We bought an equipment asking for 220V power supply. What we have now is 208V or 600V. The manufacturer said the machine can not run under 208V definately. Then there is a spare 600-240V transformer available and a guy in my office says it is okay for a 220V machine run under that transformer. Can anybody tell me why? for me, 240 minus 5% is 228V,still larger than 220V.
thanks for any input in advance.

I would be very surprised if the equipment would not operate fine on 208 or 240.

That said if you want to get closer I suggest using an inexpensive buck/boost transformer.

You should be able to boost the 208 very close to 220.

I assume this equipment is imported?

Will it run on 60 Hz?

I have personally burned up european 220v equipment trying to run it on 208, both motors and control relays. Even flew this specialist from Germany to tell me so. (Turns very red.) I fixed it with three single phase transformers to boost the voltage. Just remember when sizing the transformers that you don't need to calculate for the entire draw when sizing, just the difference.

Even if the equipment will operate successfully on 208V, when a manufacturer specs 220V, it's in your own best interest to give them what they ask for, if only for warranty's sake. It saves a World of negotiating when some part on their machine breaks, if only because they can't claim the old "Electrician Supplied the Wrong Voltage" line.

16/32 volt transformers can be used in a boost arrangement to get about 222 Volts. You can almost hear the manufacturer's smile when verifying with them if that's OK over the phone.

All too commonly, guys will use 12/24 volt transformers and boost the voltage up to about 239 from 208, thinking they've hit the "target". The target is 220.

Take away their excuse!

^^
I did that once.

Thanks a lot guys for your input.

To iwire, yes, it is imported and it is good for running under 60Hz.

Low voltage is critical for motors which require the correct voltage for starting.

As V²/R is also directly related to torque from the motor.

If voltage is 15 - 20 volts too low, the motor may stall, or growl at 1/7 of the speed, and will quickly burn out.

I take it that your equipment has motors in it.

My experience has been different.

I worked at a place where we had German machinery rated 220 volts and we operated it without issue at 208 and likely even lower.

We also beat the heck out of these motors, at least 10 or 12 very hard starts every hour. No issues with burnt motors or controls.

Now that said I suspect the difference may be in the age, the equipment I was working with was all from the early 1970s, perhaps they used to build equipment a bit more robust back then.

It certainly did not have anything 'electronic' on it, all basic motor starters and mechanical timing relays.

I do agree with electures comment about providing the correct voltage if you want to keep your warranty.