Mike wrote:

Hi guys, it's been a long time since I have posted to RCM, I mostly lurk.
I come begging for some of the group's wisdom.

I have a friend who has purchased an old Mori Seiki SL-3B Lathe with
Fanuc 5T control for his high school shop. Since it was made in Japan
many years ago it did not come with UL or CSA approvals, something that
is required before it can be hooked up in the school. (BC Canada BTW) The
normal procedure for imported machinery is to get an approval sticker
from the local electrical inspector.
He has done a preliminary inspection and stated that he requires an
insulation test of 2x the supply voltage plus 1000v for one minute,
during which time he checks for insulation breakdown and listens for
arcing. I assume he will be using a megger. We're a little reluctant to
allow 1400 volts to be applied to the input, parts for this age machine
aren't easy to come by. He said boards may be removed during the
testing, but that still leaves the DC spindle drive and servo power
supplies. I do not know if the rectifiers can handle that much voltage.

Is this a reasonable method of testing what basically amounts to a
computer? Is it going to kill some part of the machine?

This is a standard, easy to pass test called
a Hipot Test. The current is limited during
the test so the chance of damage is small.

The voltage is applied between ground and the
neutral/hot conductors. The diodes should
not see it as an overvoltage as they are either
on the secondary of the line transformer, or
not connected to ground.

If the unit has built-in surge protectors or
varistors connected directly to the AC input,
these should be removed before the test and
then reinstalled. If they are left in, they
will conduct (as they should) and cause the
unit to fail the test.

Hipot tests are done to most computer power
supplies.