Electrician Help! Wiring to RV Power Pedestal

[lewster]

See post #5. Again, I would NOT seek advice from any other source but a licensed LOCAL electrician who KNOWS and FOLLOWS your applicable state and local codes.

Any other path is foolish and potentially destructive!!


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center
Lifeline Batteries**Magnum Inverters
541-490-6357

[matthorr]

Originally Posted by nrgtrakr

Not an electrician, but a stationary engineer listening in ...
Wondering why not a 30 or 50 amp box for a 30 amp trailer?
Curious about what the electrician will say about the capacity of the source box and total load.
Guessing 2-2-4-6 (hot-hot-neutral-ground) in conduit - both in the house and underground.
We used nothing but copper when doing additions in hospitals, but I never asked why.

The extra 20A circuit will allow for a heated water hose, for example, or an outside light. The easiest would be to just run to a single 30A receptacle, but that would be the easy way out I figure that the hard part is digging the trench, so I might as well provide for more than I need an not have to go back later.

[matthorr]

Originally Posted by jdalrymple

I am not an licensed electrician, but I too understand electricity.


For 50 amp RV loads, each of the conductors must carry a full 50 amp load. Because none of the appliances are 240 volts, the neutral conductor gauge must equal to the line conductors.

I believe you are on the right track on using romex in the stud walls and splicing to the 2 ga inside an approved box in the crawl space.



We shall see what others say.


Regards,


JD

The NEC does allow for a reduced neutral. BUT... I believe that is under the assumption that each phase will be roughly balanced, so that less than the full current draw will run through the neutral. Looking at the chart, for 4 ga AL the max ampacity (@75C) is 65A. The layout of the pedestal is:
Phase X - 50A + 30A
Phase Y - 50A + 20A
So worst-case is 80A down the neutral (assuming you connect 2 trailers to Phase X, and don't have anything connected to Phase Y).
If you use 2 ga AL, the max ampacity is 95A so it is safe.

*I* would remember to not connect both the 50A and 30A, but the next guy might not know the limitation. So I would have to either put a 60A breaker off the main or get a 2 ga neutral.

[matthorr]

Originally Posted by Hiho Silver

Just wondering about the aluminum,
Lewster. I had a licensed electrician install a pedestal with 50amp on our rural property, aluminum was half the price, and the panel is almost 200' away from the pedestal so the savings was significant. ( can't remember what gauge, I would have to check). Works great, with everything on, 2 a/c's, electric water heater, microwave, and everything else I could turn on at once. I have a surge protector and the voltage is good. Just wondering, am I going to have problems in the future because I used aluminum?


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I know AL has a bad reputation, but it is quite common in service entry (assuming of course that the connectors are rated for AL). I'm comfortable using AL and my checkbook certainly is...

Thanks, Lewster, for the advice on wire size. I'm not sure why the ground wire would need to be equal size, though. It shouldn't carry current long enough to heat up.

I also agree that hiring a licensed electrician is the smart thing to do, but I want to at least understand the requirements. I am very comfortable doing the work, but I do want to be certain the materials are safe.

AL should be safe if the connectors are rated for AL and properly tightened. AL expands and contracts more with temperature (and is more prone to corrosion), but if properly torqued and with modern alloys is safe. Almost all new homes have AL running into them (just not inside house wiring - old AL wiring I believe is almost 100% BAD and needs to be replaced).

[matthorr]

Originally Posted by Al and Missy

I'm not an electrician either, but I have done some NEC work. I believe you need only to size the wire for the highest capacity receptacle, i.e. 50A.

338.12B says USE shall not be used above ground except for transitioning to another cable type in an approved box.

I'm having trouble finding the voltage drop calculations, but I presume that is why you went to #2 as #6 would be good for 50A at 30 degrees C per the ampacity tables.

Al

I am looking first at ampacity (I started looking at the max for the box - 100A, but the NEC limits 2-2-4-6 AL to 90A for this application), but also voltage drop since it is a long run.

[Hiho Silver]

I no nothing about electricity. I had a licensed electrician install a pedestal with a 50 and 30 amp plug. The run from the main panel was almost 200 feet and we used aluminum. This is how it looks, three boxes, one with breakers and the other two have the plugs. Works great. Didn't have an RV pedestal readily available, so took a different route.



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[matthorr]

Originally Posted by israndy

I am surprised you could not find a 30 amp pedestal, they seem to be at MANY campgrounds. If you plan on having people stay in your backyard next to your trailer I can see wiring for 50 amps, but if you are only running 30 amps, it is much easier. Breaker only draws from one side of the panel, no confusing wires.

I think technically if you do wire up the 50 amp you actually need a second run of wire for the 30 amp outlet. If you put a full draw on the 50 and ALSO put a draw on the 30 you would be overcapacity and run your wire hot until the breaker went. Same for the 20/15 amp outlet. If you are ignoring code and never intend to use more than one outlet label it so. There should be a lockout to prevent more than one working, but I don't know of any pedestal that supports a lockout, they just have the extra circuits run.

Aluminum is GREAT. Copper bends easier as it doesn't need to be as thick for the same rating, and it's generally a softer metal. But aluminum is LIGHT, and CHEAP. Don't diss aluminum, it's why there are metal airplanes instead of coated fabric.

-Randy

You can run a single (set of) wires (50A requires 2 hots). The breaker at the main box needs to be sized small enough to prevent over heating the wire (going above its rated ampacity) and large to avoid nuisance trips. It is complicated to calculate what is needed for a whole house (I assume most new houses don't go through detailed calculations - they just use 200A service and say it's more than enough). But, if you add up the amperage all of the circuits in your house, it will be more than the 100, 150, or 200A service because you don't max everything out at once. The important thing is that each breaker is sized to properly protect each gauge of wire.

[markdoane]

Originally Posted by matthorr

*I* would remember to not connect both the 50A and 30A, but the next guy might not know the limitation. So I would have to either put a 60A breaker off the main or get a 2 ga neutral.

Although I really can't imagine a situation where all 50a goes to just the X leg, and it just happens to be the same leg as the 30a plug, why don't you just run the neutral through a 60a breaker?

[matthorr]

Originally Posted by Hiho Silver

Attachment 247216Attachment 247217Attachment 247218Attachment 247219

I no nothing about electricity. I had a licensed electrician install a pedestal with a 50 and 30 amp plug. The run from the main panel was almost 200 feet and we used aluminum. This is how it looks, three boxes, one with breakers and the other two have the plugs. Works great. Didn't have an RV pedestal readily available, so took a different route.



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Nice, that is what mine will have, just all in one box.

[matthorr]

Originally Posted by greghoro

Matthorr - much speculation in assisting you can be put to rest if we knew exactly what pedistal you purchased.

Manufacturer and model, please.


Greg

Siemens TL137UP Talon Temporary Power Outlet Panel Pedestal with a 20, 30, and 50-Amp Receptacle Installed, Unmetered

Off Amazon:

[matthorr]

FYI on costs (from Home Depot):
2-2-4-6 AL USE is $1.79/ft (bundled as mobile home feeder)
2-2-2-6 AL USE is $1.97/ft (buying all 4 wires separately)
2-2-2-4 AL USE is $2.03/ft (same)
2-2-2-2 AL USE is $2.12/ft (same)

They don't have Cu USE wire available in the appropriate gauge, but for comparison 3-3-3-5 Cu SER (not rated for direct burial) is $7.84/ft (I assume USE would be similarly priced, maybe a ~10% premium as separate wires).

So the cost range is about $196 to $862+.

(USE = Underground Service Entry, can be direct buried but must be inside conduit inside the crawlspace/basement
SER = Service Entry R - cannot be buried)

[Aage]

Originally Posted by matthorr

I just added a parking pad to my backyard to store my trailer. I am going to run full hookups out to it (for convenience and so it can be a guesthouse / AirBnB).

My question is to do with the above statement in your first post.

Before buying and installing the necessary wiring, did you talk to your local county/city or whoever it is that approves changes to housing in your area?

I ask this because in many areas, what you are doing would not be permitted. Some places allow storing a trailer but not hooking it up in a permanent fashion, while other do not allow trailers to even be stored on residential property.

However, I have heard of some that allow full service, including sanitary sewers, and in fact are able to approve installations meant for commercial use, such as yours.

An investment such as you are making certainly deserves to be done in a fully legal manner, right?

[matthorr]

Originally Posted by Aage

My question is to do with the above statement in your first post.

Before buying and installing the necessary wiring, did you talk to your local county/city or whoever it is that approves changes to housing in your area?

I ask this because in many areas, what you are doing would not be permitted. Some places allow storing a trailer but not hooking it up in a permanent fashion, while other do not allow trailers to even be stored on residential property.

However, I have heard of some that allow full service, including sanitary sewers, and in fact are able to approve installations meant for commercial use, such as yours.

An investment such as you are making certainly deserves to be done in a fully legal manner, right?

Yes, here it is OK. My last house, no because of HOA rules (unless it is totally hidden from view).

[greghoro]

Originally Posted by matthorr

Siemens TL137UP Talon Temporary Power Outlet Panel Pedestal with a 20, 30, and 50-Amp Receptacle Installed, Unmetered

This uses a two lugged internal power distribution scheme to connect the outlets through the protecting circuit breakers. Each of the hot incoming wires is connected to one lug.

The 50A outlet uses a double pole circuit breaker (connects to both lugs) to supply power to each of the two hot legs of the outlet while the 30A and 20A outlet circuit breakers are on lugs opposite each other. This means you have to plan for a potential maximum load of 80A (50A + 30A) if all three outlets are powered.

There is no way for this device to disable an outlet when another outlet is used. The only way to disable an outlet is to physically remove its circuit breaker or to remove its feed wire from the circuit breaker.


Greg

[israndy]

That sounds easier than I thought. It is wired in such a way that you just put it downstream of a big breaker off your main panel and it will work correctly. No need to prevent an outlet from working as you brought enough power for all.

Oh, and the 50 amp draws 25 from each side so it's 25 + 30 on x circuit and the other half 25 + 20 on the y circuit.

I am wiring up an electric car charger and forget that though RVs take 220 in, they only use 120 volts at a time, like a real house. Except maybe electric stoves or water heaters, can't think of any examples of those in an RV though.

Car chargers only use 220 so no need for that neutral wire.

-Randy

[markdoane]

Originally Posted by israndy

Oh, and the 50 amp draws 25 from each side so it's 25 + 30 on x circuit and the other half 25 + 20 on the y circuit.

-Randy

The NEC requires that you provide 9600 voltamperes (80a x 120 v) for a single 50a/30a/20a pedestal, so I think Matt and Greg already had the right answer.

[matthorr]

Originally Posted by israndy

Oh, and the 50 amp draws 25 from each side so it's 25 + 30 on x circuit and the other half 25 + 20 on the y circuit.
-Randy

The 50A outlet actually supplies 50A + 50A at 120V for a total of 100A. At 240V, it provides only 50A. I'm not sure what the RVs use inside.

[matthorr]

So, my final analysis is to use a 80A double-pole circuit breaker at the main box. For wiring, 2/0 Al for the two hots and neutral. The ground will be 4 gauge. I'll run individual wires - probably easier to handle than the bundled mobile home feeder, anyway. The price for wire almost doubles but the extra $220 is not too bad in the big picture.

This provides plenty of extra worst-case margin so I won't exceed the ampacity of any wire and I also will be able to use all of the power at the pedestal. I can't fit another trailer in the backyard, but if someone wants to buy me a new Land Yacht or International CCD 27FB with 50A service for two ducted ACs (Oyster Ultraleather, please), I want to be prepared

[matthorr]

One more question - since I need to order the wire pre-cut, how much extra should I order? Any rules of thumb?

[markdoane]

I wouldn't run the aluminum inside the dwelling, so I would just measure the trench length and add 7 feet at each end (18 inches deep + 48" above ground + 18" in the box).
I would use copper in the crawl space, but you're the homeowner.

And I thought we were using #2 AWG, not 2/0?