[brijar]

If it is a 220V American oven, then you will need to provide two 120V sources that are out of phase (180 degrees) with each other to simulate how it would be powered in America. Simply using two 220V to 120V transformers connected to the same source would not work since the outputs would be in phase (and the microwave would only ever see 120V at a time). Without knowing the internal wiring of the microwave, I'm not sure how you could hook it up to the single phase 220V.

As far as the ground and neutrals go, from my understanding, the neutral wires are connected to ground at the breaker box. I believe this is only to allow the use of GFCI's. Ground Fault Circuit Interrupters measure the current on the hot wire and the current on the neutral wire and will open the circuit if those currents are not within about 20mA of each other. This happens if the current from the hot happens to flow through the ground wire instead of neutral. If you get in between the hot and the ground, the GFCI will see that not all the current is flowing back through the neutral wire and will trip, hopefully preventing you from getting badly electrocuted. I'm not sure if your office is fitted with GFCI breakers (located in the breaker box instead of right behind the wall plug), but if it is and you connect the microwave's neutral to the ground, the GFCI part would not be able to function properly if electrical current finds a path through ground instead of neutral. The breaker would still trip if there is a really high current. But it would be better to connect the microwave ground to the ground from the wall. What you do with the neutral depends on how the microwave is wired as well, I think. You may have to leave it disconnected and then use both the hot wires from the microwave with the hot and neutral from the wall to get the proper 220V into the microwave, if it just has a large center tapped transformer inside.

Not sure about the effect of using a 60Hz device with 50Hz power, but Google seems to think it is usually not good. Best to call the manufacturer of the microwave and ask them, I think.

Good luck!