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#97887 - 04/12/06 08:46 PM Greenhouse wiring  
Tripp  Offline
Joined: Sep 2005
Posts: 99
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.

2017 / 2014 NEC & Related Books and Study Guides

#97888 - 04/12/06 08:54 PM Re: Greenhouse wiring  
Tripp  Offline
Joined: Sep 2005
Posts: 99
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.

#97889 - 04/12/06 09:10 PM Re: Greenhouse wiring  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
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.

#97890 - 04/12/06 10:25 PM Re: Greenhouse wiring  
Tripp  Offline
Joined: Sep 2005
Posts: 99
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.

#97891 - 04/13/06 07:15 AM Re: Greenhouse wiring  
jfwayer  Offline
Joined: May 2005
Posts: 30
Fairmont, WV, USA
Use RNC, no 1/4" requirement, easy to bend, only problem would be expansion.


#97892 - 04/13/06 10:10 AM Re: Greenhouse wiring  
markp  Offline
Joined: Apr 2004
Posts: 60
Kent, WA, USA
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.

Kent, WA

#97893 - 04/13/06 11:28 AM Re: Greenhouse wiring  
PCBelarge  Offline
Joined: Jun 2003
Posts: 681
Dobbs Ferry, NY, USA
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.

Pierre Belarge

#97894 - 04/13/06 11:52 AM Re: Greenhouse wiring  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,140
I can't imagine the sun and heat effect would be any worse than the LFNC that runs to a sunbelt HVAC condenser.

Greg Fretwell

#97895 - 04/13/06 06:45 PM Re: Greenhouse wiring  
Tripp  Offline
Joined: Sep 2005
Posts: 99
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!!!

#97896 - 04/13/06 08:06 PM Re: Greenhouse wiring  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,140
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.

Greg Fretwell

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