Two-speed electric motors operate in one of two ways; two separate windings designed to rotate the motor at two different speeds, or inbuilt resistors which alter the voltage supplied to windings. However, the wiring to the motor is the same; it has four terminals. One terminal is the ground, another “common” and the third and fourth are for fast and slow speeds. Wire a single pole, double throw (SPDT) switch into the circuit between the motor and the wall socket and you can change the speed of your two-speed motor.
Strip 2 inches of plastic off the opposite end of a prewired plug using wire strippers The wire needs to be nonmetallic AWG 14. This reveals the three internal wires.
Remove ¼ inch of plastic off the ends of the three colored wires using wire strippers. The colored wires are green stripped, gray/white and red/orange, but sometimes black. The colors mean ground, neutral and hot respectively.
Remove the cover from the SPDT switch using a screwdriver. Locate the two terminal blocks. One has three terminals, the other four. The three terminals connect to the wire from the plug while the four terminals connect to the motor.
Loosen the screws on the three pin terminal block using a screwdriver. Connect the green stripped wire from the plug to the terminal labeled “Gnd” or “T” and tighten the screw. Connect the white/gray wire to the terminal labeled “Neu” and then the red/orange or black wire to the terminal labeled “Hot” or “Com."
Cut four strips of AWG 16-gauge wire long enough to reach between the SPDT switch and the motor. Label the strips "A" through "D" using a marker pen. Remove ¼ inch of plastic off the ends of the four wire strips.
Loosen the four screws on the screws on the four pin terminal block. Connect the wire labeled “A” to the terminal labeled “A” or “1” and tighten the screw. Connect the wire labeled “B” to the terminal labeled “B” or “2” and tighten the screw. Connect the wire labeled “C” to the terminal labeled “Gnd” or “T” and tighten the screw. Connect the wire labeled “D” to the terminal labeled “Com” and tighten the screw.
Connect the opposite of the wire labeled “C” to the ground terminal on your motor. Connect the opposite end of the wire labeled “D” to the terminal labeled “Com”, “Hot” or “Pos” on the motor. Connect the opposite end of the wire labeled “A” to the terminal labeled “Slow," “Low” or similar. Connect the opposite of the wire labeled “B” to the remaining terminal.
Replace the cover on the SPDT switch and tighten the screw to hold the cover in place. Ensure the switch is in the “off” position. Insert the plug into the wall socket. Turn on the switch to the first position and the motor turns slowly. Move the switch to the second position and the motor turns fast.
Things You'll Need
- Single pole, double throw (SPDT) switch
- Prewired plug (nonmetallic AWG 14)
- AWG 16 gauge wire
- Wire strippers
Stephen Benham has been writing since 1999. His current articles appear on various websites. Benham has worked as an insurance research writer for Axco Services, producing reports in many countries. He has been an underwriting member at Lloyd's of London and a director of three companies. Benham has a diploma in business studies from South Essex College, U.K.