isolation transformer question

[corporalspiffy]

this is the isolation transformer i have.



can someone give me an explanation of its purpose and design.
will this float the secondary circuit or will it just reduce noise from the mains supply?
there is no continuity between the secondary ground and the primary ground.
i plugged in an appliance to it and measured full mains voltage between its chassis and a wall receptacle which seems to indicate that it was not isolated.

if i disconnect the ground on the secondary side will the whole secondary circuit then be isolated?

why is there is secondary ground if it isn't grounded to the mains ground and why did i measure full mains voltage on the appliance chassis and the mains outlet receptacle.



thanks



secondary side


primary side

[IanB]

The purpose is to isolate the secondary side and reduce the risk of electric shocks caused by faults in the devices plugged into it. Since the secondary side is floating there should be no potential difference available between the secondary side and earth ground to cause electric shocks.

The secondary ground may possibly be connected to a center tap on the secondary side, putting it at a potential of 60 V relative to both output conductors. This would enable a fuse to blow under fault conditions and also reduce the shock risk in the event of a person touching an active conductor and the grounded chassis at the same time. (I am not certain of this without seeing more details of the transformer.)

When you measured "full mains voltage" to a mains socket, how did you measure? Did you measure between hot on the mains side and the metal chassis? When you did this measurement, did you use a "low Z" setting on the meter? It is possible you measured a phantom voltage caused by capacitance in the system.

[retrolefty]

My understanding for using the isolation properties of such a transformer is it allows one to 'remove' the neutral to ground connection that most AC household outlets have, this connection being made at the service panel feeding the outlet. With the isolation transformer the user is allowed to remove any reference to ground for either secondary output pin of it's output outlet. There should always be a hardwired connection between 3rd ground pin from input to output as it's a safety/fault current carrier, but the user is free to have ground pin and either one but only one of the AC output pins to ground at the load end or left 'floating' from house ground.