transformer queries

[davelerave]

to calculate the contact rating for switching the primary of say a 10kva 400v(2-phase trafo)

do i calculate the FLA-ie: 25amps and use ac-3 rated contacts (or do i need ac-6a)

and are there any particular precautons to be taken regarding 'voltage spike's when switching trafos

 

[controlman]

Found out what the inrush current is. Plot this on the curve of the graph of the contactor bearing in mind the electrical life
eg. switching operations per day
The inrush could be as large as 15x = 375amp