step down transformer power usage

We're looking at adding a step down transformer going from 440 to 208 and then to another power panel so we can have both voltages available. My question is I have always been under the impression a transformer consumes a certain amount of power even if you are not pulling power from the transformer. Would we be better off just having smaller individual transformers to meet each machines requirements since some machines may be idle.

The answer

While the transfomer WILL exhibit a slight amount of eddy current 'loss' due to basic physics of the transformer design, the open secondary circuit (the low-voltage side) will not be 'pulling' any current from the transfomer core's magnetic field, hence, the amount of unloaded 'waste' power will be essentially non-existant.

The way for you to measure the 'waste' is to hook up the primary, and measure the amount of heat being eminated by the transformer when not connected to the load.

That really depends.

It will probably be cheaper to have one big transformer. As long as it's not just sitting idle for long periods of time with no load on the 208 side, it won't waste much. The bigger the transformer the more waste current, BUT as secondary load goes up, the waste current goes down slightly. Waste current will be fairly low, and if you're looking to run multiple machines from one transformer, the power savings probably won't equal the the cost of the complex wiring and multiple small transformers. The other thing is each machine's transformer would have to be switched off at the PRIMARY side to keep them from wasting power. If you're only looking to run a couple machines occasionally on the 208v power, you MIGHT save power by putting transformers on each machine and shutting them off on the PRIMARY side when not in use.