Harry Bloomfield wrote:

That is because the centre tap of the 110v side is earthed to the 240v
earth :-)

The idea is that there should be a maximum voltage to earth of 55v,
which is half of the 110v voltage of the secondary winding.


Thanks for the replies - that gives me a better understanding of the
workings.

I meant to reply earlier but have been unable to see the replies until
now - my fault with my setup.

Regards

David