Hello, i understand the basics of how transformers work but have not come accross them much until i started a new job recently. These may seem like stupid questions but i would appreciate it if you experts could clear up a few things- As both coils are isolated is it normal to have the output voltage present between the output and input Neutral or Earth if the output 0v is not grounded. i.e i had a 240v to 24v tranny (output zero not grounded) and upon testing i had the correct voltage out between 24v and 0v but i also had 24v between the 24v and the input Neutral or ground. Is this right ? i thought i would only get i voltage between 24v and the output 0v or have i not grasped something? the tranny was working o.k. Will an RCD on the input side protect against an earth fault on the output side? This might sound the most stupid but i cant quite understand where the 0v current flows to on the output side, i.e on the input i know current comes from the live wire through the coil and out through the Neutral where it is dissipated th ground at source. But on the output it flows out of the 24v through the load and back to the 0v, but then where? how can it flow round the coil as i thought current only flowed from a greater to a smaller potential?