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With the Zs readings you refer to makes me wonder if the CU is reliant on parallel paths to gas and water for the "earth" path. Are you sure that the main earth is connected from the CU to MET to incoming supply??

What was the Ze for the old board? i.e. before you started?
 
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??

Don't suppose you got a Ze and PFC before you whipped the old CU out ?
J
 
Try a loop test on the mcb at the board, it could be the main RCD or main switch causing bizarre loop readings causing bizarre loop readings
 
Just go as far as you have done and put it in lim on schedule of inspections (I think you will be covered anyway due to building fabric and floor covering) and just make good use of the departures section, cover yourself as much as you can.
 
One of my old employers used to change my measured zs's to calculated ones from r1+r2 as his assessor used to query them if they were different and he told him he would prefer it that way!!
 
I would do another Ze too....could be the armoured knocked when brushing up cable clippings from the meter cupboard, loosened it off abit
 
but again how far do i go as obviosly only priced for fuse board one of these things i suppose.

Next fuseboard change estimate you do you, should include a caveat, stating that if you identify issues with the installation, which is very likely, that additional costs are to be expected.
 
No unfortunatly i didnt do test on old board. ring reading for excample were l=0.36 n=0.36 e=0.56 r1 r2=0.93 then zs 6.29
Main earth def connected straight to sheath of cable and connections all tight.
 
never tested between earths i will try this on nxt visit to what do you think may have happened?
 
If there is a fault with a mcb/rcbo or a fault thats fair enough but the Zs is an impedance test so thats why I don't agree with calculated Zs values,you should be measuring the total impedance including any protective devices, and comparing with the disc times after all what if you have nipped up the screw on the insulation instead of the copper ? it would /could give you an iffy reading ?

J
 
Just thinking of parallel paths, water / gas being the main earth......every tt system I have been to has just had messily rod in and some with non at all i get readings of around 6 and that's the earthing coming from the gas & water so that's seaming the most likely to me.

PS I know you are on a tns system but used the tt as a example
 
Is the earth solder joint on to the main cable or has it been clamped with an earth clamp? Seen theses before gone loose?
What did you get with the main earth disconnected and supply off? 0.43ohms? Which seems a good reading and you should have a PFC of around 534.9A?
Did you test between main bonding and the board for a low ohm reading?
 
Thank you for all your help il try and arrange date to go back and will let you all know what i did and found. Also has any one got any advice on what i can write on cert to cover my arse in good wording if you know what i mean? thanks again p
 
Thank you for all your help il try and arrange date to go back and will let you all know what i did and found. Also has any one got any advice on what i can write on cert to cover my arse in good wording if you know what i mean? thanks again p

I wouldn't be issueing a cert without some more investigation.........
 

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