Converting a 120 Volt Motor to 240 Volts
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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.
Dave’s Reply:
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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Don, there are two problems here. One with the frequency difference and another with the voltage difference. Lets start with frequency: It is unlikely that you can convert the motor from 60 Hz to 50 Hz unless the motor nameplate specifies that it was already constructed to handle this frequency range. The 50 Hz European utility frequency is actually less efficient than the 60 Hz American utility frequency. This means that motors built for European systems must generally contain thicker gauge windings than an equivalent American motor in order to attain the same level of thermal performance. In other words, if your motor was built for the American 60 Hz standard, it likely has thinner motor windings, which could overheat if used on 50 Hz power. Now for the voltage problem: There are a lot of countries in Europe and they sometimes differ but in general they run on 230V per leg, where as America runs on 120V per leg and 240V when 2 alternating legs are used in combination. In a conversion from an American 120V to an American 240V system, you replace the neutral with a 2nd hot leg. In a conversion from an American 120V to a European 230V system, you still have just 1 hot leg, –but it would just carry more voltage, which the motor wires may not be rated to handle. Performing this conversion is ill advised.
Hi John,
Typically the voltage of these types of motors cannot be changed unless it is specifically stated on the label. However you may want to contact the manufacturer and see if they recommend a voltage converter that may be used to change the voltage from 240 to 120.
I hope this helps you,
Dave
I bought 2 ALECO DRYWALL SANDERS from a source online. They both have 120 volt electric motors. Can these motors be changed to 240 volts as I live in New Zealand where our country is 240 volts. I look forward to hearing from you.
Kind Regards,
John
Hi Don
It would be very helpful for you to provide the Brand, Model, and the nameplate information from this electric motor in order to see what different wiring configuration are allowed.
Dave
Ask the Electrician:
I have a 700 hp 900 rpm 4999 volt electric motor (3).
It is 120 v 60HZ.
I would like to change it to 220 Volts 50HZ?
Is it possible to begin with?
Is it fairly simple(less expensive)?
Is it very time consuming(More expensive)?
How does one do it?
Much Appreciated
don julien