Greenhouse wiring

Thread Starter

Cajunbubba

Joined Dec 25, 2009
17
I am wiring up a greenhouse that we built. I have installed 2 - 20 amp GFCI breakers and will use 12 guage wires. Because everything is in conduit I am trying to minimize wires. Here are my circuits:
1- recepticles on a timer switch for grow lights (about 1000 watts)
2 -(a)Exhaust fan and shutter motoers on a thermostat and reosatat (about 500 watts) & (b)additional recelpticles for possible heating pads

I am in the process of planning my wire pulls. I am using 3 wires Black (hot), White (neutral), Green (ground).

Main conduit runs overhead and drops down to various recepticles and stuff.

I would like to splice off the green and whites and run down to the recepticle but not back up to the main conduit. The black will go down and back up. (hopefully I have painted a picture). My qusetion is this going to create an inbalance for mu GFCI?
 

SgtWookie

Joined Jul 17, 2007
22,230
I really don't like to be critical, but...

Your project really requires the on-site scruitiny of a professional electrician.

I am NOT a professional electrician.

Furthermore, no professional electrician worth his or her salt would be able to give you proper advice remotely.

You need a professional electrician to look at your requirements and to keep you safe.
 

Thread Starter

Cajunbubba

Joined Dec 25, 2009
17
ok here is a basic view of what I want to to do. These are single 12 gauge wires. Seeing that I am proposing different lengths and junction points will this cause problems with my 20 AMP GFCI?
 

Attachments

Wendy

Joined Mar 24, 2008
23,415
The GFI is basically a circuit hanging off your wiring, it shouldn't have a problem, as long as you aren't trying to use it to feed the other circuitry. If you are, don't. Use a GFI as if it were an outlet for each outlet.

This is the image you posted, cropped to fit.



You should also be aware which pin is hot, and which is neutral, it is important.



For what it's worth, I agree with Wookie completely, this is not a job for an amateur.
 

Attachments

jpanhalt

Joined Jan 18, 2008
11,087
One thing to consider is how you are going to tap into the neutral and ground, if that is really what you mean to do. Remember that such taps must be in an accessible box.

Many electricians will simply run all three wires to the receptacle box (use a sufficiently large one) and make the taps or pigtails there. Be sure to consider that the box, if metallic, will also need to be grounded.

John
 

Thread Starter

Cajunbubba

Joined Dec 25, 2009
17
Thanks folks. The circuit diagram I supplied is fed from a 20 Amp GFCI breaker. the pigtails to be wired to be nutted at junction boxes. There will be about 8 receptacles on this circuit. I will have another circuit just like it on another 20 AMP GFCI breaker. Can I use common neutral throughout?
 

Wendy

Joined Mar 24, 2008
23,415
NO!

The GFI is a circuit. It monitors both hot and neutral, and hot and neutral are the outputs of the GFI. The GFI will turn the hot lead off if there is a problem, and possibly the neutral (not sure about that one, but a little research says it is probable).

http://en.wikipedia.org/wiki/Residual-current_device

This is why you need a professional, cutting corners can kill in this case.
 
Last edited:

jpanhalt

Joined Jan 18, 2008
11,087
Get Wiring Simplified, 42 edition (2008) for $5.90 at your big box store. See page 116, Figures 10-13, 10-14, and 10-15. They explain why you cannot use a "3 wire" circuit based on what you have described. However, if you modify the circuit to use both poles/legs of a 220V household (USA) supply, then you can use a 3-wire circuit.

In brief, using two live wires and one neutral from a single pole, the neutral potentially carries the combined currents of both live wires. Could you increase the gauge of the neutral appropriately and do it from just the one leg? I don't know. That is a question for a qualified electrician. If you use both legs of the 220 service, then the neutral cannot carry more than either leg (see: Figure 10-15) because of the phase difference.

I think everyone here has given good advice and many, if not all of us have done household or limited commercial wiring. For simple wiring tasks, I believe a homeowner should be allowed to it, if he or she follows the simplified code to the letter. If you want to deviate from that, then you need an expert.

John
 
Last edited:
One thing to consider is the temperature expected.
I wasn't able to find your location, but summer heat may cause trouble with the
wires.
Heat can degrade the insulation over time.
That is some of the things covered in NEC 2008, or more recently NEC2010 if it is out.
NEC is the National Electric Code, also called NFPA 70 (National Fire Protection Association) This assumes you reside in the USA.
There are different insulation grades for different uses and areas of installation.
There may also be directions for installing GFI.
In USA, your local community college may have a class in it.
 

Thread Starter

Cajunbubba

Joined Dec 25, 2009
17
location is western washington state. So I do truly need to come out of the back of each GFCI breaker with it's own hot & neutral as opposed to what I have sketched here (not I left the ground off to simplify drawing).
 

Attachments

maxpower097

Joined Feb 20, 2009
816
I really don't like to be critical, but...

Your project really requires the on-site scruitiny of a professional electrician.
+1 I've worked in environments like this and you have to be extra extra careful in your wiring. If you don't know exactly what your doing call in a pro. Last thing you want is to come home to a fire or get electrocuted standing a puddle. Which does happen with 1000w + lights. Also make sure you have surge protection from a lightning strike, lightning + 1000w light = hand grenade.
 

Wendy

Joined Mar 24, 2008
23,415
OK, here is his drawing...



I've basically stated my case. Please have a professional review your work when you're finished.


.
 

Attachments

Top