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Wiring a Greenhouse

Updated February 21, 2017

Your greenhouse will need electricity whether you have a large one designed to raise hundreds of plants, or a small one to keep a few houseplants healthy through the winter. Vents, fans, automated watering systems and lights all require electricity. Larger greenhouses will require their own three-phase electrical system in order to be efficient. Smaller ones can be run from a line hooked into your home's breaker panel. Whichever system you run to the greenhouse can be wired and hooked into the electrical service with just a few tools and flexible conduit to keep your wiring safe.

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  1. Lay out your flexible conduit on the ground. Cut each piece 3 feet longer than you need it to be with your tin snips to compensate for adjustments.

  2. Push the tip of the fish tape through the conduit. Hold the tip of the fish tape against the side of the last 3 inches of ROMEX®. Attach the fish tape to the ROMEX® with electric tape.

  3. Pull the fish tape slowly through the conduit to draw the ROMEX® through the flexible tubing. Pull the ROMEX® 3 feet past the far end of the conduit and cut the wire with your tin snips.

  4. Remove the electrical tape to free the ROMEX® from the fish tape. Pull ROMEX® through every piece of flexible conduit that you will need for the job leaving 3 feet of ROMEX® hanging past both ends of each piece. Roll up your fish tape in its housing and store it for future projects.

  5. Mount your switches, fixtures and outlets to the exposed studs in your greenhouse. Use the Phillips-head bit on your drill to drive a galvanised screw through each of the retaining holes in every piece you wish to attach.

  6. Disassemble each of the fixtures and slide the end of the ROMEX® through the knockout hole in the back of the junction box. Pull the wire until the conduit is secure in the clamp mounted on the outside of the junction box. Tighten the retaining screw on the clamp with your screwdriver to lock the fixture in place.

  7. Slit the rubber armour on the outside of the ROMEX® with your razor knife. Pull the sheathing back and trim off the excess. Snip each wire to fit inside of the box and strip the individual wires with your wire stripping tool.

  8. Loosen any brass retaining screws on the side of the body of the inner workings of the fixture. Wrap the stripped end of each black wire around its own brass retaining screw. Tighten the screws to hold the wires in place.

  9. Loosen the silver retaining screws on the side of the fixture. Wrap the stripped end of a white wire around its own silver screw. Tighten the screws to hold the wires in place.

  10. Connect the bare ground wires to the grounding screw in the back of the junction box. Reassemble the fixture being careful not to damage the wiring.

  11. Check the breaker box in your house. Be sure that the breaker hooked to the electric wires running to your shed is turned off. Strip the end of the black and white wires on the ROMEX® running to the shed.

  12. Hold the white wire running to the shed with the white wire running from the shed. Twist a wire nut onto the two wires to bind them together. Wrap electric tape around the wire nut and 6 inches up the wires to complete the splice.

  13. Connect the black wires and ground wires at the main junction. Attach any other splices necessary inside of the greenhouse. Turn on the breaker in the house and flip each switch in the greenhouse to check every circuit.

  14. Tip

    Some greenhouses may have PVC, composite, or metal wall supports. Use the proper fastener for the job when attaching conduits and fixtures to your greenhouse.


    Work gloves and safety glasses are required when working with hand tools. Be sure that everyone is aware you are working on electrical circuits. Tell everyone on the property that they may not touch the breaker box until your project is complete.

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Things You'll Need

  • Flexible conduit
  • Tin snips
  • Fish tape
  • Electric tape
  • ROMEX®
  • "C" Brackets
  • Drill with Phillips bit
  • 1 1/2-inch galvanised screws
  • Fixtures, outlets and switches
  • Screwdriver
  • Razor knife
  • Wire stripping tool
  • Wire nuts
  • Work gloves
  • Safety glasses

About the Author

After learning electronics in the U.S. Navy in the 1980s, Danny Donahue spent a lifetime in the construction industry. He has worked with some of the finest construction talent in the Southeastern United States. Donahue has been a freelance writer since 2008, focusing his efforts on his beloved construction projects.

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