Greenhouse wiring

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dema

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For branch circuit wiring in a greenhouse at a school, what kind of conduit or cable would you use to run exposed. My thought was Schedule 80 PVC supported at 5' intervals. This is 3/4" conduit. Just lighting and receptacle circuits and a couple of small heater/ventilators. The contractor was going to use PVC coated MC cable but the owner was concerned about snaking. They asked me about it and I said I would have used the Schedule 80 PVC supported on 5' centers. But now they want a statement saying that it won't snake. Well, nothing short of PVC coated RGS is going to stay straight for sure - and they don't want to pay for that. But what do you experienced people think would be best, given that this job is supposed to be cheap, cheap, cheap.
 
dema said:
For branch circuit wiring in a greenhouse at a school, what kind of conduit or cable would you use to run exposed. But now they want a statement saying that it won't snake. But what do you experienced people think would be best, given that this job is supposed to be cheap, cheap, cheap.
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Put a few more straps on it and it won't snake (at least until the warranty is up).

What I really think is that it's a greenhouse and schedule 80 should be fine.
 
depends on if it's getting wet. i have run in EMT with regular 4 squares in the ceiling area four runs the entire length of a commercial greenhouse, with permit, and passed no worries. if it's getting sprayed with water they still make rain tight emt fittings and boxes. if you still want pvc, then throw in a few extra expansion fittings, as stated above,
 
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mwm1752 said:
What location is a greenhouse classified as? Dry/damp/wet and where would you find it in code
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I have the same question. Most greenhouses only have regular water exposure on the floor and maybe lower portions of walls, unless they intend to regularly hose the entire place down. I would think luminaires would usually be in dry or damp locations, receptacles and switches could be dry, damp or wet, and need to be determined on an individual basis.

Next comes corrosiveness of the environment. Fertilizer use in such areas is usually minimal and not all that corrosive. If you want to see a real corrosive environment because of fertilizer products, come to buildings used for larger agricultural operations that the primary function of the building is to house and handle fertilizer products. The green house in question may only have a small area that has such concentrations at the worst.
 
My family has owned greenhouses my whole life.

Glass covered greenhouses are often quite damp due to condensation (especially night and early mornings during cool/cold weather when they are closed tight). It is common for the condensation to mainly run down the glass and glazing bars (if metal), but there might be some dripping. These greenhouses also have the biggest temperature swings due to the high light transmission. There is always a little ventilation due to glass lap joints unless they are sealed or frosted.

Polyethylene film covered greenhouses can also experience substantial condensation, and it is more likely to drip than run near the top of the greenhouse. Double film inflated greenhouses are most common. Light transmission is a lot less than glass, but so is ventilation unless vents are open or fans are exhausting.

Corrugated polycarbonate will have the least condensation (best R value) and light transmission between glass and polyethylene film.

In my area inspectors are always confused about what regulations apply in a greenhouse because agricultural building rules apply. I just treat the whole growing area as wet. PVC conduit may snake a little, but I usually secure it every four feet. Our glass greenhouses have 24" wide panes, so that means a strap every second glazing bar.
 
I forgot to add that while polyethylene film greenhouses are normally stripped and re-covered every few years, glass can last for decades and must be cleaned periodically. We last reglazed 1/2 acre of glass greenhouses in the late '70s, although we have replaced individual panes since then. We clean the inside of the glass every few years with a solution using di-hydrogen fluoride, so the solution is basically weak hydrofluoric acid) then rinse it with plenty of water. Wet and corrosive.

Also, greenhouse humidity can be very high due to plant transpiration even if little free water is spilled, e.g. if watering with drip irrigation. Humidity will depend in this case on crop type, growth stage, CO2 levels, sunlight, etc.
 
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I can only say that I have seen a few that have been wired in EMT. Not sure of the age when I saw them but the EMT was in disastrous condition. Heavy rust/corrosion.
 
dfmischler said:
My family has owned greenhouses my whole life.

Glass covered greenhouses are often quite damp due to condensation (especially night and early mornings during cool/cold weather when they are closed tight). It is common for the condensation to mainly run down the glass and glazing bars (if metal), but there might be some dripping. These greenhouses also have the biggest temperature swings due to the high light transmission. There is always a little ventilation due to glass lap joints unless they are sealed or frosted.

Polyethylene film covered greenhouses can also experience substantial condensation, and it is more likely to drip than run near the top of the greenhouse. Double film inflated greenhouses are most common. Light transmission is a lot less than glass, but so is ventilation unless vents are open or fans are exhausting.

Corrugated polycarbonate will have the least condensation (best R value) and light transmission between glass and polyethylene film.

In my area inspectors are always confused about what regulations apply in a greenhouse because agricultural building rules apply. I just treat the whole growing area as wet. PVC conduit may snake a little, but I usually secure it every four feet. Our glass greenhouses have 24" wide panes, so that means a strap every second glazing bar.
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1/2" thru 1" PVC is supposed to be secured every three feet according to T352.30, so unless it is larger conduit sounds like a support is needed at every glazing bar to me.
 
Can anybody point me to the code reference, or product listing, for 3/4" schedule 80 PVC with supports 5' on center? I couldn't find anything. It is suggested in the first post in this thread that it is allowed.
 
dfmischler said:
Can anybody point me to the code reference, or product listing, for 3/4" schedule 80 PVC with supports 5' on center? I couldn't find anything. It is suggested in the first post in this thread that it is allowed.
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As I mentioned in post 13, Table 352.30 - applies to all rigid PVC raceways. Sizes 1/2 inch thru 1 inch must be supported every 3 feet, this is for both schedule 40 and 80.
 
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