Insulation resistance on a transformer

[Norv]

Is it possible to damage a transformer by doing an insulation test without disconnecting it first. It is one of those large-ish wire wound transformers used on a 12v Wire Track Lighting System, because this is what I did & the cb trips when I turn the light on. Its on a two way light switch. Not sure if it worked before cause its a new installation. Was going to do all the other tests tomorrow but curiosity got the better of me & I wanted to see it working before I left....

 

[RF Lighting]

Did you zap it with a full 500V live to neutral?


What is the VA rating of the trannie?

Is the MCB a 6A type B

 

[Norv]

err........ yeah

dont know I'll look tomorrow.

yep.

It doesnt trip everytime, its a bit intermittant.

 

[RF Lighting]

Big wire wound trannies have a habit of tripping 6A type B MCBs when they are switched on from cold.

If the Zs for the circuit is low enough I'd be tempted to try fitting a 6A type C MCB and see if that cures it.

 

[Norv]

ok thanks.

 

[partpdoctor]

hi
the tranny will probably be ok....
test l-e and n-e as normal
when doing the l-n test open the local switch...

the mcb tripping is the inrush on start up (until the magnetism builds up to oppose the current , the supply "sees" the tranny as a "short")
you need to fit a c type mcb. dont forget to check the maximum Zs as it will now be half of a b type for the same current rating....
hope this helps you