I have three zones which are constantly blowing halogen (12v and 240v) and 240v light bulbs. No idea of the problem – I just keep replacing bulbs!. But I have a new problem which is blowing 12v transformers.  

On the loom, power goes to a 12 v transformer which feeds 3 halogen bulbs. This works fine. The same wire then goes off to another transformer which in turn feeds three more halogens. Somewhere in the same switch the power feeds 2 x 100w light bulbs.  

In the past few weeks I have gone through 3 transformers connected to the same three halogens. (it’s one of these transformers that runs three halogens off it)  

First transformer blew. I had the choice of 2 live and two neutrals – I probably made the wrong choice. So I understand that fail.  

Next transformer I just replaced, turned the lights on and it blew.  

Next transformer I checked the bulbs. On one I found the wiring tail had melted the insulation and the two bare wires were now touching. So I replaced the tail. Before wiring the transformer I wired in a 240 light fitting and turned the power on. Everyting worked just fine.   So I took the light fitting off and wired in the transformer. From there I wired in the first halogen. Turned the lights on and everything worked. Wired in the second halogen, lights on all worked. Wired in the third halogen, turned on and all worked.  

Blow me down, half an hour later the three lights had stopped working and sure enough the transformer has blown again.  

So I have pulled the lights out and here is a photo of a tail. It’s melted and presumably shorted the wires again.  

I’ve run a volt meter over the wires and its 243v   Any ideas where the problem might lie.