I'm not sure about IEC standards (the US standard for surge testing is IEE522).
Can you clarify whether you're asking about testing required in purchase order for new motor, or testing required in purchase order for repair/rewind of motor, or periodic test performed for monitoring?
In the NEMA / IEEE world, NEMA MG-1 is used for purchase of new motors.
NEMA MG-1 (2009) section 20.35 address surge withstand and testing requirements.
Users can specify motor to withstand IEEE522 surge test of either 2.0 or 3.5 pu.
There is mention that surge test can occur at various stages of manufacture:
a. On individual coils before installation in slots (65% of full test voltage)
b. On individual coils after installation in slots, prior to connection with stator slot wedging and
endwinding support systems installed (80% of full test voltage)
c. On completely wound and finished stator (100% of full test voltage).
NEMA leaves it to the customer to specify which if any of these stages testing will occur at.
Personally I would recommend at a minimum final test of completely wound stator (condition c). If the motor fails at that point, it is the financial responsibility of the supplier. If you don't test, then you run the risk that undetected weakness in turn insulation won't show up until it sees a surge in service. In fact if you don't test, there is really no teeth to "specifying" 2.0 or 3.5 p.u. surge withstand capability at all.
