I have a 3 phase 208 volt 11kw oven. What size breaker should I use.
Is it 208/11000 which would be 50 amp
Or 240/11000 which is 45 amp.
Current power source is 208 volts and currently has # 6 wire

If in the USA, the breaker and feeder needs to be rated 25% higher than the load.

11000 watts / (208 * 1.73) = 30.5 Amp load * 1.25 = 38.125 amp circuit rating.

A 3 pole 40 amp breaker using the existing #6 wire will work fine.