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RV...Motor home Park advice ??? #186180 04/24/09 06:56 PM
Joined: Jun 2007
Posts: 19
site351 Offline OP
I was asked to give a price on a RV-Motor home park and have some rough drawings (no electrical secondary) and it just shows the parking spaces, Primary feed lines for the Power company and 6 pad mounted transformers throughout the circular drive. They require 3" long sweep PVC 90s to be stubbed out of the fiberglass vaults that the pad mounted transformers sit on. There are 38 parking spaces and 38 three inch pvc 90s shown ...maybe 6 at this transformer... 5 at the next one ... and so forth.

I've never wired one of these parks's easy....but I'm looking for the least expensive way and
easiest...quickest method.

Option #1...
Reduce down the 3" 90s to maybe 1 1/4" pvc and go straight to the metered pedestals. Not sure if I need a
Main Breaker. Pedestals will contain 3 breakers, a 50 amp 4-wire receptacle, 30 amp 120 volt outlet, and one 120 volt GFI outlet. (Haven't priced the pedestals yet)

Option #2
Use a 5 or 6 gang meter pack next to the transformer and maybe a 80 amp main breaker to feed each non metered pedestal. Just requires one 2 1/2" secondary conduit from each transformer to each meter pack...and a lot easier for the meter reader...may be able to eliminate a couple of transformers??

Option #3
Loop one 2" pvc and feeder wire from metered pedestal to pedestal. Need to do a load calculation and see how many could be tied together...this also could reduce the number of transformers.

The RV parking spaces are about 20 feet wide and 50 feet long and on 4.5 acres. The plans do not show the KW rating of each transformer....but I think that six for 38 RV parking spaces is overkill since most heat requirements are
propane and most RV homes are 120 volt/30 amp....

any advice ??

Business, Office, Estimating, Legal:
Re: RV...Motor home Park advice ??? [Re: site351] #186185 04/24/09 11:32 PM
Joined: Jul 2004
Posts: 9,571
gfretwell Online Content
I inspected some state park trailer hookups and they were changing the 120v 30a to 250v 50a because that was what most new RV users wanted. These guys usually have a ton or more of A/C these days and people want to use it.

Greg Fretwell
Re: RV...Motor home Park advice ??? [Re: gfretwell] #186190 04/25/09 06:39 PM
Joined: Mar 2003
Posts: 849
Yoopersup Offline
I've done several Parks like this. Theresa lot more to them then you think. Voltage drop is a Big factor for one thing.
Lotta the Manfactors that supply Equipment for theses have software programs that well do all the calculations for you. JUST make sure you read 551 completely.
The last one I did they wanted 80% of sites rated for 50 amp plugs due to the larger RV's nowadays.

Re: RV...Motor home Park advice ??? [Re: Yoopersup] #186192 04/25/09 09:23 PM
Joined: Jul 2004
Posts: 9,571
gfretwell Online Content
If possible, try to get the utility to run as much of the distribution as you can get with medium voltage. Drop transformers and feed the sites from the center. It always amazes me how much load diversity they assume. I believe the last one I did had a 25KVA (may have been 37) for six 50a sites. If they are back to back sites, the service conductors are pretty short.

Greg Fretwell
Re: RV...Motor home Park advice ??? [Re: gfretwell] #186197 04/26/09 01:45 PM
Joined: Jun 2007
Posts: 19
site351 Offline OP
I suppose my basic question is what the normal mode of wiring these things is. It seems the way this thing is drawn is like a subdivision with homes having 200 amp loadcenters.
Yet we're feeding each space with just a maximum of 50 amp
outlet ? If the fifty amp is used and we feed each space with individual runs...then thats just 5 or 6 two pole outlets coming off one transformer ?? If the 50 is used in each space...its unlikely the 30 amp will be used. Now I agree voltage drop could be an issue on 4.5 acres. The spaces for the most part are side by side...and I suppose its possible to loop a 4/0 or pratt 250 alu. wire and catch 7 or 8 metered spaces and stay fairly close to the transformers.

The power company is charging the owners a little over
25,000 bucks to install one lift pole and pull the primary wire in. The owners are responsible to install the six fiberglass vaults and run the 2" pcv conduit from vault to vault. Of course the power company sits the transformers.

I probably need to drive around and look for a fairly new park and see what others have done.

I have a few days to come up with a price and I appreciate the replies....any additional comments always

Re: RV...Motor home Park advice ??? [Re: site351] #186198 04/26/09 08:24 PM
Joined: Jul 2004
Posts: 9,571
gfretwell Online Content
I would try to get the vaults in the center of the loads they serve (not on one end). That helps your voltage drop/copper problem. I have seen the drops run in a string (big copper, stepping down) or radially with smaller copper depending on the layout.
I have seen a main and 6 breakers or exploiting the "outside tap" rule with just a main Polaris blocks and the breakers on the pedestals (watch the engineering on this one).

Greg Fretwell
Re: RV...Motor home Park advice ??? [Re: gfretwell] #186229 04/27/09 10:08 PM
Joined: Jun 2004
Posts: 1,273
Tesla Offline
Depending upon the size of the park, hence the length of the runs:

If the utility meters power to you at 4160V 3 phase...

Route most everything at this voltage. Use fuses as against circuit breakers. Step it down at the last moment with dry type transformers with rain shields. (makes them 3R)

Mount a NEMA3R disco directly to the transformer (37kVA ?)

Multi-tap it to six or fewer load pedestals using the tap rules... And since it's buried and out doors... The tap rules are very forgiving...

Provide 50Amp OCPD at the load side at the pedestals.

Ground and bond the Wye Secondaries at the transformers and provide an additional ground rod/ufer at the pedestals.

Situate the transformers so that they are not eyesores and so that they can't be rammed by the clients.

The Code permits medium voltages to run even shallower than low voltages, so you might save on trench depth.

Aluminum medium voltage conductors will cost less.

When you check out existing work focus on recent stuff and take a note as to which contractor won the bid.

Low voltage distribution normally uses too much pipe and wire. It's the distances that do it in. Any reasonably sized RV park is many hundreds of yards on a side.

BTW, more and smaller transformers will permit the operator to simply shut some down. Idle transformers bleed energy, of course.

The NEMA3R disco at the transformer might even be eliminated if you can engineer it right. You'd use the OCPD at the pedestals to handle transformer faults. Up the line the fuse would provide protection.

4160Y120 dry type transformers are an off-the-shelf item and are no more difficult to hook up than 480Y120 units.

Every transformer manufacturer I've ever known will crank them out in short order. The NEMA3R shields are an add-on, be sure to order them.

You might even get the manufacturer to paint them green for you...

Re: RV...Motor home Park advice ??? [Re: Tesla] #186254 04/28/09 04:01 PM
Joined: Mar 2003
Posts: 849
Yoopersup Offline
I always thought RV parks must be 120/240 volt single phase. But 551.40 seems to say 120/208 3 phase is allowed.
Am I reading that right???

Re: RV...Motor home Park advice ??? [Re: Yoopersup] #186258 04/28/09 10:24 PM
Joined: Jun 2007
Posts: 19
site351 Offline OP
I have a 2005 code book and what I read is any line to line
equipment shall be rated 208/230 volt.
I suppose 3 phase could be used in a park and you could feed
loadcenters 3 phase 120/208. Not practical...but you could.
However, there is nothing, that I'm aware of, in the Motorhomes that uses line to line voltage. 3 phase..line to neutral is 120 volts.
This is the first time I've been involved with an R.V. park and was told even the Big homes that everything is 120 volts. The bigger 50 amp R.V. plug is just like a range outlet basically except both phase (hot) wires share the neutral...nothing line to line inside the home.
There may be some instances where equipment is used 208/230,
I bet not very often.

Re: RV...Motor home Park advice ??? [Re: site351] #186259 04/28/09 10:37 PM
Joined: Feb 2003
Posts: 939
frenchelectrican Offline
. If you want more details just look up NEC art 555.72 {2005 editon }

it do allow triphase supply to used in larger RV parks and some POCO may limited the single phase supply to their transfomer size.

I know one RV park near me in Wisconsin do have triphase supply { the newer section of the park do have it the old section still on 1 supply but the transfomer is pretty big for our POCO 125 KW single can. you can imaged the size of secondary conductors blink


Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

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