ground at an RV pedestal benefit in any way from having its own earth ground?

I did a Google search to try to find a clear explanation and the amount of conflicting information is astounding! And much of it seems quite authoritative, listing and quoting pertinent NEC codes. It seems like a lot depends on definitions of things such as "structure" and "branch". It also seems like the need for an earth ground at pedestals may vary with location, and maybe even the inspector involved.

I ended up on Mke Sokols's NoShockZone page: http://noshockzone.org

Others have recommended him and his site as a "go to" source for all things electrical. I'm going to email him with my exact situation and see what his take is. I'll post his answer here (with permission, of course).

I don't want to seem argumentative or ungrateful for the advice so far, and I really do appreciate it.

[Merlin]

Good move. I hope he will help out.

[FastEddieB]

Good move. I hope he will help out.

He emailed me from Rotterdam(!) and said he'd try to answer my question tomorrow.

I'll keep you guys updated.

For those interested, the text of my email to him:

Here are the particulars:

We bought some property on an airstrip in Lenoir City, TN. We've made a fenced area to park our 21' CampLite travel trailer in. The idea is to give us a base of operations while a hangar and efficiency apartment are built over the next year or so.

The utility company so far will only allow a temp pole to have two 20A circuits. We had one installed and it passed inspection and is powered up:

<IMG_5083.jpeg>

That ROMEX is running underground to a nearby shed. The conduit is running about 125' to where we've put an RV pedestal. I have since wired a 20A plug and attached its leads to the three pulled wires in a waterproof junction box. The temp pole has an earth ground.

I wired the other end thusly:

<IMG_5095.jpeg><IMG_5097.jpeg>

I think I know enough to leave the bare copper wire on the right unbonded to neutral. For now we can live with 20A service to our trailer, since the utility company forbids any modifications to the temp pole once installed and inspected. They've apparently had issues with customers getting larger capacity feeds - for boats mainly - and then using it as a semi-permanent installation. Ultimately, once the hangar is built, 100A service will run from the transformer to a main panel and meter at the hangar and then run from there back to the RV pedestals (there will ultimately be two) using the existing conduit and wire. I think I see that if we ever wanted to use the 50A outlet, a fourth wire would have to be pulled.

Anyway, my inclination was to install a ground rod at the RV pedestal to provide some additional level of safety if the ground from the temp pole was ever compromised. Or maybe just lightning protection. Others have suggested that's either unnecessary or a bad idea in general.

Would you mind sharing your thoughts, and would you mind me posting them to the forum?

As an aside, I have a similar setup at my N GA home, but using 4GA aluminum wire over a 225' run. I did install a ground rod at the RV panel there.

As a further  aside, I have had a "hot skin" of a full 110V once, due to a mis-wired pump house outlet combined with accidentally shorted ground and neutral circuits on my trailer. So count me in the camp of those to whom it has happened! It's especially scary when a grandchild asks, "Why is the trailer shocking me?"

Thanks in advance, and enjoy your Sunday!

Fast Eddie

[FastEddieB]

As an aside, as I wait for a fuller response from Mike, here's the final 20A outlet to underground wiring interface at my temp pole:



We turn off the breakers and unplug when we leave and padlock the panel.

[Merlin]

When permanently burying wiring in that plastic conduit, how deep did you have to go with the trench?

[FastEddieB]

When permanently burying wiring in that plastic conduit, how deep did you have to go with the trench?

I wasn't there, so I'm not sure.

I'll ask.