Transformer – shield wiring

[jarek]

I have a transformer with a shield between primary and secondary. What is the correct way to connect the shield?. To the audio ground or earth ground? There is no connection between both grounds in the unit.

[Mr Evil]

Connect it to earth.

[jarek]

Connect it to earth

Due to safety issues or sonic preferences?

[djQUAN]

There is no connection between both grounds in the unit.

I thought there should be a loopbreaker circuit or similar in between.

[Mr Evil]

Originally posted by jarek
Due to safety issues or sonic preferences?

Both. If the shield were connected to circuit ground instead, a fault in the transformer could cause the internal circuitry to float at a high voltage, which could be dangerous. If it's earthed, then a fault should blow a fuse, alerting you to the problem.

Also if the shield is connected to circuit ground but not earth, then noise currents could be coupled into the circuit more easily.

Originally posted by djQUAN
I thought there should be a loopbreaker circuit or similar in between.

There have been many discussions on best earthing practice here before. As long as the case is earthed (if it's metal) and everything else is insulated well from live parts, then you don't have to connect earth to circuit ground, although personally I almost always do, just for piece of mind and to prevent problems making connections to earthed equipment when the power is on.

[jarek]

Thanks Mr Evil