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240 volt vs 120 volt

Posted by woodturner79 (My Page) on
Mon, May 7, 12 at 9:07

I got a new bandsaw. The motor can be wired to run at either 120v or 240v. My friend told me I should wire it 240 because the motor will start and run better.
I realize at 240v it will pull less amps, but will it really be beneficial in any other way? Will it really run better at a higher voltage?


Follow-Up Postings:

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RE: 240 volt vs 120 volt

How large is the motor(horsepower on the motor nameplate) and what type motor?

Full size bandsaws typically use an induction motor int eh1 to 1.5 horsepower range.

Operation would be exactly the same IF the voltage does not change under start-up and running.

Motor start-up is the usually the issue.
The motor pulls far more current briefly as it tries to come up to speed,and this results in more voltage drop in the wires feeding the motor, the centrifugal switch contacts, and increased heating of the start winding.

On 240 V the motor will come up to speed faster with about half the current needed at 120 V.


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RE: 240 volt vs 120 volt

It would only be a factor with heavy use. If my shop didn't already have a 240 outlet, I wouldn't rewire my shop to provide one.


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RE: 240 volt vs 120 volt

It's a 1 HP motor. I'm not sure what you mean by type but it has a large capacitor on the motor that I was told helps it on starting?
wiring it for 240 is not an issue at all. It only involves changing some wires in the junction box on the motor. I have to run a new circuit for it anyway and have no problem putting it at 240. I just wondered if it would be beneficial at all and really help it to run better.


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RE: 240 volt vs 120 volt

"a large capacitor on the motor that I was told helps it on starting? "

Sounds like a standard 1-phase induction motor.

If you look on the nameplate of the motor it should have a kV-A locked rotor code letter.

This is used to estimate the starting current the motor uses, since when power is first applied it is at locked rotor (not-turning) conditions.

Tge full load current is in table 430.248.

A 1 HP motor on 115 V is 16 amps, and on 230 V is 8.0 amps.

Table 430.7 is the locked rotor code letter table.
It gives kV-A per horsepower.

The lowest value is 0-3.14 kV-A per horsepower, or 27.3 amps on 115 V, and 13.7 amps on 230 V.

Motor circuits do not follow the same rules as general purpose branch circuits, but a different set of rules in Article 430.


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RE: 240 volt vs 120 volt

The current demands to run the motor are roughly half at 240 than at 120. Less current for a given wire size means less voltage drop. Voltage drop can be a problem (can't say if it is in this situation). If you're going to run a new circuit, I'd certainly put in 240. It will be more flexible in the long run.


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