Need to run a couple circuits underground at a church parking lot for some 400 watt mercury vapor parking lot lights. After the blacktop is trenched open I should be able to run the usual PVC underground and stub them up, either 18 or 24 inches deep (I'll check) without any problem with codes under a driving surface, right? Schedule 40 ok? I've seen too many wrapped ridgid installations still rust out over the years. Ridgid is not riquired under a driveway, is it?

we do 24" cover with sch 40 here, 18" radius 90s, usually 2" conduit is standard for us. 30" deep trench, 3" sand on the bottom, sand on top to about a foot from the top, then underground utility warning tape, then backfill the rest of the way with native soil, till the last 4" would be left open for AC patchpave. Some of this may be above and beyond NEC, just what we are doing on our job.

Ya may have to check with the city codes.

Mercury vapor? I doubt it. They don't make MV fixtures anymore. It's probably metal halide.

your probably right, but if the old ones are mercury vapor, are they interchangable?

Don't make Mercury Vapor fixtures? I thought the local box store had them ..... but then again, I haven't been there for a couple months.

For a parking lot, I want to stress two things:
1) The NEC is NOT a design manual. Just because the table might say 24", there's no reason to limit yourself to that figure; and,
2) You really don't want to ever have to dig the stuff up again.

So, here's what you ought to do:
1) First, make that ditch DEEP. 24" to the TOP of the pipe is a minimum;
2) Have LOTS of sand on hand. Put some in the bottom of the trench, lay the pipe, and cover with the rest;
3) While Sched 40 PVC is generally OK, I'd use wrapped rigid 90's and Sched 80 uprights;
4) I'd go up at least on, and preferably 2, pipe sizes;
5) The pipes would terminate at Christy boxes near each pole - not inside the pole;
6) I'd assemble the pipe using primer as well as glue - you don't want the pipe to come apart during compaction, paving, etc; and,
7) Compact the smithereens out of the dirt as you fill the ditch.

It seems to me that the major damage risk is from the paving operations, and not the traffic that follows.

OK, they do still make some cheesy fixtures to light up your backyard, but nothing that would light up a parking lot. And besides, who wants ghastly green light anyway?

Peter

No, they are not interchangeable. You need to match the bulb to the ballast.

I guess I misunderstood your original post. Are you adding brand new lights, or re feeding existing lights? If they are old they could very well be MV. If they are and the budget allows, I would replace them with new metal halide lights, or if they don't care about light quality and really want to light the place up, high pressure sodium.

Peter

I will be adding 5 more pole lights to the existing parking lot lights. Seems like schedule 80 would be better.

Schedule 80 is of little help: technique is all.

Use two step primer and solvent... like the irrigation boys: you don't want de-coupling during the compaction process.

In cold climates get below the freeze zone.

Oversize the PVC, with an absolute minimum of 1" for anything run out side a building.

A simple run does not justify a Christy box.

Watch out for collateral damage during the trenching process.

Sand is your buddy. I'd sand up the whole cavity ( subgrade )to save on compaction time. Such a belt of sand makes underground caution tape redundant. Just be sure to maintain dampness and compact relentlessly as you backfill in layers.

Get your conductors in BEFORE heavy paving equipment vibrates towards ultimate compaction.

Dip your makeup in Scotchkote or encapsulate them in 3M's epoxy packets... size D.

Be sure on your conductor sizing: CWA transformers take twice as much current to kick off as you might think. That means that 8 to 10 amps is a fully loaded Metal Halide circuit (with CWA ballasts) on a #10 THWN/THHN/MTW conductor tapping a 20Amp circuit breaker. #10 is the absolute minimum wire size for out door runs. #8 is EXTREMELY common. Local circumstances rule.

Good luck.

I have a bias in favor of christie boxes being place next to the poles for the following reasons:

1) There is seldom enough room in the light pole, or the pathetic little handhole in the pole, to work with the larger wires often used for these long runs;

2) Running wires directly to the poles greatly complicates replacement of a pole that has been damaged. With a box, at least, you can isolate the one pole easily, and remove the exposed wires;

3) Poles are getting crowded, with other cables ... speakers, cameras, convenience receptacles, etc.; and,

4) having the wires in the poles greatly complicates future replacement pulls of wire.

This still leaves room for some future re-paving job to cover up the boxes, but you can't idiot proof everything (they keep coming out with better idiots )

Reno I agree with your approach with one exception:
Usually they can't install these types of cables in poles without violating the NEC. The receptacles ok, but other cables probably violate sections in chapter 7 and 8 of the code that don't allow power and non-power cables in the same raceway and the light pole is now considered to be a raceway.

[This message has been edited by George Little (edited 02-10-2007).]

George, I wasn't saying it was right , just acknowledging reality.

I should also point out that I was not saying that code mandated my method in any way. I just wanted to show that "code minimum" might not be very wise in this instance.

Okay Reno. Hope your not offended because I always enjoy your input.

No offense at all George. I also appreciate your take on things .... even when I cheat!

Is the pole a raceway, though, or is it considered a listed fixture?

Steve- Look at 410.15(B).

Steve, there is some debate on that point. UL's answer depends, in part, on the length of the pole.

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( but other cables probably violate sections in chapter 7 and 8 of the code that don't allow power and non-power cables in the same raceway and the light pole is now considered to be a raceway.)
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You could run different cables in the same raceway if the insulation voltage rating on it was high enough, correct?

Cable jackets are separation. If you were snaking power in a pole with other circuits you could use something like MC in that segment of the pole.