You need scrambled brains to sort this!

[johnboy6083]

is this a TNC system?

 

[ian.settle1]

No neutral 400v across single phase equipment

 

[johnboy6083]

thats kinda the route im thinking, the lost neutral situation, neutral currents returning via the metalwork. Does this system incorporate phase failure relays that would shunt trip the ACB on voltage imbalance?
where are the neutral-earth bonds for the star point of the tx? if any

 

[Knobhead]

I should have banned you Lenny. In effect it's our old friend a shared neutral.

Here's the drawing I had to do to work it out.

View attachment 14750

 

[Knobhead]

The guy still wouldn’t accept it.
It’s not very often you get a Indian university professor loosing his rag, but he convinced the guy I was right.

 

[Knobhead]

Thanks to all that had a go.

 

[Richard Burns]

Well done Lenny, I couldn't even work out why there were breakers in the earth or whether there was a neutral connected at all!
Thanks for the diagram Tony one massive amount clearer than the "description"

 

[johnboy6083]

Keep em coming Tony. I like this type of thread. It's better than the my light doesn't work, can you tell me how to do my job?

 

[Knobhead]

Keep em coming Tony. I like this type of thread. It's better than the my light doesn't work, can you tell me how to do my job?

I'll have to introduce you to Coolyer, one of our serial giberish posters. He doesn't react to being insulted!

 

[Engineer54]

Tony's diagram shows exactly why you should never have 3 pole ACB's and solid neutral on dual feed switchboards!!! This problem would never have occurred if all the ACB's were 4 pole.... Same situation occurs when you have a stand-by generator included in the switchboard arrangement, using 3 pole ACB's (breakers). The stray neutral currents fly all over the system unbalancing and tripping out any earth fault relay protection incorporated on the system....

 

[mogga]

the diagrame makes it 100%understandable but im glad i stick to 400v stuff n leave the higher stuff for those who know what they are talking about

 

[Knobhead]

It’s not just ACB’s as E54 pointed out, but many switches have a removable neutral links. It’s all to easy to overlook refitting them after testing.
In the drawing the most important link that should have left in was the one between the two transformer sections.

 

[Engineer54]

It’s not just ACB’s as E54 pointed out, but many switches have a removable neutral links. It’s all to easy to overlook refitting them after testing.
In the drawing the most important link that should have left in was the one between the two transformer sections.

If the ACB's were all 4 pole, then the only removable links on the system would be the two N-E links between the N and E bus bars. (Earth bar not shown on the drawing)

But if the system installed is as in the drawing, then yes the links will be everywhere on a 3 pole breaker + solid Neutral system...

 

[Engineer54]

the diagrame makes it 100%understandable but im glad i stick to 400v stuff n leave the higher stuff for those who know what they are talking about

Err, ....this ''IS'' all 400 Volt stuff!!! Only untill you get to the other side of the TX's will you be in MV territory!! ...lol!!!

 

[Knobhead]

I suppose the beauty of the systems I’ve worked on is you would never come across earth fault protection until well away from the main boards. All the transformers had REF obviously. The main neutral at the transformer switchboards were always kept continuous, links were removed for dead testing only.
RCD’s were as rare as hen’s teeth. About the only place you would find them would be in the few sockets used by the conveyor belt vulcanises, these had to have pilot/earth monitoring as well.
It was a shock to the system when the portable tool rules were relaxed to allow 110V, previously it was 50V centre tapped. Portable welding plant was unheard of, it had to be fixed or diesel.
Just before I came out of my time I was working in the contracts management office, I had fun! Can we use…… NO! What about….. NO! Suppose we can’t use the bloody kettle can we? NO, plenty of fixed mashing urns about the site, you use them. I was only applying the rules, but I made a meal of it.
The first computers on site caused chaos. We found a way around that eventually by getting the M&Q inspector to issue dispensation for offices. Then came the plant control rooms, it got messy. The 20[SUP]th[/SUP] century caught up with us in the end. Things changed from trying to find ways round the rules to applying them.

PS the earth bars are on the drawing.