"david lang" wrote in message
. ..
Hi
As I understand it, 110v power tools are considered safer because the 110
volt supply is Center Tapped to Earth, so any shock would be 55 volts -
I'm
not sure exactly how this works - could someone explain please? Does this
only apply to universal (brush) motors?

Secondly, I also understand that a power tool with an induction motor (saw
bench, pressure washer) in 110 volt can't be CTE, so any shock would be
110v. Is that right?

Dave

This centre-tap to earth business works when feeding a device from an
isolating transformer. Since the secondary of the transformer is isolated
from earth, unlike one side of the mains supply that feeds it, you can
choose
to reference the secondary to earth from a centre
tap if available. The centre of the transformer secondary is now tied to the
mass
of the earth, so the ends of the secondary only ever rise 55V rms above
earth potential. Imagine a seesaw with the centre pivot being the reference
point:
each side will go up and down, but only half the distance compared with if
you held
one end still and let the free end waggle up and down.

Any shock you are likely to get will be between one end of the secondary
supply
and earth ( since you are permanently connected to earth via your feet ), so
you will
probably only get a 55V rms shock.

I don't believe the sort of motor you are feeding has a bearing on the
application of this
safety method. If someone else knows better I'm sure they'll post.

Andy.