In article ,
david lang wrote:
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?

The 110v is derived from an isolating transformer which removes any
reference to earth that the 240v supply has. In other words you could
safely touch either output line as neither has a reference to earth. But
of course touch both, and you'd get 110 volts which is still a dangerous
voltage. If you then connect the centre tap of the output winding to
earth, you'll get a maximum of 55 volts from either line to earth which is
safe for most, but still of course 110 across the lines.

IMHO, this dates back to when most on site tools had metal casings which
had to be earthed. Using modern double insulated tools would suggest to me
the 110 would be best left 'floating'

Does this only apply to universal (brush) motors?

No - any electric motor etc can be made for 110v. The only difference is
it will take double the current a 240v one would, and need heavier cable.

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?

The CTE makes no difference - the supply is still 110 volts.

--
*Can fat people go skinny-dipping?

Dave Plowman London SW
To e-mail, change noise into sound.