Massive damage. Neutral fault

[Michael White]

I work for an FM company, we’ve just taken on a brand new refitted and rewired premises.

There is a 3phase DB supplying sockets into which there were loads of electronic equipment which has suffered multiple failures. The DB is supplied via 4pole contactor which is switching the Neutral. It’s a TNCS supply and I’m thinking this contactor switched Neutral is the problem. The contactor has now been replace with a 3 pole and solid link to Neutral.

Thoughts??

 

[westward10]

What is the purpose of the contactor.

 

[Dillb]

What makes you think switching the neutral is causing the faults?

 

[Michael White]

The contactor is for BMS control for energy management.

I should have mentioned the contactor went faulty yesterday and one of the poles was open circuit and perhaps a slack coil supply as it was dropping in and out a couple of days ago.

 

[westward10]

A lost neutral is almost certain to cause component damage.

 

[Pete999]

If the equipment is getting damaged due to switching off the supply under fault conditions withe the supply, then I would have though the client should consider UPs backup to allow for a controlled shut down of the electronic equipment, a costly initial outlay, but a money saver in the long run, imo

 

[snowhead]

Unless the contactor N pole was late break early make, breaking the Neutral certainly would have caused problems.

Unless it's a perfectly balanced load across all 3 phases, which it won't have been with single phase loads, the phase voltages can rise (and fall) momentarilly at the time of switching.

 

[Michael White]

I’m thinking just the action of switching the contactor may have meant that not all 4 poles closed at the exact spilt second and might have cause massive overvoltage in the phases. Or the neutral was open circuit for a time leading to anywhere up to 415v applied in the phases.

I wouldn’t say I’m an expert on this but this is my understanding of it.

 

[Michael White]

My last post was written just as you were posting this. It most certainly wasn’t any form of late break early make. Just a bog standard 4 pole contactor.

 

[Lucien Nunes]

Sounds a likely cause to me, especially if the contactor has been chattering in and out and maybe going randomly high-resistance in the neutral pole. I've seen more electronics cooked by neutral loss on a TP+N supply than pretty much anything else. Not sure why anyone would think of switching it on a BMS contactor, seeing as you don't even need to switch it on an isolator.

 

[westward10]

I agree it is an odd thing for a bms to control.

 

[Wilko]

Just trying to understand why they would've wanted to switch the neutral in this way?

 

[Ian Mills]

in france alot of house have a 3 phase supply and all have the neutral switched and I have never seen a problem but last year in a storm the neutral cable going to a house got broken and there was a lot of damage to electrical equipment in the house, fridge dishwasher, pool pump, a electric air freshiner melted and nearly burn down the house would check all neutral conections and then recheck them,

 

[Michael White]

The building is fully BMS operated. There is a valid reason, for which I can’t fully divulge as the electrical contractor may well be part of this community and I would assume there is a large finger pointing exercise about to commence.

We’ve checked the drawings and it should have only been 3 pole. Seems the install contractor took it on themselves to switch the N via 4 pole.

 

[westward10]

BMS systems do not control dist boards for general lighting and power.