rv park service and wire to pedestal??

[justwondering]

Looking at a little RV park. 125 spots ,owner wants 50amp receps at each. 551.73 reduces my service feeders to 41% Service is in a building in the middle of the property. I want to bring a feeder wire to a j-box and tap off to 5 or 6 lots. I can reduce the feeder wire right? How? From the tap to the pedestal Ill run #8?. Anyone know a manufacturer for feed through combo 50/30 recepts for RV let me know.

 

[justwondering]

Re: rv park service and wire to pedestal??

Answering my own question?? If i feed in and out (in a line)of say 10, 50 amp pedestals for 10 rv sites. I could run one 4/0 thhn set of conductors, right?

 

[active1]

Re: rv park service and wire to pedestal??

I think milbank makes these RV pedistals. I did some this year and the park provided the pedistals. They had some RV park mail order place send them out for around $100 each. I don't think they were milbank. They had 1 30 A 120v rec and 1 20a 120 v gfi. It had a 30 and 20 Single pole breaker. It had double lugs to feed in and out.

We were changing an existing set up. It was set up as 2 30 amp pedistals on one 60 amp breaker. The pedistals had 1 rod each connected together because no ground was run.

I don't know about derating the pedistals 41% and having 10 on 1 line. If there was a strong load there might be a lot of unhappy campers.

It may not be a problem with the 50 a pedistal but I know there are illegal plug addapers sold to RVers to change from a 20a to 50a or 30a to 50a.

Don't forget to factor voltage drop.

I don't think you can tap off with smaller wire than the breaker allows with out over current protection. But I can't remember the tap rule right now.


Happy trenching,
Tom

 

[iwire]

Re: rv park service and wire to pedestal??

Originally posted by active1:
The pedistals had 1 rod each connected together because no ground was run.

That is very unsafe, was this job inspected?

 

[iwire]

Re: rv park service and wire to pedestal??

Originally posted by justwondering:
If i feed in and out (in a line)of say 10, 50 amp pedestals for 10 rv sites. I could run one 4/0 thhn set of conductors, right?

Looking at all of 551.73 that way of doing it looks acceptable. However I am not sure about your wire size. I am guessing you mean 4/0 aluminum?

10 sites 9600 VA = 400 amps

400 amps x .5 demand factor (Table 551.73) = 200 amps.

To me this is at least 3/0 copper or 250 aluminum you can not use the 90 C column.

4/0 AL is rated 180 amps @ 75 C you can not use 240.4(B) to round up to a 200 amp breaker because the the load is 200 amps.

I do not know if this load is considered continuous or not.

If it is continuous load the 10 sites would need to be on a 250 amp breaker which would move the conductors to at least 4/0 copper or 300 aluminum.

I did notice a FPN right under 551.73(C)

FPN:These demand factors may be inadequate in areas of extreme hot or cold temperature with loaded circuits for heating or air conditioning.

There is also this FPN under 551.73(D)

FPNue to the long circuit lengths typical in most recreational vehicle parks, feeder conductor sizes found in the ampacity tables of Article 310 may be inadequate to maintain the voltage regulation suggested in the fine print note to 210.19. Total circuit voltage drop is a sum of the voltage drops of each serial circuit segment, where the load for each segment is calculated using the load that segment sees and the demand factors of 551.73(A).

Not enforceable but something to think about.

It might be worth while to get an engineer involved with a project of this size and costs.

A service that looks to be 2500 Amps, 125 sites to feed 9600 VA to.

Did the power company stick with a 400 amp service recommendation? That is about 3 amps per site.

Good luck it sounds like it could be a nice job, Bob

 

[hurk27]

Re: rv park service and wire to pedestal??

By justwondering: I could run one 4/0 thhn set of conductors

Nope
THHN is not a wet location wiring method.
Even if these cables are run in a raceway it must have a "W" in the sufix.
I take it these cables are running to the pedestals underground?

 

[active1]

Re: rv park service and wire to pedestal??

Maybe I should clairify about the grounds. The pedistals had a nutral ground conductor. This was bonded to the equipment ground and ground rods. Each pedistal is treated like a seperate structure.

I just mean if I was doing the park from the start I would have an equipment ground connecting to all locations from the main service.

Tom

 

[hurk27]

Re: rv park service and wire to pedestal??

By active1: The pedestals had a neutral ground conductor. This was bonded to the equipment ground and ground rods. Each pedestal is treated like a separate structure.

I don't think 551.76(A) in the NEC allows this, and (C) forbids the neutral to be used for a grounding conductor. And there is no exceptions.

But I am surprised to see that the EGC is not required to be insulated as it is for manufactured housing.

(C) Neutral Conductor Not to Be Used as an Equipment Ground. The neutral conductor shall not be used as an equipment ground for recreational vehicles or equipment within the recreational vehicle park.

There is a very good reason for this. One is the fact that most sites will have a water supply and or other common metallic pathways. even earth could be dangerous if a heavy appliance was to startup and the voltage drop in the feeders was enough to cause a voltage potential between anything grounded to the neutral and Earth. Apply a short circuit load to these feeders and you would have a shock potential if a bare footed child happen to be holding on to the RV at the time the short circuit occurred. Remember a ground rod will have little effect on canceling this shock potential.

And if the above ever happens since you were the last to work on the system, you could be held liable.
Just something to think about.

 

[buck33k]

Re: rv park service and wire to pedestal??

Hurk27
"EGC required to be insulated as it is for manufactured housing." Could'nt locate this reference Wayne. Just for aluminum? Any help here would be appreciated.
Thanks, Buck

 

[iwire]

Re: rv park service and wire to pedestal??

Buck, In this case I believe 551.80 requires it.

 

[hurk27]

Re: rv park service and wire to pedestal??

If you are talking about a manufactured home then it's in 550.33(A)

I was just voicing my surprise that RV camps don't have to have an insulated EGC and now I know that only applies if it is copper thank's to Bob. But on a manufactured house it has to be insulated even if it is copper.
I just don't understand the discretion?

[ August 23, 2004, 07:42 PM: Message edited by: hurk27 ]

 

[buck33k]

Re: rv park service and wire to pedestal??

Hurk 27

Thankyou for the reference 550.33(A) requiring four insulated conductors, and thanks to Bob also.

Our local codes here in Wa. state(WAC rules) permit the bare copper EGC to a manufactured or mobile home. I don't know what the difference would be. Thanks again

Buck

 

[hurk27]

Re: rv park service and wire to pedestal??

Buck I don't know all the reasons for the insulated ground wire, but I do know this with the bare ground wire in contact with Earth if for what ever reason the service feeding this circuit has and elevated voltage on it grounding system as in a stray voltage. this EGC would slowly dissolve leaving the trailer without any grounding at all. This was a problem here on a trailer park that had a pad mounted transformer feeding about 25 trailers. The MV feeder to this transformer from the street had lost the MGN (Neutral/ground) at the pole. This caused the transformer to get its return through the Earth through anything in contact with Earth. While with the ground rods at the transformer and at each service did help and the fact that all the EGC's was bare no one knows how long it was like this. but eventually most of the EGCS dissolved and when a electric dryer element when to ground what ever was left just opened. This of course caused everything bonded to this EGC to go to 120 volts to Earth. Not a pretty picture. I'm not sure this was why the change in (I think "96" NEC) or not but it is one that I have seen for my self and makes sense.