earth fault on a chiller

[Davey1988]

The thing is. If there was a big fault with the transformer. Using the earth as a "refrence" could lead to a earth fault with maybe 230 flowing down. Less than likely but always a chance.

Since its tripping the rcd there's oviously something wrong and I don't think it should detect this as the transformer should be isolated 230 from 24v.
Any ideas lads??

 

[davesparks]

The thing is. If there was a big fault with the transformer. Using the earth as a "refrence" could lead to a earth fault with maybe 230 flowing down. Less than likely but always a chance.

Since its tripping the rcd there's oviously something wrong and I don't think it should detect this as the transformer should be isolated 230 from 24v.
Any ideas lads??

Can you describe this 'big fault' in detail please, maybe draw a diagram to explain?
And voltage doesn't flow, current flows

 

[Lucien Nunes]

The transformer should indeed isolate the 24V circuit from the supply under normal working conditions, but you seem to have missed the point of why the secondary is earth referenced. Suppose for example the wiring harness becomes damaged and one leg of the 24V circuit comes into contact with the 230V line. In this case, it causes leakage to earth from the 230V via that link and trips the RCD or MCB. If the link were missing and the 24V circuit just floated, the fault might not stop the machine working but the 24V circuit would be elevated to 230V from earth and hence dangerous.

 

[UKMeterman]

To add to the above some estop switches are deliberately designed with one side earthed, so that if an earth fault occurs then the fuse blows and cuts out the machine. IF the transformer is suspect then remove all connections, link all the primary teminals together and seperatly link all secondary connections, apply your megger on the 500V setting between the primary and secondary and test continousy for 1 minute and report back with the result.

 

[Davey1988]

How is it possible to read neutral to earth on the opposite side that it's liked to on a transformer 230 to 24v. I thought they supposed to be separate Circuits.

anyone shed any light on this. Does this sound like a tx problem or can you get the reading?

 

[Lucien Nunes]

I still don't know why you are interested in the 24V circuit. If you are getting faulty insulation readings from the 230V supply terminals, the problem appears to be with the 230V circuit. You mentioned that closing a contactor manually resulted in a low reading. What was the reading, what does the contactor control, have you tested the controlled load downstream of the contactor? E.g., if it's a motor line contactor, the motor windings.