is it legal to have RMC runs exposed outdoors?

[rselina]

Hey Guys,
My facility is having a dispute with the local building authority and I am hoping one of you may be able to clarify the issue, since I have been unable to find anything in the NEC to explicitly ALLOW or PROHIBIT our plan, but I'm a rookie at all this . Anyway, the story goes like this:

The facility in question is an remote observatory at 10,000ft. There is a spring approximately 8000 feet away. We will need a pump down at the spring and the dispute is how the wire has to be run to the pump. The voltage will be under 600V and it will pass through uninhabited forest (no dwelings). We wanted to run steel galvanized sch 80 pipe as a RMC in direct contact with the earth, ON GRADE. The pipe will be anchored at appropriate intervals. It is cost prohibitive to bury the conduit or encase it in concrete due to the rocky nature of the area. The building authority is suggesting that PVC conduit buried 18" is the only way to meet code. I figure worst case according to Article 300, we bury it 6" in RMC, but we'd really rather not have to do this given the terrain. If you could clarify the issue I would be most grateful.
Thank you,
Rob Selina
Magdalena Ridge Observatory
801 Leroy Pl.
Socorro NM 87801
Voice: 505-835-6649
Fax: 505-835-6807

[ June 06, 2003, 05:18 PM: Message edited by: rselina ]

 

[roger]

Re: is it legal to have RMC runs exposed outdoors?

Whoa, 8000'! What size is the pump? Has anybody figured the voltage drop for this run? It seems the size wire and conduit needed and the associated price is going to be an attention getter in it's self.

Is there utility power at the site or are you generating your own?

If you must run to this pump, it would be better to set poles and run this as an overhead open wiring system.

Roger

 

[rselina]

Re: is it legal to have RMC runs exposed outdoors?

Originally posted by roger:
Whoa, 8000'! What size is the pump? Has anybody figured the voltage drop for this run? It seems the size wire and conduit needed and the associated price is going to be an attention getter in it's self.

Is there utility power at the site or are you generating your own?

If you must run to this pump, it would be better to set poles and run this as an overhead open wiring system.

Roger

Roger,
I should clarify, first the run is 8000 feet but the vertical drop is 2000 ft. The pump is pretty small, it will pump about 3 gal/min at 900 psi (about what the vertical run turns out to be). It will need a 2HP electric motor, that's all we have to run down there. We have a pole line coming up to the site that is in the process of being upgraded (another one of my projects) It's a 7200V system and we're going to 21kV 3 phase. I'm thinking that a small generator at the pump or better yet solar cells are the way to go, but I need to do more research. The project manager prefers to run it off of the main site's power supply so I'm looking into this first. Poles will not be an option, we have to comply with the forest service on this one and they do NOT want another pole line up the mountain. It's either on the ground, burried or not at all. Thanks,
Rob

 

[roger]

Re: is it legal to have RMC runs exposed outdoors?

Rob, bear with me here. The verticle drop has nothing to do with the electric part of the installation, but probably does in the water delivery part.

In otherwords, 8000' is 8000' as far as wires and electricity.

Take the formula for finding wire size:

CM= 2 x approximate K x D x I
______________________________
VD allowed 3% of 240=7.2

(3% is just a value I picked)


CM= circular mills

K = resistance of a circular mill ft (12.9 for this example)

D = distance one way
I = amps = (12 for a 2 hp 240v 1 phase motor)

2 x 12.9 x 8000 x 12 = 2476800 / 7.2 = 344000

Or 350 MCM

This would literaly be tons of weight to pull through your conduit and splices at pull points.

Please forgive me if it sounds as though I'm talking down to you. And then again, maybe I'm just not understanding what you are actually doing.

Roger

[ June 06, 2003, 07:58 PM: Message edited by: roger ]

 

[electricmanscott]

Re: is it legal to have RMC runs exposed outdoors?

All that aside, you can't just lay the pipe on the ground. Someones got some serious digging to do.

 

[tom baker]

Re: is it legal to have RMC runs exposed outdoors?

RMC can be run exposed on grade, but if buried it must be per the burial depth in 300.5.
However you are far beyond the normal distance for voltage drop and need to look at other options.
this must be piston or positive displacement pump to overcome the head pressure, esp if its only 2 hp.

Is it a flowing spring? you might consider a ram pump. It requires no electricty and only the effect of free flowing water.

Otherwise, you'll need power at the site. There are a number of solar sytems that can and have been used for pumping water, do a search for Real Goods, they have a lot of information on solar systems.

 

[gwz2]

Re: is it legal to have RMC runs exposed outdoors?

If the 7200 ( or other power is near the pump why not feed it from another service on the 7200 and radio control the pump site ?

How is the water to be piped with-out ecco problems?

Run the water and and the electrical in the same trench, but the Vd would be a major problem, conductor size-wise.

 

[bob]

Re: is it legal to have RMC runs exposed outdoors?

I agree with gwz2. If you primary line is near the pump, bury a 15 kv cable and install a small pad mount transformer to provide the service. It is a lot cheaper that 8000 ft of 350 copper 600 v cable. Even if you could lay the conduit on the ground you would need 20 or so pull/splice boxes to get the cable to the pump.
The primary voltage is the cheapest and simplest way to go.
An other option is to hang a pole mounted transformer on a pole close to the pump and install an overhead service if that permissable.

[ June 06, 2003, 11:49 PM: Message edited by: bob ]

 

[electricmanscott]

Re: is it legal to have RMC runs exposed outdoors?

Tom, you have my attention. Where is the allowance for running RMC on the ground. Can't seem to find anything in the book.

 

[bennie]

Re: is it legal to have RMC runs exposed outdoors?

There appears to be a mile and six tenths of pipeline. What is the change in elevation?

There is more problems than power. Has this project been engineered?

This looks like a water tanker operation.

 

[gwz2]

Re: is it legal to have RMC runs exposed outdoors?

Not that I like to see RMC surface mounted on earth, paving, etc., I do not see anything prohibiting such installation if done per 300.7, 300.10, 300.11, 300.12, 300.18 344.10 and 344.30.

Just adding; many temporary installations do not meet 527.2(A) such as in the first paragraph.

[ June 07, 2003, 12:54 PM: Message edited by: gwz2 ]

 

[pierre]

Re: is it legal to have RMC runs exposed outdoors?

Hello rselina,
How often is the pump to be run, 1 hour a day , 6 hours a day, etc...?
If the pump is not run too often, I see a generator as your answer. By the time you trench, pipe,pull wire and all the other good stuff, you could install one heck of a generator with an on site tank for fuel, of course depending on the environmental issues.

Pierre

 

[pierre]

Re: is it legal to have RMC runs exposed outdoors?

electricmanscott,

300.5 table, tells you the required depth of burial for raceways, cables, and conductors.

Pierre

 

[tom baker]

Re: is it legal to have RMC runs exposed outdoors?

If the conduit is not buried it is exposed. And it can lay on the ground, supported on piers-this is no different than running conduit on a roof to a HVAC unit. One of my coworkers ran (under direction) a 3/4 RMC conduit behind a guard rail to a street light. He didn't like it, I didn't like it, but its not a code violation...

 

[iwire]

Re: is it legal to have RMC runs exposed outdoors?

If we go with Rogers estimate of 350kcmil we can figure it will be at least 3" RMC so he could move the supports out to 20' as per Table 344.30(B)(2) Supports for Rigid Metal Conduit.

I would think a bag of quickcreate every 20' with a small piece of strut sticking up vertically to clip the RMC would secure it enough. I would keep the RMC as low to the ground as possible but up off the ground for the same reason we keep airspace behind equipment mounted in wet locations.

3" or 4" RMC with 350kcmil is not going to move much any way.

And honestly what is someone going to have with them that far out of the way to do harm to 3" or 4" RMC?

You did not say the voltage but if possible go for 480 volt 3 phase, this will help with voltage drop.

[ June 07, 2003, 05:31 PM: Message edited by: iwire ]

 

[iwire]

Re: is it legal to have RMC runs exposed outdoors?

I did some checking and if you can get the 2 HP pump in 460 volt 3 phase the current would be 3.4 amps.

This would allow 3 - 3 AWG copper conductors to run out to the pump and stay at no more than 3% voltage drop when running, but if this is a positive displacement pump you may need larger conductors for startup currents.

This would easily go in 1/1/2" RMC with supports needed every 14'

 

[bennie]

Re: is it legal to have RMC runs exposed outdoors?

8000 feet of metal pipe will have a lot of expansion, and contraction, throughout the day, depending on high and low temperatures.

Pardon me, but this is a foolish plan. Get an electrical and hydraulic engineer to review this installation.

If the change in elevation is too great, you will need lift stations.

Consider a storage tank and hauling water to the site.

 

[iwire]

Re: is it legal to have RMC runs exposed outdoors?

Originally posted by rselina:
the vertical drop is 2000 ft. The pump is pretty small, it will pump about 3 gal/min at 900 psi (about what the vertical run turns out to be). It will need a 2HP electric motor,

It looks like he has the rise covered with a 900 PSI pump, and expansion and contraction can be overcome.

 

[bennie]

Re: is it legal to have RMC runs exposed outdoors?

The only way you can get a column of water to 2000 feet is haul it in a tanker truck.

 

[tom baker]

Re: is it legal to have RMC runs exposed outdoors?

What kind of pipe will you use that will withstand 900 PSI?