How to Wire an Intermatic T104 Light Timer for 277V

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An Intermatic T104 light timer can operate a 277-volt light system.
An Intermatic T104 light timer can operate a 277-volt light system. (Image: Ryan McVay/Lifesize/Getty Images)

Industrial and commercial buildings often use 277-volt lighting systems in their parking lots and walkways. The Intermatic T104 has a 277-volt option designed for this application. Large buildings derive 277-volts from a 480-volt three-phase power source. A 480-volt three-phase power source has three conductors, the phases, and sometimes a neutral. A 277-volt electrical circuit uses one conductor and a neutral, which makes it a single-phase electrical circuit. An Intermatic T104 light timer uses a clock motor to turn the timer dial. Lugs on the timer dial operate the T104's switch.

Things You'll Need

  • Wire strippers
  • Slotted screwdriver

Turn off the lighting system's circuit breaker. If the lighting system contains more than one circuit, turn off all lighting system circuit breakers.

Identify the wires entering the Intermatic T104 light timer. A three-phase system uses color-coded insulation on its wires. In the United States, the conductors use brown, orange and yellow insulation on 277/480 volt systems. The neutral uses white insulation. The ground uses either green or green with a yellow stripe.

Strip 1/2 inch from the six insulated wires entering the T104 with wire strippers. Both wire sets contain three insulated wires: one conductor, one neutral and one ground.

Loosen the T104's terminals labeled "A," "1," "2" and "3" with a slotted screwdriver. Each terminal has its label printed on the timer above the terminal screw.

Move the T104's motor wire from the terminal labeled "3" to the "A" terminal. Tighten the "3" terminal's screw with the slotted screwdriver.

Slip the ends of the neutral wires from the power supply and the lighting system into the T104's "A" terminal with the motor's wire. Tighten the "A" terminal screw.

Slip the end of the power supply's conductor wire into the T104's terminal labeled "1." Tighten the terminal screw with the slotted screwdriver.

Slip the end of the lighting system's conductor wire into the T104's terminal labeled "2." Tighten the screw with the slotted screwdriver.

Route the lighting system's and the three-phase power supply's ground wire to the Intermatic T104's green ground screw, located on the plate holding the timer dial. Keep these wires away from the other wires and the the wire terminals. Wrap the ground wires around the ground screw. Tighten the ground screw with a slotted screwdriver.

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