14amps going down main earth connection

[plugsandsparks]

Hi guys, have posted in tell us your faults a potential issue i have with high earth currents, detail is in other post, appreciate any help - thx
post 827

 

[netblindpaul]

Can't find your other post?

 

[plugsandsparks]

have cut and paste - hopefully mods will be gentle

Guys need some advice / ideas...
Background:- I have installed a new TP board off a 200A breaker from the MDB. I was doing some load checks so i could advise the client how much capacity is remaining for new machines and i though i would clamp test the earth to see if there was any activity, when i saw a couple of amps i got a bit distressed so went back to the MDB and clamped the main earth connection from MET to MDB and was reading 14amps - uck a duck i thought whats going on here, anyway with the help of my brother we did some tests in a short time when the factory was quiet.
1. Incoming supply 400A neutral off armourings
2. Incoming supply has separate about 16sqmm earth cable disappearing down into the entry point, not visible outside so not sure if it goes to an earth rod or back to substation.
3. Readings from MET to MDB 14 amps
4. Readings from incoming earth cable was just 1.7mA
5. 10 DBS in total - isolated 9 with no impact on readings.
6. Last DB 12 way was running office computers so did not isolate it but switch off non essential breakers leaving 4 lighting breakers and 2 socket breakers.
7. Switched all all lighting and current dropped dramatically to around 2 amps.
8. Double checked line and neutral loads to this DB and they did show a roughtly 14A difference.
9. Removed the earth connection from MDB to MET but no lights went out and no voltage was present between MET and earth tail from MDB
10. No DBs appear to be cross bonded

At this point i ran out of time and had to put all everything back together but i was left with a couple of thoughts
1. The factory lighting consists of 35-40 6ft double fluorescents of the old switched start type - parasitic loss ????
2. Some of the lights are wired incorrectly neutral to earth but still manage to find a circuit off the strutural steel work when i disconnected the earth that was carrying the current.

Appreciate any thoughts guys, i had to work fast to get the tests done in the time available and have probably missed something perhaps obvious..

 

[Knobhead]

1/ neutral off armouring?

Please tell me you’re not serious.

Or are you describing a bodged up TN-C-S system?

Look at the neutral connections to the source of the supply.

 

[Engineer54]

Maybe he has a 3 phase concentric cable Which has confused him?? Can't see how you could use the armouring as the neutral, not unless the SWA cable hasn't been glanded, ...If that's the case a whole can of worms is about to be revealed!! ...lol!!! Not least the CSA of the SWA!! ...Here We Go!! ...lol!!!

 

[plugsandsparks]

sorry concentric neutral - was confused...