tncs ze 12 ohms?

swift_2 · Aug 8, 2011

Hello people I was wondering if you could help me understand how a tncs ze value be 12 ohms. All breakers off main conductor disconnected and two lead test with megger 1553 between line and earth tester set on high as no trip not needed. Reading is 12 ohms,so to check this again I left earth disconnected at board and took reading with earth probe on the neutral/earth block. The weird thing is all zs readings complied with regs, there is no earth on the water so surely the readings cant just be complying due to the gas equiptional bonding? Any thoughts would be appreciated. Thank u in advance

yellowvanman · Aug 8, 2011

If its what you describe then it doesn't surprise me. If your sure Ze is that high call the DNO and let them know about the Ze.

GLENNSPARK · Aug 8, 2011

I know it sounds daft but have you checked the termination screws are tight in the earth-neutral block? Is it 16mm earthing? I have heard of cable made god nows whare mascerading as copper but infact its alli with a copper coating.........Your Zs may comply due to parallel resistances bringing the true Zs down......

Blowcat · Aug 8, 2011

What was the Ze at the neutral/earth pme connection?

mechelec · Aug 8, 2011

get DNO out to sort it. Ring the emergency number and they will be out in less than 4 hours. You cant leave a job like that can you ??

Smugley · Aug 8, 2011

I've had a Ze much lower than that and called the DNO. They had it fixed before I arrived back there the next morning.

telectrix · Aug 8, 2011

measure your PSSCand PEFC. they should be virtually identical. if not, then you have a fault with the PME.

onions1066 · Aug 8, 2011

i've had this a couple of times before, had a reading of 23 ohm today in a flat, work it back to the mains, this was due to a loose neutral in the DNO's isolator, tighten up and and away i go, if i remember right that is exactly the same fault as before.

swift_2 · Aug 11, 2011

GLENNSPARK, The termination was tight, could be that type of cable !

Blowcat, The Ze at the neutral earth point was 12.0 while croc clip around conductor was 12.1.

Mechelec - It wasnt my job, a friend of mine had asked me to look at the house as he was thinking of buying it, nobody living there.
The scary thing is the owner had had it inspected in 2007 where this had been mentioned in the report I seen the other day. In the schedule of test results all Zs readings were measured high, Im thinking the Inspector used the calcuated method. Apparently the owner was a diy guy and has wired the house himself !
Telectrix, PFC and PSSC were identical 2.4 Ka
Didnt think of the loose connection on DNO side of neutral, that could be the cause.