Need to ground RV power pedestal progress report

[charliem]

As I recall the National Electrical Code (NEC) requires 18" unless under rock or concrete. Used to be you could bury a 30A or less circuit 12" but I didn't see that exception last time I looked.

[FastEddieB]

He just messaged me back - 24" to 36".

[FastEddieB]

OK, Mike Sokol got back to me.

First, it would never, ever have occurred to me that the underground ROMEX I had on hand would be improper for the short run to my 20A outlets, but he replied in response to my photo:

Ed,

So there's three reasons I can think of to replace that short run of underground Romex with the proper cable:

#1)   The plug you've connected it to is probably (almost certainly) not rated for solid wire. It really needs to be stranded wire.

#2)   Solid wire Romex isn't rated for use where I can be continuously flexed. That will eventually cause work-hardening and breakable. Sure it would take thousands of flexes to make that happen, but when it does there can be a real fire hazard.

#3)   The sheath of this Romex cable isn't rated for abrasion, so something rubbing against it will eventually break though the insulation and cause a potential shock hazard.

To be 100% code compliant, this piece of exposed Romex really should be replaced with a length of 12-gauge SOOW rubberized extension cable. At least that's how the latest code is interpreted. It's not expensive and rated for up to 600 volts, plus it's a hard-serivce cable that can withstand abrasion, oil, immersion in water, and flexing at cold temperatures. You might be able to get by with SJOOW (Junior Hard Service Cable) which is similar but rated for up to 300 volts with a thinner jacket. It's likely that using a piece of SJOOW (available for may 50 cents a foot at any Lowe's or Home Depot) would satisfy most any inspector who takes a peak. That piece of exposed Romex wold raise a red flag with any inspector I know and could cause all kinds of other questions to be asked.

You'll want to confirm the continuity of the ground bond on the far end of this run by measuring between the neutral and ground wires. It should measure maybe a volt or two with any substantial load. If it measures 5 to 100 volts, then the ground is floating. If it measures zero volts (with a load) then you have a bootleg ground. But a volt or two (half of the total voltage drop over that length of wire) is what you should expect to measure.

Yes, you can post this on your forum as long as you send me a link so I can confirm you've included all the facts. And please send me a picture of your final solution. 

I replied that I would swap the correct rubberized cable for the ROMEX I used next time I was up.


Secondly, he said this about my original query about a ground rod at the pedestal:

And you can certainly add your own ground rod at the secondary end of your system. That may be required in some localities and would look good to any inspector <who> takes a look.

[DavidM]

While SOOW cable may be suitable for underground direct burial, that is not what the industry uses. They use UF (underground feeder) cable for this purpose. It is available at Home Depot or Lowes for $19 for a 25' roll of 12/2 cable, which is what you need for your 20 amp circuit.

Most codes require it to be buried 18" deep. It is also a good idea to cover the first 6" inches or so with a contrasting sand to warn a future digger that something is there.

David

[FastEddieB]

We were not talking about any of the underground runs, just the final bit connecting the underground ROMEX or wires in conduit to the 20A receptacles on the temp pole.

[DavidM]

OK, sorry I thought this was underground. Yes SOOW would be the right thing for exposed, above ground cabling.

David

[Merlin]

Thanks for posting the info. Sokol's an experienced source for electrical safety in RVs.

Now if you could just find that extra N-G bond in your camper...........

[jmsokol]

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.

Yes, the way this is wired will allow the 30-amp outlet to be powered up, but only with 20 amperes of current available. That's not dangerous and not even a code violation as long as you make it with a +20-amp service" sticker in some locations. The upstream 20-amp circuit breaker will protect the 12-gauge wire run from over-current, so that's perfectly safe. However, 125 ft of wire is a really long run (code calculations are based on 100 ft), so it's doubtful you'll be able to start an air conditioner on that circuit. You'll want to listen carefully when starting the HVAC to make sure it's not going into locked-rotor mode (humming but not starting up) since you can destroy an HVAC compressor pretty quickly with undervoltage.

Mike Sokol
No~Shock~Zone

[FastEddieB]

Thanks! And welcome!

When I was up last time, I tested and the 30A service is wired to be on a different "leg". It would take a jumper between the two screws on the upper left to energize it.

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That would also energize both sides of the 50A breaker. If I went this way I could either disconnect the hot leads out from the 50A breaker or just leave the 50A breaker off and mark it INOP. I had already thought about marking the 30A outlet "20A SERVICE ONLY".

I forgot to check the gauge of the cable in the underground run. From the photo, it looks to me like the runs to the outlets in the cover is 12GA, and the cable coming into the box is clearly larger - 10 GA? I will check next time up.

As an aside, I also painted the ground wire a much brighter green to avoid possible confusion.

Thanks again for your expertise - please don't be a stranger!

[jmsokol]

That would also energize both sides of the 50A breaker. If I went this way I could either disconnect the hot leads out from the 50A breaker or just leave the 50A breaker off and mark it INOP. I had already thought about marking the 30A outlet "20A SERVICE ONLY".

Actually, every dogbone adapter you see with 15/20 to 50 amp converter plugs does a jumper between the two hot legs on the 50-amp side, and connects it to the single hot leg on the 15/20-amp side. So you can make the jumper yourself and save someone from needing an adapter. Same for the 30-amp outlet adapters. Of course, you'll still have only 20 amps available, but if you go over the limit the circuit breaker will trip, so no big deal.

I forgot to check the gauge of the cable in the underground run. From the photo, it looks to me like the runs to the outlets in the cover is 12GA, and the cable coming into the box is clearly larger - 10 GA? I will check next time up.

If it's 10 gauge that's great since that will reduce the voltage drop on 125 of wire significantly. In fact I generally oversize the wire gauge on any run that's going to be over 100 ft, and even for 50 ft runs.

As an aside, I also painted the ground wire a much brighter green to avoid possible confusion.

Just be as obvious as you can be. We generally use green PCV electrical tape.

Mike Sokol
The No~Shock~Zone

[Merlin]

Thanks for joining and posting, Mike.

[charliem]

Actually, every dogbone adapter you see with 15/20 to 50 amp converter plugs does a jumper between the two hot legs on the 50-amp side, and connects it to the single hot leg on the 15/20-amp side.
Mike Sokol
The No~Shock~Zone

Mike,

I know you really didn't mean what you said. A jumper between the two hot legs on the 50A side would be very exciting....for a millisecond or so. The dogbone adapters connect ONE 50A hot to the 15/20/30A socket.

[jmsokol]

Actually, every dogbone adapter you see with 15/20 to 50 amp converter plugs does a jumper between the two hot legs on the 50-amp side, and connects it to the single hot leg on the 15/20-amp side.
Mike Sokol
The No~Shock~Zone

Mike,

I know you really didn't mean what you said. A jumper between the two hot legs on the 50A side would be very exciting....for a millisecond or so. The dogbone adapters connect ONE 50A hot to the 15/20/30A socket.

Actually, I did mean what I said, but let's make sure I'm being clear about what I'm saying. On a 15-amp male to 30-amp female adapter there's one-to-one connections between the hot, neutral and ground contacts. That is, Hot-to-Hot, Neutral-to-Neutral, and Ground-to-Ground. On a 30-amp male to 50-amp female adapter there's a slightly different connection setup. While there's a Ground-to-Ground connection and Neutral-to-Neutral connection from the 30-amp male plug to 50-amp female outlet, there's also a Hot-to-Hot-to-Hot connection from the 30-amp male plug to the 50-amp female outlet. That is, both hot legs of the 50-amp outlet are indeed bonded together and connected to the single hot leg of the 30-amp plug. That being the case, a single 20-amp male plug to 50-amp female outlet does have the two hot legs bonded together on the 50-amp outlet side. Of course, you can't bond the two hot legs together on the incoming power side as that would be a spectacular short as you noted.

I think why there's confusion is that I'm an EE and always talk about power from the source to the load. That is, I start on the end that plugs into the pedestal or home outlet and finish with the end you plug your RV into. So while I will call something a 15 to 30 amp dog-bone adapter, I have noticed that a lot of RV owners talk about adapters the opposite way. That is, you'll call the same thing a 30 to 15 amp adapter to plug your 30-amp RV into a 15-amp outlet in your home. Hard for me to get out of that habit after 50 years of going from power source to load.

Also note that it's hard for me to call any of this an outlet. In the NEC it's referred to as a receptacle, NOT an outlet, even though outlet makes more sense.

So please sound out if what I'm saying is confusing. I'm trying to be as exact as I can while still using as much layman slang as possible. If you need more clarification you'll need to wait until I get back from Paris next week. I have a bunch of diagrams on my home computer I can post later.

[charliem]

OK, I agree. The way I first read it you were adapting between the 50A pedestal mounted receptacle and a 15/20A cable mounted plug from the trailer. 'Nuff said. We EEs are on the same page. Glad to have you on the forum.

BTW, in the world I come from anything above 0dBm is high power 

[jmsokol]

BTW, in the world I come from anything above 0dBm is high power 

How about +4 dBu 

BTW: I might have a sponsor that will allow me do a few seminars about RV electrical safety and hookups at campgrounds on the mid-atlantic coast. Do you guys have any rallies or meets this summer or fall? I'm in Maryland and normally do seminars as far south as SC and as far north as NY. And I go as far west as Ohio and Indiana. Any suggestions?