How to Provide Power to Air Handler Heat Strips

Calculating Your Wire Length and Size

• 1

  Consult the specifications sheet in the documentation of the heat strip for the maximum current rating in amps. Most heat strips are anywhere from 30 to 60 amps. If the run to the heat strip is over 100 feet, increase the wire to the next larger size to allow for voltage drop. The amp ratings in the material list are taken from the 2008 National Electrical Code 310.16 using the 60-degree temperature rating as per NEC 334.80 concerning Romex wire.

• 2

  Measure the distance between your electrical panel and the air handler to figure out the length of wire needed and add 15 to 20 feet to allow for routing around trusses, a 6-foot piece of wire to feed the heat strip from the disconnect and the drop into the electric panel from the attic.

• 3

  Check in the attic where the wires will be run and add more to the wire length if you have to go around any obstructions. Purchase the wire according to the amperage in the material list. Be sure that the two-pole breaker you purchase matches the amp rating of the heat strip, and the brand and model of the electrical panel.

Installing the Run to the Air Handler

• 4

  Turn off the main breaker and open up the electrical panel by removing its dead front cover. There are concentric knockouts at the top of electrical panels that can be removed with a screwdriver and needle-nose pliers. Knock out a 3/4-inch hole. Insert a two-screw 3/4-inch connector into the top side of the hole and thread on the nut that holds it in place from inside the panel. Leave the two screws very loose for now.

• 5

  Cut a hole in the drywall with a drywall saw above the electrical panel inside the garage to allow access to the inside of the wall where the wire from the attic will come through. This will also give you access to secure the wire going into the panel within the 12 inches required by NEC 334.30 and 334.17.

• 6

  Pull your wire from the air handler to the electrical panel. Stay at least 6 feet away from any attic access, otherwise it will be necessary to protect the wire from being trampled when entering the attic. You may need to drill a hole in the top plate above the electrical panel using a drill and 3/4-inch auger bit if there isn't already one there. If you have to drill a hole be sure the main breaker is off to avoid being electrocuted, in case you accidentally hit another wire while drilling. Being very careful not to hit any of the electrical wires passing through the top plate, drill the hole.

• 7

  Feed the wire through the hole from the attic and pull it into the panel through the connector you installed earlier. Pull at least 2 feet of wire into the panel. Using a razor knife strip off the wires' vinyl coating, being very careful not to nick the insulation on the conductors inside the sheath. Leave at least 1/4 inch of the vinyl insulation visible inside of the panel per NEC 314.17. Tighten the two screws on the connector your wire went through to enter the panel. Secure the wire with a J nail within 12 inches of the panel.

• 8

  Mount the disconnect within eyesight of the air handler for the purpose of turning off the power for servicing. Screw the disconnect into one of the wood trusses, with the 1 1/2-inch wood screws, near the unit. Knock out two 3/4-inch holes from the concentric rings in the bottom or back of the disconnect for the wires to enter the box. Insert two 3/4-inch Romex connectors into the holes you knocked out, with the two screws on the outside of the disconnect. Thread the nuts onto the connectors from inside the disconnect box.

• 9

  Pull most of the slack out of the wire coming from the panel box. You will need to run another 6-foot piece of wire from the disconnect into the the heat strip without routing it over the walkway around the unit. Cut the wire coming from the electrical panel so that at least 9 inches will be inside the disconnect, with enough slack to staple it within 12 inches of the box. Insert the two wires into the disconnect through the connectors. Strip the vinyl insulation off of the wires with your razor knife, leaving 1/4 inch visible inside the disconnect. Strip 1/2 inch of insulation off of the individual wires with your razor knife, being careful not to nick the wires.

• 10

  Secure the wires with a J nail within 12 inches of the disconnect. Connect the non-insulated wires to the ground lugs in the disconnect. Attach the two black wires from the electrical panel to the connections on the side marked "line" in the disconnect. Attach the two black wires going to the heat strip to the connections on the side marked "load."

• 11

  Pull the cover off of the air handler where the connections for the heat strip are. There should be a knockout in the unit for the wire from the disconnect. If there is no knockout you will have to drill a 3/4-inch hole in the unit with a 3/4-inch unibit near the heat strip connections, not in the cover. Insert the last Romex connector into the hole, with the screws on the outside. Thread the nut onto the connector from the inside of the unit. Strip the vinyl off the wires, leaving 1/4 inch of vinyl visible inside the unit. Strip 1/2 inch of insulation from the ends of the insulated wires.

• 12

  Connect the non-insulated wire to the ground connector inside the heat strip. Connect the black wires to the terminals marked L1 and L2 on the heat strip. Secure the wire within 12 inches of the connector with a J nail outside of the air handler. Replace the cover.

• 13

  Strip 1/2 inch of insulation from the ends of each wire at the breaker panel. Connect the bare wire to the ground bus in the electrical panel where all of the other bare and green wires are connected. Find two empty spaces side by side in the panel and insert the breaker by hooking it into the rail and plugging it into the bus. Attach the two black wires to the breaker's two terminal screws with your allen wrench or screwdriver. Replace the dead front cover. Turn the main breaker back on.