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Discuss Neutral to earth reversal in the Commercial Electrical Advice area at ElectriciansForums.net

C

compaq

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Hi
We had an unusual fault the other day, i thought the members might be able to explain it, here go's.
We got called to an industrial unit to do a job, the supply was TT, TPN, 100A and the protection device was an old four pole voltage operated earth leakage circuit breaker, earth electrode was in place and correctly connected to earth terminal of VOELCB, frame terminal was correctly connected to the installation earth.
The DB was a metalclad MEM Exel 4 way HRC fuse board.
We told the customer that we would have to replace the VOELCB with a RCD before we could carry out the works, he agreed.
We tested the Ze at the DB, it was 0.51 ohms, then got suspicious as we would expect the Ze to be around 20 ohms, knowing the area well.
We had previously arranged to shut the supply off at dinner time, so we had to get on with the job and replaced the VOELCB with a 100mA 4 pole RCD.
The RCD tripped off immediatlely.
We started testing and found a neutral to earth dead short.
Pulled all the neutrals out of the neutral bar one by one and tested them to earth, all tested OK.
Scratched our heads a bit more.
Pulled all the neutrals out of the neutral bar and found the neutral bar was directly connect to earth, then it became obvious, the 'electrician' who installed the DB connected all the earths to the neutral bar and all the neutrals to the earth bar !!!!
We swapped them around and all was OK.
We retested Ze and it was now 25 ohms - as expected.
The neutral to earth short would account forthe low reading of Ze previously obtained.

This installation must have been like this for years, can anyone tell me the problems associated with letting the neutral return down to earth, it seems to me that they had inadvertently created their own little PME system !
Thanks
 
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U

uksel

  • Thread Starter Thread Starter
  • #2
that is a pretty big and not easy to make mistake wouldn't you say?
 
dont see how they had created there own pme system? as the neutral would go straight back to the star point of the transformer.
wouldnt it?
dont thinkit would course a lot of problems as far of general working of the system, hence its beeen like it for years but certainly a bad idea with the general design and fault issues! a big no no
 
W

wattsup

  • Thread Starter Thread Starter
  • #4
I also don't see the problem, unless rcd's were in place. That's how it is on incommers aint it?
If its big ****, all none rcd owners are in for a whole lot of hassle -;) Oh my the UK is burning, everyone is burnt or electricuted......
 
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