What's the difference between 115 and 230 volts?

I purchased a used tablesaw that has the option to wire it for either 115 or 230 volts. My landlord, who pays the electric bill, says that wiring it for 230 volts will use more electricity. What are the pros and cons for either voltage?
—Rick España, Cherry Valley, Calif.

Your tablesaw's motor uses the same amount of electricity (measured in watts) regardless of the voltage, Rick. If you look at the plate on your saw's motor, similar to the one below, you'll see that as the voltage doubles, the saw uses half as many amps. For example, this contractor-style saw drops from 18 to 9 amps as the voltage doubles. Either way you multiply the combinations—115 volts times 18 amps or 230 volts times 9 amps—the power consumption remains 2,070 watts.

So why wire for 230 volts? Look at those amp numbers again. If you're pulling 18 amps on a 20-amp circuit, there's the chance of tripping a circuit breaker if your saw encounters an especially heavy load, or at startup, when it draws a brief surge of power. By switching to 230 volts, you relieve that strain on the circuit, doing you and your landlord a favor.

If your saw needs an extension cord 50' or longer, that's another reason to opt for 230 volts. The higher voltage encounters less resistance within the cord, delivering more power to your saw.

As for cons, a 230-volt outlet should be wired by a professional, and the breaker box may not have space to expand.