Thank you all for your answers and added comments. This forum is helping me lots in advancing my knowlegde as an electrician. I have A question about a lose neutral causing voltage spikes. What theory do you base your conclusion?
A multiwire branch circuit in a 3 phase system would be 2 phases and a neutral with loads connected phase to neutral. So if you lost the neutral, then you would have a series circuit with phase to phase Voltage source, at least up to the panel where the circuit originated.