US 2x110 volt 60Hz the same as 220Volt 50Hz

The only safe thing to do is contact the manufacturer and ask them if the design will be harmed by 60 HZ.

I assume the 2 X 110 (actually 2 X 120 Volt) line you speak of here in the USA is single phase and not three phase.

Normal clothes dryer connections are 2 ea 120 Volt, plus ground. Those two legs are the two lines coming in from the service provider. Note also that US electrical is not 180 degrees (exact opposite) phase. Usually like 120 degrees, and can cause some loss of efficiency. Again, direct this info to the German manufacturer and ask if the equipment will be harmed by this setting.

US power is supplied as two 120+/- (sometimes called 110, 115, 120) volt lines with respect to neutral plus a ground. These two "hot " lines can be used as 220 +/- single phase as is done in ranges, dryers, and single phase 220 motors like your A/C compressor probably has. The main concern would be the frequency tolerance of the power supply and the voltage tolerance of the powered circuits. A 50Hz (design point) transformer would have somewhat higher impedance at 60Hz which may result in somewhat lower output voltage or regulation concerns. (It can be more of a problem to use a 60Hz component with 50Hz.) Many transformers are rated for a range of frequencies, implying that whatever temperature or current variations might be involved are within their capability. You could ask your manufacturer bluntly if they would predict damage if operated on 60Hz. I suspect not, but they should know. JMHO :)

I agree with Sndsel above. He is right on with his response. The only thing that I would add is that transformers usually are designed to work at a certain frequency (such as 50hz) and if you reduce the frequency (to lower than 50hz), then the hystersis losses caused by the lower frequency will result in overheating of the transformer. If you go to a higher frequency, then there should be no problem. It will probably work, but check with the manufacturer.

Question for albertporter and sndsel - two out-of-phase 120 V lines added together should give 240 V. If their phases are 120 degree apart it doesn't add to 220 V. Am I miss something here, or my high school trigonometry gets too rusty ?

Correction to my above post, please replace "out-of-phase" with "in-phase".

Anfield, no your math is not wrong, the confusion comes from two different types of electrical in the USA. Many areas, including my own home are three phase. There is Delta three phase, where two legs are 120 to 138 degrees apart, and two phase, where they are 180 degrees apart.

The two phase is typically 120 volts per leg, making 240 volt, not 220 volt. Delta three phase is 208 volt and if our friend using German amps were to hook up to this configuration, it could actually start a fire.

My intention was to make potential users aware that their electrical should be approved by the manufacturer first and then checked to see if service provided is what is approved for that product.

At my home the three phase Delta is used to more efficiently power my large air conditioner for the long hot Texas summers.

I also use 220 for my power amps, but for that use, the feed is the same as for our clothes dryer. 240 volt which is derived from 120 phase one and 120 phase two with ground.

Thanks albertporter, it is all clear now.