How to Calculate kVA Rating of Control Transformer

Find out the VA ratings of all devices that will be powered from the control transformer (PLC, computer, accessories; solenoids, relays; motor starter coils and other contactor coils; etc.) Add them all up and then multiply by a service/safety factor of 1.25 (or whatever the local code may dictate).

Dear,

It is true that totalling the KVA ratings of all control devices may not be the same as total KVA load on the transformer. Since, it is the vectorial sum of KVA ( not a scalar quantity ) Infact, you need a smaller size of X'mer by about 0.83 times the total sum of all KVA

But, it is equally true that if you total the KVA of all devices, then, derating & safety factor is also considered in it, you may go very safely with the total sum of KVA to select the Control Transformer size.

Sorry but have I got this right?
Your designing a PLC controlled MCC panel and yet have to ask the most basic question of total strangers on an internet site?

Pure fantasy!

If the contactor coils are also supplied by the control transformer, the sizing is a more complex exercise due to high inrush VA. To get some idea of what is involved, please download and study this document : http://samplecode.rockwellautomation.com/idc/groups/literature/documents/wp/1497-wp001_-en-p.pdf

You must be knowing voltage requirement and frequency for the circuit. Inrush current you have to findout for selecting the KVA rating.

Maybe I'm overstating the obvious, but if you have 415/230V available, why would you need a control power transformer to get 230V control power? Why not just tap off of one phase with a fuse and connect the other side of your control circuits to Neutral?