How to Hook a Portable Generator to a Furnace

Written by jerry walch Google
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How to Hook a Portable Generator to a Furnace
Use silicon caulk to prevent water from seeping behind the device box and entering the wall. (Jupiterimages/ Images)

Connecting a portable generator to a gas or oil-fired furnace is a relatively easy task but it will involve running ROMEX® cable, installing a double-pole, double-throw safety switch and a weatherproof outdoor male receptacle. This is a project that any handy person with minimal experience with electrical circuitry can complete successfully and safely. Being able to connect your portable generator to your furnace will ensure that your home will be comfortable even during a prolonged power outage.

Skill level:

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Things you need

  • Weatherproof, surface mount device box with mounting hardware
  • Silicon caulk
  • Caulking gun
  • Weatherproof, receptacle cover
  • Three ROMEX® cable connectors
  • 12/3 with ground ROMEX® cable
  • 3/8-inch drill-driver
  • Spade bits
  • Hammer
  • Cable staples
  • Screwdriver
  • Cable cutter
  • Razor knife
  • Wire cutters
  • Wire strippers
  • Long nose pliers
  • Double-pole, double-throw, centre-off, 120-volt, 20-ampere toggle switch

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  1. 1

    Locate a spot on the outside of your home close to the furnace location. Drill a 1-inch hole through the wall into the basement.

  2. 2

    Install a run of ROMEX® cable from the hole in the wall to the location of the furnace safety switch. Extend 12 inches of cable outside the house. Secure the cable to the sides of the ceiling joists at four and one-half foot intervals with cable staples. You may also run the cable perpendicular to the joists by passing it through 3/4-inch holes drilled 1 1/4 inches from the nearest edges of the joist. This setback is required by the National Electrical Code. Secure the cable ends within 12 inches of the safety switch and the hole in the wall.

  3. 3

    Install a cable connector in the back of the weatherproof box. Install the cable through the back of the device box. Push the cable through the cable connector until the end of the cable extends 6 inches beyond the front lip of the box. Fasten the device box to the wall's exterior surface using the appropriate screws supplied with the box.

  4. 4

    Using the razor knife, remove the outer jacket from the cable at the outlet/device box end. Remove 3/4 inches of insulation from the ends of the black and the white wires. Form a loop in the ends of the stripper wires using the needle-nose pliers. Place the loops on the black and the white wires in a right hand direction around the brass and silver coloured screws on the receptacle. Place the bare copper wire around the green screw in a like manner. Tighten the screws down on the wires.

  5. 5

    Install the receptacle in the box using the two 6/32 screws provided. Install the weatherproof cover on the box. Run a generous bead of silicon caulk around the box where it makes contact with the wall.

  6. 6

    Locate and turn off the circuit breaker in the breaker panel. This protects the furnace circuit. Remove the cover to the old safety disconnect switch and remove the switch from the box. Disconnect all the wires from switch. Install a cable connector in the side of the box and install the end of the new cable in the box. Remove the cable jacket and strip the wires as you did at the weatherproof outlet box.

  7. 7

    Connect the black wire and the white wire to the bottom brass and silver screws on the two-pole, double-throw, centre-off switch. Connect the wires from the breaker panel to the top screws on the switch and the wires going to the furnace to the centre terminal screws. Connect the bare ground wires to the green screw.

  8. 8

    Install the new switch in the box and replace the cover plate. Place the safety switch in the up position, connecting the furnace to the breaker panel.

  9. 9

    To connect your portable generator, turn the safety switch to the bottom position and plug the male-female jump lead that came with your generator into the weatherproof male receptacle and into your generator's 110-volt outlet.

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