Earthing Reading

[paul_sut]

Hi all i did a fuse board change the other day and when testing i got a ZE reading of 0.43 and a KA of 5.93 why would the KA be so high, also zs failed on all circuits for breakers. This is TNS. what would any one recommend??

 

[Octopus]

Are you sure your KA is correct?

 

[Rauer]

Try your tester again!

 

[paul_sut]

i've just got one of these new megger mft1710 and i pressume i have i think it came up 593A? also why would my zs fail for example for the ring 32a breaker i got 6.29??

 

[Octopus]

i've just got one of these new megger mft1710 and i pressume i have i think it came up 593A? also why would my zs fail for example for the ring 32a breaker i got 6.29??

In red - are you sure? Your OP said 5.93Ka - which is it?

Your ring may have a problem, what were your "dead" tests like? Or is it all circuits?

 

[paul_sut]

on all circuits

 

[p11jor]

Loose connection somewhere in the original install? I had a zS of 4000 once!

There is a few fixes tho, you could add some bonding to create parallel paths, this may bring your zs down

You could rewire it with a bigger CSA cable to lower the r1+r2 value

Or as you will now have rcd protection you can have a maximum of 1667ohms but if it's over 200ohms check it out!

 

[p11jor]

Just another thought if you were taking the Ze then the main earth would of been removed from the earth terminal, once that was replaced to start doing zs's could the terminal screw cross threaded and backed off abit?

 

[paul_sut]

All rcd protected now but is old house all decorated etc dont want disturbance if you know what i mean. main bonding all done to water and gas 10.0mm, main earth 16.0mm to sheath. Another reading i got was the boiler which was new circuit tight connections etc and the zs was 6.41 on 16a breaker.?

 

[Octopus]

Hum, not sure what's going on here. Silly question but you did reconnect the earth to the CU/Met didn't you?

 

[paul_sut]

yea i thought this aswell checked all connections all ok and tight

 

[p11jor]

Mmmmm wierd one, has the whole wiring been inspected?? I.e is the ring final results ok? It could be a case of a DIY job few jbs spuring of the 2.5 in 1mm Somthing on the lines of that?

 

[Rauer]

Check the main earth connection , then get onto the supplier, least that's what I'd do!

 

[Rauer]

How were the r1+r2's?

 

[Rauer]

Hasnt that ze failed too tho? Daily certain a tns is 0.18

 

[telectrix]

try measuring Zs at the outgoing of MCB. if its higher than the Ze, then it's the MCB and/or main switch affecting the value.

 

[telectrix]

Hasnt that ze failed too tho? Daily certain a tns is 0.18

TN-S max. Ze is 0.8.

 

[paul_sut]

Thanks for all your help i think im gonna arrange a re visit as this baffled me, yea all r1 r2 and end to end good on ring all good. but again how far do i go as obviosly only priced for fuse board one of these things i suppose.

 

[jumpin jax]

Ze for tns is max 0.8, have you checked your loop readings on your meter with your known monthly check source to check meter ok

 

[paul_sut]

ZE max is 0.8.