Wire greenhouse subpanel


250ft from main panel in house to greenhouse out back. Greenhouse will have propane heater and one 120v outlet.

Today I dug 100 ft trench to the house 1ft deep. I put 1" and 3/4" conduit in the trench along with a 12AWG THWN solid copper wire (tracer). The 1" conduit will have a MDPE gas line, the 3/4" conduit will have THWN wire. I know MDPE can be direct burial but I like the idea of having it in 1" conduit just in-case.

I'm running 4 THWN conductors 10AWG. At the house, 10-3 NM-B will splice to the THWN in the LB as it exits the house. In the greenhouse I have a small outdoor rated 70A subpanel; 2 circuits.


1) Do I need a grounding rod at the sub panel? I know it should NOT get tied to neutral.

2) I will install 30A GFCI breaker in main panel, 1 pole or 2?

3) Can I install two 15A breakers in sub panel, each would be 120V?

4) The breakers in sub panel can be non-GFCI, correct?


Edit - Update

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That's an electrician job to me. I let my electrician do that part and supply the hardware for it. There are ways to wire a 240v panel and use as a 120v subpanel but to me it's an overkill on the panel hardware. One way I saw only used one side of the larger panel, another I saw was wired in a way that every other breaker gets used? But a whole house load center is not really appropriate for this green circuit subpanel or breaker box.

For larger systems and Grid-Tie what is usually used is about a 2 to 4 space 60 to 80 amp load center. At most, one that can take about 4 to 6 circuit breakers would be plenty of room for growth. Here's a link to one about like I am used to seeing used for our largest systems. See if you are looking to make that much power you would gop with a grid-tie and the excess would go to the main panel.

http://www.hardwarestore.com/pop-print/ ... odNo=41176

http://electrical.hardwarestore.com/14- ... 07096.aspx

But I would not put...

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sirvayr: Why not just ground the right bus bar in the subpanel to the box with a piece of wire, strap, etc?

Justin Stanton : what about running a grow room

jwsolarusa John: Thanks for sharing your video.
I just subscribe to your channel. Please checkout my channel and please subscribe and thumbs up

ke0kie: Great vid. Question. It looks your sub-panel only has a bus to attach breakers, no lugs to attach the feeder circuit. My sub-panel uses lugs to terminate the feeder hots, therefore I'm planning to install a disconnect box just before the sub-panel. My sub-panel is a detached building, and I did not want to have to go between buildings to resolve tripped breakers, turn power on/off etc.

Roy Kingsbury: thanks for your vids! i am building a 20'x30' garage and you have helped me a lot with the electrial

TheChosenOne: no one ever talks about what size wires or what

michael rodriguez: where the white tape on the subs neutral going to the...

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You have lots of input here, but if you are concerned with wiring this sub-panel up in accordance to the NEC (National Electrical Code), you probably need some better direction than these replies (no disrespect intended to the posters, but the NEC rules can be somewhat tricky).

Here are some things to consider:
1) Do you really need this sub-panel? If you have plenty of available breaker spaces in your existing panel, the only advantage in a sub-panel is to minimize wire runs for your branch circuits.

2) What types of loads will this panel service? Will your new loads overload your main service panel's capacity? If you are only adding general use lighting and receptacle loads (even HT equipment is generally considered general use), probably not, but you mentioned HVAC. To answer these questions you will need to do a load calculation for your service, which is tricky to do. If you are so inclined, a helpful website for doing this according to the 2002 NEC can...

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When adding a subpanel I know you are supposed to isolate the ground and neutral in the subpanel. My question is what exactly is the “electrical” definition of an isolated ground and neutral in the subpanel?

In the main panel the grounding bar is bonded to the box. Neutrals (white) and grounds (green) are terminated to this grounding bar. Okay, now I run 4 wires from the main panel to the subpanel. The white wire goes to the neutral lug in the subpanel and the green wire goes to the box. The neutral lug and the box are not bonded (no ground strap or screw from the neutral lugs to the box). Now my question is this…since the white and green originate from the same place in the main panel does this not defeat the effort to isolate them in the subpanel? In the subpanel you can put an Ohm meter across the neutral lug and the box and get a reading, as opposed to being open. Is this still considered being “isolated”?

When adding a subpanel I know you are supposed to isolate...

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So i am running a subpanel in my garage, from my meter/main panel.

The run is 325 ft. I was hoping to run 100A, but was told the maximum run on 100A (with 4/0 alu.) is 290ft.

So I will be running 80A.

to carry 80A 325ft, what size wire do i need?

I was told 4/0 aluminum... but that seems huge. I do not think the breaker in my sub will even take it?

any thought filled insight will get +K in appreciation.


as an update... this website http://www.vihon.com/Vihon_Calculato...alculator.html

using 24000 W (100A) and 325ft and allowable drop of 5% gave me a gauge of 0... which is way different than my friend's assessment of 4/0 (OOOO, or "four Aught") and that i could only run 80 amps on 4/0 if over 290 ft... any help clearing the fog would be...

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Installing an electrical system in a greenhouse isn’t for amateurs. There are many factors to consider, including size of operation, load demands, wire location and environmental considerations, to name a few. Growers must keep in mind immediate and future needs and prepare for emergencies when they arise. The first step is finding a qualified electrician who can be relied upon to get the job done right.

Choosing An Electrician

Depending on the type of greenhouse project, Tom Manning, a project engineer at Rutgers University’s New Jersey Agricultural Experiment Station in New Brunswick, N.J., says if a grower has worked with an electrician he is comfortable with that would be the first choice to consider.

“If the grower doesn’t know an electrician suitable for the project, there are two levels of competence a grower might look for,” he says. “Consider an electrician who has some experience or can provide recommendations for working on a greenhouse project. If...

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As the proud owner of a ca. 1825 farmhouse, I understand a lot of the challenges and adventures that come with playing "this old house", and it sounds like you have your share too!

That said, I have no idea what it might take to rework your plan to take power from the main panel instead of that unused two-wire ungrounded circuit. Any chance you could pull a new cable there with an equipment ground and maybe a bit more ampacity?

The lack of a ground at the point of hookup is definitely a problem and it all but guarantees that any "solution" you try will violate modern electrical codes.

I think I understand the ground rods providing some protection against lightning and other surges but not being conductive enough to create overcurrents that will trip a breaker (though surely strong enough currents to trip the GFCI I plan to place on the barn branch circuit).

Actually, equipment grounds have little or nothing to do with the operation of a GFCI. Because a...

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NOTE: The subpanel must be placed within 100 feet of the main electrical service panel, and between 5 and 50 feet away from the spa. All electrical connections must

be made in accordance with the wiring information contained in this manual and on the back of the field wiring access panel of the control box.

Refer to the wiring diagram below.

1. Connect the #8 AWG, WHITE [NEUTRAL] wire from the Neutral/Ground Bar on the main electrical service to the WHITE [NEUTRAL, Panel Neutral, Pigtail] of the


2. Connect the #8 AWG, BLACK [L1] wire from the main electrical service to the subpanel [terminal L1].

3. Connect the #8 AWG, RED [L2] wire from the main electrical service to the subpanel [terminal L2].

4. Connect the #10 AWG, GREEN wire from the Neutral/Ground Bar on the subpanel GRD.

5. Connect the #8 AWG, WHITE [NEUTRAL] wire from the subpanel to the Neutral terminal on the...

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Here I intend to give clear information on a number of basic house wiring issues that may be unfamiliar or confusing to the do-it-yourselfer. These certainly don't cover everything you might want to know. In what I say I am careful to qualify my statements if they have exceptions, using words like "usually" or "typically." If a practice is specified by the National Electrical Code I will tend to indicate this by "is to be," "should," or "must," and I won't talk that way if the matter is just common practice.

For problems with existing wiring, circuits, and connections, be sure to see my Main page. For issues about some particular appliances see this. To understand electrical terms see the Glossary. For wire ampacity and conduit capacity see SparkyJohn.

15-amp versus 20-amp
Main panel

Romex cables. Your wiring could be done with a conduit system or metal-sheathed cables, but in most places...

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Dig an 18-inch deep trench from the location where the wire will enter the house to the garage.

Use 1 1/4 inch PVC conduit for a 100-amp sub-panel or 1 inch PVC conduit if the sub-panel is 50 amps or less. Run the conduit from the garage to the main panel box. If concrete has not been poured in the garage, run conduit down into the ground on the inside of the garage. Use a 90 degree sweep connector, instead of a sharp 90 degree connector, to make it easier to pull the wire through. If the concrete is already done, run the conduit up the wall on the outside of the garage and use a PVC LB access fitting to go through the wall where the sub-panel box is to be mounted. Do the same at the main panel box.

Screw a piece of plywood that is 6 inches bigger then the sub-panel to the wall where the sub-panel is going. This is called a backer. Screw the sub-panel box to the center of the backer and connect the conduit to the sub-panel. Some local codes require the backer to...

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If the objective is to provide 120V receptacles and lighting only (i.e., no 240V equipment) without running new wiring, then yes, this is do-able assuming that branch circuit supplying the hot tub is Code compliant in the first place.

How this would be done depends on the specifics of the current installation; e.g., is it a 2-pole, 3-wire 240V branch or a 120V/240V 3-pole, 4-wire multiwire branch; ampacity, etc. Different tubs require different circuits.

Some of the advice that has been given on this thread is contradictory, and even I'm just some guy on the internet. Incorrect electrical installations can kill someone or burn down the house; this isn't just a matter of, say, a botched finish messing up the latest project. You might want to consult with a pro, or at least get a book and do some...

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