Running power to backyard greenhouse

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  #1  
Old 12-03-12, 08:37 AM
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Running power to backyard greenhouse

I just installed a 120 sqft greenhouse in my backyard and now would like to get power out there for lighting and ventilation. I do not need a heater, and so I am settling on supplying 30A 120V (I'll be running a few low voltage water pumps out there as well).
Facts:
200A to main panel, with 6 positions available
90ft total run from main panel to greenhouse (15ft routed through garage walls, 75ft underground)
I'll need to run 3 90 degree turns with the interior conduit- 2 in the garage and 1 from the ground up to the greenhouse (but the underground portion is a straight shot)
I have an open 18" trench already dug between the garage and the greenhouse.

Current Plans:
- 1 1/4" PVC conduit for electrical, buried 18" underground
- subpanel installed in greenhouse
- 3/4" PVC conduit placed in trench @ 12" for future comms lines (since the hole is already open)

Questions
What type of wire is recommended for the job?
Is the plan to bury the conduit buried at 18" compliant with national code?
Does code require irrigation lines to be run a certain distance away from the electrical conduit? I know for a fact that there is a water line from my well to the house that intersects the electrical run, but the water line is 36" down (i.e., 18" below the proposed location of the electrical conduit)

I realize that I'll probably have to provide additional information to get more specific recommendations, so I am happy to do so.

I am planning on reading Wiring Simplified, as recommended by Furd in previous posts concerning similar applications.

Thanks in advance for any help or guidance.
 
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  #2  
Old 12-03-12, 09:02 AM
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I'll let a Pro answer on the wire....but just a hint. After you get everything installed, cover the conduit with about 1/2 the dirt and then lay in a piece of yellow caution tape the full length before finishing the backfill. Might even be able to find some with "buried cable" printed on it.
 
  #3  
Old 12-03-12, 09:31 AM
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With conduit you will need to run #10 THHN/THWN wire for each wire. (hot/neutral/ground) I suggest stranded wire for ease of pulling. You will likely need to add a J-box where the run penetrates to the outside. You may only have 360 degrees worth of bends in a conduit run between pull points. It is best to keep it less than that. IMO 1" pipe would be plenty large unless you planning for the future.

You will need some type of sub panel in the greenhouse so that you can reduce the 30 amp feeder to 20 or 15 amp branch circuits. Another option is to run a 20 amp multiwire circuit (Hot,hot,neutral,ground) You would only need #12 THHN/THWN but you would gain 25% more capacity and have 240v if needed. You would also not need a sub panel (unless you want one) but you would need a disconnect which could be as simple as a two pole switch.

Water lines and electrical lines can be run next to each other without issue.
 
  #4  
Old 12-03-12, 09:00 PM
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To expand a little on Tolyn's comment, I would either:

Run 30A at 240v (10ga H/H/N/G) to a subpanel. This will give you enough power for the future and allow you to use 240v heaters which may be less expensive than 120v models.
You'll probably need a ground rod driven since it's a separate building.

OR

Run a 20A MWBC (12ga H/H/N/G) to a double-pole switch as a disconnect. Almost as much power, but with less hardware.
 
  #5  
Old 12-04-12, 10:37 AM
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Adding to what has already been said,

What type of wire is recommended for the job?
THHN/THWN - the W shows that it is rated for wet locations.

Is the plan to bury the conduit buried at 18" compliant with national code?
Yes.

Does code require irrigation lines to be run a certain distance away from the electrical conduit?
Yes, particularly if they are running parallel to rach other or, especially, sharing a trench. Your plan to have them cross at right angles with 18" of vertical separation and the water lower than the power is fine.

Answers to questions you didn't ask:

I would run the power in 3/4" pipe That's plenty large enough, even if you pull 4 #10 wires for a 30A 240V subpanel.

I might install 2" conduit for the communication cables. Communication cables, being less sturdy than electrical conductors, need a really smooth pull with lots of room and big, sweeping bends. If you have to move the second conduit to be next to the power pipe and lower than 12" in order to accommodate the 90s, do that.

Many jurisdictions limit the total bends between boxes to 270[SUP]o[/SUP], especially for comm cables. It sounds like you'll be OK with that.

Install the conduit with the bell ends toward the end you will feed from and the straight ends toward the end you will pull from.
 
  #6  
Old 12-07-12, 09:14 AM
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We'll see how this goes

Thank you all for your comments thus far. Your guidance and direction is greatly appreciated.

After finishing with a few remaining Christmas light strands to hang tomorrow morning, I'll drop in the conduit and start fishing the lines. I almost certainly will have a few questions when I get to hooking things up at the main panel, so I'll likely return with some more questions (and pictures, of course).
 
  #7  
Old 12-07-12, 10:36 AM
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Put a length of nylon masons twine in the conduit as you make it up. No fishing. Just tie a steel nut or fishing lead sinker to the end and drop it down each length of conduit as you lay it in.
 

Last edited by ray2047; 12-07-12 at 12:52 PM.
  #8  
Old 12-07-12, 12:00 PM
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If you also add twine or poly electrician's "fish line" to the set of wires in the conduit as you pull them in, that will bee there to facilitate any changes in the future.

We'll be here for your termination questions.
 
  #9  
Old 05-29-13, 10:09 PM
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Project Resurrected: ready to resume work on electrifying the greenhouse!!!

I have a friend from church who is an electrical contractor and he donated some surplus electrical supplies to my cause. Those gifted materials have influenced my design and I am now ready to implement the following (which I submit for feedback):

I am supplying 30 Amps from the garage sub panel (Siemens WO816ML1125- see picture). The sub panel is supplied with 40 Amps, is rated for 125 Amps, and has availability for a Double-Pole Circuit Breaker.

I'll be putting in a Siemens QP 30-Amp Double-Pole Circuit Breaker (120/240V) in the garage sub panel.

I am running #10 AWG THHN/THWN (H/N/G) out to the greenhouse in the 1 1/4" PVC conduit that is already buried 18" underground and runs directly into the garage sub panel. (total run is right at 120 ft).

In the greenhouse I'll have a Safety Switch (GE TH4321 30A- see picture). I'll run down to 20 amps but can use recommendations on which breaker to use.

I'll run lighting and 3 electrical outlet in the greenhouse distributed from the safety switch. My final question is if it is ok to use 1/2 PVC conduit inside the greenhouse to distribute the #10 AWG THHN/THWN (H/N/G) conductors to the planned locations for the outlets and lights?

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  #10  
Old 05-29-13, 10:54 PM
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I am running #10 AWG THHN/THWN (H/N/G) out to the greenhouse in the 1 1/4" PVC conduit that is already buried 18" underground and runs directly into the garage sub panel. (total run is right at 120 ft).
What will the total load in your greenhouse be? You may need larger wire from the panel to the greenhouse to avoid having too much voltage drop.

My final question is if it is ok to use 1/2 PVC conduit inside the greenhouse to distribute the #10 AWG THHN/THWN (H/N/G) conductors to the planned locations for the outlets and lights?
The PVC conduit should be fine. You only need 12 AWG conductors for a 20A circuit and 14 AWG conductors for a 15A circuit such as lighting. IOW, I don't see any need to use 10 AWG wire beyond the safety switch.
 
  #11  
Old 05-30-13, 11:20 AM
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Max load will be 2000 watts.
 
  #12  
Old 05-30-13, 02:07 PM
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I may be interpreting incorrectly, but I think you mean to run 4 wires from the garage to the greenhouse (H/H/N/G) which will give you 2 circuits (technically one, multi-wire branch circuit).

You have two options:
1) Use a 20A double-pole breaker in the garage, then at the greenhouse, go through the disconnect, and then connect directly to lights/receptacles.

2) Use a 30A double-pole breaker in the garage, then at the greenhouse you'll need a subpanel with one or more 20A breakers. (A 30A feeder can't directly feed general purpose lighting/receptacles).


Once you're in the greenhouse, 1/2" PVC conduit is perfect. I would use 12ga THWN once you're in the greenhouse since the circuits will be protected at 20A. If you have extra, you could use 10ga, but it's overkill for those short runs.
 
  #13  
Old 05-30-13, 04:44 PM
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It is only 3 wires from the garage to the greenhouse (H/G/N), but after re-reading post #9 I believe that the confusion is in the garage breaker that I mention, which is actually a 30 amp single-pole breaker versus a 30 amp double pole breaker.

Do I not have the option to run 120V 30 amp from the garage to the safety switch?

And if OK I would just as well use the 10 AWG THHN/THWN for the runs to the outlets and lights, since I have about 200 extra feet left over!
 
  #14  
Old 05-30-13, 10:11 PM
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Max load will be 2000 watts.
That's 16.67 amps at 120V. To avoid having a voltage drop greater than 3% you will need to use 8 AWG wiring from the panel to the garage.

16.67 amps is 83.33% of the total non-continuous load capacity of one 20A circuit. You should be fine with the larger feeders.

And if OK I would just as well use the 10 AWG THHN/THWN for the runs to the outlets and lights, since I have about 200 extra feet left over!
You should have all of it left for running the wiring inside the garage.
 
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