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Joined: Nov 2004
Posts: 24

I have a couple of American power tools that I am running off the standard 110 volt / 50 hz site supply in the U.K. and want to know if I am doing any harm.

I looked at the plates on some of my U.K. tools and it says 110 volt / 50 - 60 Hz.

One American tool says 120 volt 50 - 60 Hz.

The other American tool says just 120 volt 60 Hz.

As I understand it the frequency affects the speed of a motor so how can a tool be rated at either 50 or 60 Hz?

Am I wrong in thinking that the 10 volts difference is not a real problem?


David Lloyd

Joined: Dec 2001
Posts: 2,495
There are synchronous and asynchronous motors. A synchronous motor's speed will be affected by the frequency. An asynchrous one won't care too much. And most tools have asynchronous motors. The 10V difference won't do much harm I think. After all some stuff works on a low 220V system as well as on a British 240V...

Joined: Nov 2004
Posts: 24

Is there a way to determine which type of motor a tools has?

I see long leads all over building sites so I imagine no tool gets the full 110 volts anyway due to voltage drop.

I imagine the best thing for me to do is keep he leads as short as possible and use as heavier guage as possible, or am I just being too cautious?

David Lloyd

Joined: Dec 2002
Posts: 1,253
djk Offline
It shouldn't be a huge problem 110V 60Hz is well within the tollerance of any US product. The old official rating was 110V and I'm sure that there are plenty of outlets in the US and Canada that supply closer to 110V than 120V.

If the frequency isn't an issue it work just fine.

The only thing to note is that the transformers used in the UK and Ireland provide 2 X 55V lives out of phase. So, you've 110V between the two lives and 55V between either terminal and ground. This reduces the potential for electric shock.

It's really not a problem, however just be aware that your powertool could be live with 55V even when the switch is in the off position.

Joined: Nov 2004
Posts: 24

The one tool in question is marked 120 volts 60 Hz.

How do I determine if the frequency is an issue or not?

I'm confused about the tool being live with 55 volts with the switch even in the off position. I didn't get a shock, burn, or tingling sensation yet :-)

David Lloyd

[This message has been edited by davelloyd (edited 11-14-2004).]

Joined: Apr 2002
Posts: 2,527
Most US motorized power tools have universal motors with a wound armature. Those should run OK, but maybe at a little lower speed from 10 volts under [and not 10 Hertz under.]

120V resistive heating devices at 110 V would dissipate 84% (110/120)² of nameplate wattage.

[This message has been edited by Bjarney (edited 11-14-2004).]

Joined: Aug 2001
Posts: 7,520
Hi David,

I've also run U.S. power tools from the 110V site transformers as well, and never experienced any problems.

The "universal" motor is the one you will find in just about all hand-held power tools, and the frequency difference on these is of no great significance. In fact some universal motors are designed to be run on DC as well as AC (many older domestic vacuum cleaners had such a motor, for example).

These universal motors are all of the asynchronous type, meaning that the rotor speed is not locked to the supply frequency. Synchronous motors are found in such items as electric clocks (mechanical type), small fans, and older style record players and tape recorders.

I'm confused about the tool being live with 55 volts with the switch even in the off position. I didn't get a shock, burn, or tingling sensation yet
Don't worry, you won't be zapped! [Linked Image]

The 120V you get from a wall outlet in the United States has a "hot" line and a neutral, just as a 240V British socket provides a live and a neutral. In both cases, the neutral is grounded (earthed) at source, so there is no voltage between it and the earth. The live/hot line is then at 120 or 240V with respect to earth.

The British 110V site transformer has a transformer winding with the center-tap earthed. That means that the two supply lines are both "hot" -- There is 110V between the two wires, but only 55V between either wire and earth. The idea is that the reduced voltage to earth improves safety (and we've had debates about that in the past!).

In practice, as far as your portable power tools are concerned, that's of no consequence so long as you don't go poking around inside them with the power connected.

Joined: Nov 2002
Posts: 456
Most power tools have both power lines switched anyway.

Joined: Nov 2004
Posts: 24

Thanks for the help.

I contacted Skill and this is what they said -

"Dear David,

Thank you for writing. The motor we use is neither synchronous nor asynchronous. It is a Universal Series motor. Since you have actually reached Skil USA customer service, if you have additional questions, please contact Skil UK through the following link"

I'm still a little confused though as there seems to be three types of motor - synchronous, asynchronous and universal.

David Lloyd

[This message has been edited by davelloyd (edited 11-19-2004).]

Joined: Aug 2001
Posts: 7,520
It sounds as though Skil customer service is confused, for the universal series motor is a type of asynchronous motors.

All motors must fall into the overall synchronous or asynchronous categories. Either the design of the motor synchronizes its speed to the supply frequency or it doesn't. The universal series type doesn't, therefore it is, by definition, an asynchronous motor.

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