Feeling Overwhelmed... small RV "park" buildout

[jerm]

[FONT=arial, sans-serif]It's been awhile, but here I am, with an issue that I know someone on the forums can at least give me a clue on. I've read the entire article on conductor sizing at [/FONT]http://www.mikeholt.com/nec-conductor-sizing-and-protection.php but I'm not entirely sure where to start on a small enginnering project.

For those who don't remember (and why would you!?), my background is commercial and industrial projects (I'm a journeyman in OK) that typically come with a set of prints. I'm also great at transformers, motor controls, automation, running long overhead lines to oil wells...

For the "where do I even start" project, I'm involved with a local club that has a big event once a year that typically brings out the RV's, and with them, the generators. Over the past three years, I've been slowly bringing the club's electrical infrastructure up to code (what a mess) and I'm to the point of wanting to add "some" (8?) pedestal rv outlets, TT-30's probably, (maybe 14-50's instead) and I'm just not sure how to most efficiently size the wire and overcurrent devices. I guess I'm not really clear on if I'm really running feeders or branch circuits, as weird as that may sound... let me explain...

Midwest makes an unmetered nema-3 enclosure that has a TT-30R and a 30-amp breaker inside. Does that make it a "panelboard?" It occurs to me that I can probably dig up the definition in article 100... If it is a panelboard, is the branch circuit just the recept with a 6 inch wire to the breaker? Can I just run 3/0 off a 200a disconnect and loop between all of them in a row? Half-way down the row, the total amperage on the line would be much less, but I can't really drop down to something like #4 because I've got to protect the wire and a 200a disconnect is not going to protect a #4...

What about continuous and non continuous amperage on this kind of situation? 355 days a year there's 0 amps on these. when an RV plugs in, their plug goes to a panel inside the unit.

It seems there are 1000 code questions that come to mind that I just don't know the answers to. And I'm generally very good with code questions and answers!

I know that one answer is "AHJ" -- but assume I'm on an indian reservation where things are done to code only because I want them to be...

Thanks for any guidance?

 

[augie47]

Your basic plan is good, but you need to start with Art 551.
It will show you what receptacles are required and how many.. keep in mind that's a minimum requirement and it will guide you in sizing the feeder to all 8 if you wish to follow that route.
Depending on the arrangement, you may feed each location with branch circuits from a central panelboard or you may find that looping a feeder is more practical and economical. (The looped feeder is most common in this area but with just (8) you may find individual circuit the best)

 

[jcbabb]

I've done several RV parks for the state. I generally provide a bank of disconnects on a rack next to the utility transformer. Each disconnect feeds a 'circuit' of 3 to 5 RV pedestals.

Your wire size is driven by the size of the main disco, but you need to factor in voltage drop as well (assuming the pedestals will be spread out over considerable distance). I usually throw together an excel sheet to calculate the segmented voltage drop for each section just to be sure.

Article 551 is pretty clear on load calcs, so check that out first.

 

[Cow]

Over here they consider them feeders and each pedestal required a grounding electrode. Keep the feeders in mind when you factor your permit fees. The boss couldn't believe it when he bid an rv park and found out the fees were going to be in the neighborhood of 6k.

 

[mopowr steve]

Having done a couple RV parks myself I would like to inform you to go over the minimum requirements set by the NEC. We have a campground in a fairgrounds that was done by an engineering firm which used the minimum requirements at the time but what was not considered was that many campers also brought in extra refrigerators for beer/etc so now we will trip disconnect breakers on very hot days when A/C s are running full tilt.
So as a thought I know it's only a couple days to a week of use but that campground will push the limits if not up sized especially with newer/larger campers with multiple A/C s.
Your thought of use of only couple days is also what our power company used in their thought of sizing secondary and transformers well guess what ...... 2 of their overhead lines fried in half and they also had to upsize a transformer from their original thought.
The last campground I done we figured all sites with 50 amp, used 2 different sizes of underground 350 MCM Alum.(which was the largest wire the lugs would accept in the pedestals) and then to 2/0 Alum. further in the run I think we had 8 or 9 sites per disconnect. But you'll have to do the calcs for your particular situation.

 

[mopowr steve]

Over here they consider them feeders and each pedestal required a grounding electrode. Keep the feeders in mind when you factor your permit fees. The boss couldn't believe it when he bid an rv park and found out the fees were going to be in the neighborhood of 6k.

Question, the pedestal you used did it have a 3 hole lug for EGC in and out then one for grounding electrode? Just wondering why they required a ground rod at each pedestal.
Because the Midwest and Milbank ones I've used only had 2 hole lugs for EGC in and out.
Like you said these are fed by feeders.

 

[Cow]

Question, the pedestal you used did it have a 3 hole lug for EGC in and out then one for grounding electrode? Just wondering why they required a ground rod at each pedestal.
Because the Midwest and Milbank ones I've used only had 2 hole lugs for EGC in and out.
Like you said these are fed by feeders.

I only saw the pedestals stacked in the shop, but I wasn't on this job, so I couldn't tell you how the ground lugs worked out.

As far as the ground rod, I assume the inspector was considering each pedestal a "structure" and applying 250.32(A).

 

[augie47]

I only saw the pedestals stacked in the shop, but I wasn't on this job, so I couldn't tell you how the ground lugs worked out.

As far as the ground rod, I assume the inspector was considering each pedestal a "structure" and applying 250.32(A).

I have seen many installs where a grounding electrode was not required by the AHJ. I believe the '14 Code clarified that 250.32 does apply, but note that 250.32 addresses single branch circuits differently than it does feeders.

 

[Smart $]

Also, don't forget outside feeder taps are not length limited.

 

[jcbabb]

The ground rod was required at each pedestal on every job I've done.

Here is the model for the pedestal: Midwest MODEL U075CP6010

 

[mopowr steve]

The ground rod was required at each pedestal on every job I've done.

Here is the model for the pedestal: Midwest MODEL U075CP6010

Looks like the one we've used, but still how did you attach the ground rod when the lug supplied only had two holes 1in and 1out for the equipment ground or were yours used as service equipment straight from a transformer where the supplied bonding wire attached to the lug and the other hole for rod.?