400v through a ring final circuit

[Chrisday1990]

Hey guys, I had a callout the other day, 7 fan coil units where not working, these where supplied via a ring final circuit and once all unplugged the circuit engaged, I latter discovered all fan coil units had a dead link between line and earth under a 250v insulation test. The manager and myself was puzzled as to how all the units became shagged, another guy was on site previous and could not find the latter. My only suggestion would be the guy previously got one end of the ring circuit onto another phase thus putting 400v down to each unit, I. Theory this sound logical. Annoy suggestions guys???

 

[Sintra]

If they had one end of the ring circuit onto another phase as you state. I think there would be a big bang.

 

[telectrix]

measure the L-E on each unit with meter set on continuity range. you may then find that it's not a dead short as indicated on IR test.

 

[Chrisday1990]

If they had one end of the ring circuit onto another phase as you state. I think there would be a big bang.

Thanks for the response, there is evidence on the fuse carriers of a huge pop a some point.

 

[Knobhead]

If their American units I’m not surprised about the N→E link. They crop up now and again on CR4. Have they worked? Because 2Ph over there is 230V not 433V.

 

[Marvo]

Well to destroy 7 fan units simultaneously you've got to do something really special and if the previous guy did the deed and covered his tracks then you'll probably never know what happened unless you waterboard the truth out of him. I take it the fans didn't have any protection on their circuit and no internal thermistors/thermal protectors wired up? What kind of motors are they? Are they standard induction motors or maybe external rotor or even EC motors? All you can do is replace them and recommission the entire system from scratch.