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.

 

[snowhead]

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

The person installing the 4 pole probably didn't think it through and probably hasn't seen the results of doing it,, untill now.

 

[havo one]

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??

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.

hope it's ok to sidetrack a little, we are fitting 4pole contactors on boards at present so staff can have an easy mode of switching off at end of shift. There are lots of gaming machines connected to the circuits most of which have inbuilt computers (I believe) do you think I should connect neutral direct. Thanks

 

[snowhead]

do you think I should connect neutral direct.

Yes without a doubt.
Who decided on the 4 poles?

 

[Nigel]

Thoughts on what?

 

[havo one]

Yes without a doubt.
Who decided on the 4 poles?

tbh i ordered the contactors myself without considering the implications of the neutral switching. ill connect neutrals direct tomorrow.
thanks.