Hi, It's nice to get this kind of questions!

Mostly the surge test voltage to a product-under-test(put) is related to
the operating voltage, or the out put voltage of the put.
It means if the operating(using) voltage of the put is higher, the test
voltage comes to higher.

The following formula shows the calculation of surge test voltage, and
this is recommended by ICWA(International Coil Winding Association),
but this formula came from a long experience of the users, as they say,
" The Rule of Thumb ", not from a strict theory.



Es = (2 Eo + 1000) * 1.4

when Es = Surge test voltage
Eo = Operating(Using) voltage of the put

According to this formula, the surge test voltage is only depended on
the using voltage of the put, even if the wattage or the size of the put
is extrimely larger.

Hhhhh.... It may sound you it's rather strange if a put's a motor, and it's
Horse Power is bigger than 1500, that means the size of that motor's
diameter is larger than 100 cm, and is the surge test voltage of this put
is the same as with the smaller one, if the operating voltage is same?

Yes....it's true, and there's no strange or problem at all...
Let's think of it more deeply.....if the HP is bigger....it means the
turns of the winding is less...and maybe the diameter of the wire is thicker..
Then the test voltage of each turn comes up higher autometically...
So there the test condition is more strict...and that's all... O.K....

Thank you so much for your question.
If there's another question you have, don't hesitate to ask anytime...

Have good times! bye...