Converting a 120 Volt Motor to 240 Volts
How to Convert the Electrical Circuit Voltage for a Motor: There are multiple problems here. You and the electrician did not discuss exactly what the 240 volt outlet would be used for. This is a big mistake, and I’m amazed that the electrician did not ask you what the circuit would be used for.© By: Dave Rongey
Converting the Electrical Voltage of a Motor
Electrical Question: I have an old Craftsman table saw that can run on either 120v or 240v with a minor change within the motor, which has three input wires – a ground and two lines. For some years, I’ve operated it at 120v, but it lacks the power to rip certain hardwoods.
- Recently, in conjunction with another project, I asked a licensed electrician to install a 240v outlet in my garage, but wasn’t specific about what I wanted.
- He installed a 4-wire outlet, and provided me with a matching plug, and I thought it would be a piece of cake to connect up the table saw motor.
- I bought a double-pole, single throw switch, which has two terminals marked Load and two marked Line.
- After checking the switch with my ohm meter, I connected the switch and the motor but found that when I turned the switch on, the circuit breaker blew.
- I ran the black wire from the plug to a Load terminal, then a wire from the corresponding Line to the motor, and similarly for the red wire from the plug.
Clearly, I’m missing something, but what?
Background: Michael, a Handyman from Sherwood, Oregon.
Thanks for your electrical wiring question Michael.
How to Convert the Electrical Circuit Voltage for a Motor
- There are multiple problems here. You and the electrician did not discuss exactly what the 240 volt outlet would be used for. This is a big mistake, and I’m amazed that the electrician did not ask you what the circuit would be used for.
- Next – you are not understanding the meaning of Line and Load. Line is the incoming power side of the switch. Load is the load being placed on the Line, that being the table saw motor.
- A typical 240 volt table saw motor only requires three wires, two hots, one ground. The size of this required circuit will be determined by the horsepower size of the motor. Also, when changing the voltage from 120 to 240 volts, most motors require the internal wiring configuration to be changed.
- I would speculate that you have wired a direct short circuit configuration of hot to hot or a hot to neutral which is causing the circuit breaker to trip off.
- In summary, it would have been great if you would have shown the table saw to the electrician and allowed him to wire specifically, and provide the switch and motor connections.
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