Anybody out there have experience wiring a greenhouse? I've been asked to wire one that is in the shape of a geo-desic dome, and I'm trying to figure out what to use for raceway. Because of the dome-shape, flexibility would be a real help so I'm thinking of using seal-tight (LiquidtightFlexibleNonmetallic Conduit). I can't see any code problems as long as I secure it at the proper distances.

Any other ideas from anyone? Thanks.

I just looked at NEC 300.6(c) and am thinking of its application in a greenhouse. Specifically, how would I keep the conduit 1/4" off the beam?

This is an entirely new area for me, so I'll be ecstatic to hear anyone else's experience.

I have not done any dome work- this sounds like an interesting challenge!

A geodesic dome is actually an assembly of pentagons and hexagons, with triangles filling each "major" shape. Rather than a smooth curve, there is a slight angle at each junction.
Unlike a conventional building, the shape itself is what gives it its' strength, rather than specific structural members. The effect of this is that the only place you can safely place an anchor is dead center where the major shapes come together.

With that in mind, it seems that you'ld either have to run romex, zig-zagging along the frames....or build some sort of trellis to support your stuff. An arched "ladder" made from strut comes to mind. Or, you could be conventional, and "build a box" within the dome, so you can run your pipe in the usual manner.

Reno - I was thinking no romex because of the moisture factor. Also, not sure what you mean by "build a box". Do you mean create a structure within the structure? Don't think that would work: the triangles of this dome are translucent pieces made specifically for that filtered sunlight effect; don't want to block them in any way. The structure connecting each triangle to the next is 2x4 wood, with the 2" face being the surface I could strap to. Not too concerned about that. Just wondering if sealtight seems like a reasonable way to go and, if so, how to go about strapping with the 1/4" spacing required by 300.6(c). Thanks.

Use RNC, no 1/4" requirement, easy to bend, only problem would be expansion.

LFNC-B is a non-metallic conduit, so why do you need to keep it 1/4" off the beam? I always thought "sealtite" was LFMC, and since that has metal would have to be off the surface. LFNC is cheaper, non metallic, and easier to work with.

Will you have any issues protecting the conduit from physical damage? You could also use UF cable. It should have the same physical damage constraints and plastic conduit and may be easier to protect because its much flatter.

Is the dome metallic open framing or wood open framing.

I can see the use of LFNC as a good way of following the shape of the dome. My only concern is the heat from the sun and the dome.

I can't imagine the sun and heat effect would be any worse than the LFNC that runs to a sunbelt HVAC condenser.

Good question, Markp, about the 1/4" airspace for LFNC. I quess when I read 300.6(c), it's not clear to me that they are referring to just metallic materials: "...the entire wiring system, where installed exposed, including...all conduits and cable, shall be mounted so that there is at least 1/4" airspace...." That sounds to like even UF cable would require the airspace. You think maybe I'm misinterpreting?

As for the possibility of using UF, I would love to go that simple route, but I'm afraid "subject to damage" might be an issue in this greenhouse. It's a very dynamic space, with an upper deck and waterfalls, etc., plus constant digging and planting. Not your ordinary retail greenhouse, but more of a personal botanical garden.

RNC is probably the best way to go, though "easy to bend" doesn't exactly fit my experience. I haven't yet wanted to shell out the bigbucks for a heating blanket and so have made do thus far with a heat gun: SLOW!!!

Half inch RNC is pretty bendy stuff. As long as the dome has a reasonable raduis you should be fine. I userd 3/4" RNC for the bows in my boat lift cover. That has a pretty good bend in it too.
I think the 300.6 exception should ease your concerns about the 1/4"

Exception: Nonmetallic raceways, boxes, and fittings shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface.

Glass is similar to tile IMHO.

Hey Greg- I just checked the UL White Book and it says RNMC is not Listed for boat lift covers and you'll need "Special Permission" signed by at least 5 inspectors and you and I know that those 5 inspectors will need some "encouragement" and a boat ride before they sign off on "special permission"

I have already taken 3 inspectors for that boat ride and provided some 12 oz ecouragement but if you think we need one more come on down.

Greg - 300.6 exception doesn't mention wood. The 2x4s between triangles is what I would be strapping to. Back to you.(pin-pong anyone?)

It is clear the wood is what you should be worried about. If it is treated it shouldn't rot. The RNC will be fine.

You really need to back up and read the scope of 300.6 before we start nitpicking the language. Lets start over.

It doesn't even sound like we care what 300.6 says if we use a plastic wiring method

I have used the Carlon clamps for years and they do a good job of raising the RNC just a little off the surface and at the same time allow it to slide with expansion and contraction better than an ordinary 2 hole strap. Would be my choice here. http://www.carlon.com/Brochures/2B10-Straps_Clamps.pdf

I have wired over 5 acres of production greenhouse. In Ohio where I did it, it was agricultural and not subject to inspection.
The inspector didn't even want to discuss methods.
I have seen RNC used and it turns into a terrible mess in a few years. The temperature swings make it expand and contract until it pops out of straps and busts fittings. If the greenhouse is unused and the heating and ventilating systems are shut down an 80 degree swing is easily possible.
Also the condensaion that occurs will fill any watertight raceway until the devices are swimming.
The best job I feel is done with EMT and set screw fitting to let the moisture out.
I have run EMT following the curved portions of the structures pretty sucessfully. Try using small bends at intervals and minis as straps.
Any tie wraps or T-stat/Low voltage wiring needs to be UV resistant or it will be toast in a couple years.
If it is a commercial operation the oxidation from the pesticides and fertilizers also will hasten the degradation.

Good Luck

Wet location, aluminum MC?

added;
Drip loop so you enter the bottom of all boxes

[This message has been edited by gfretwell (edited 04-15-2006).]

More great ideas and input. Thanks to everyone. Keep those cards nd letters coming!