High Ze Value on TNS

DjSparkos · Sep 7, 2009

Hi all,

Could someone please advise me what the standard procedure would be if you were to get a high Ze reading of 8 Ohms. It was a TNS earthing arrangement. Main earth was upgraded to 16mm, gas and water both verified at 10mm. Im figuring that i will have to liase with the electrical supply Co.

Any advice gratefully recieved.

zupos40 · Sep 7, 2009

DjSparkos said:
Hi all,

Could someone please advise me what the standard procedure would be if you were to get a high Ze reading of 8 Ohms. It was a TNS earthing arrangement. Main earth was upgraded to 16mm, gas and water both verified at 10mm. Im figuring that i will have to liase with the electrical supply Co.

Any advice gratefully recieved.

Temporarly you must fit 30mA or RCBO to protect all of the circuit fed from this supply as at present you have not protection against earth fault occuring in this installation.

Do not leave it as it is, sod law something will go wrong, if a fault occurs there a greater rish of fire/ electric shock.

I would contact your local supplier and took to them about up grading the supply from TN-s to TNC-S or converting it to a TT installation.

If you upgraded the CCU still get the earth changed, as present condition could get worse, you may be lucky and find they upgraded the cable in the street and it a simple case of changing the head, had it a few time in London, other wise it could cost hundreds of pounds, then the TT may be the only option.

andyb · Sep 7, 2009

I had this last week whilst doing a PIR, I called the SSE and they had someone round within 2 hours.
They were there untill 8pm digging the garden up. They did not leave untill they had sorted it.
When I went back next day the Ze was .29 ohms.

DjSparkos · Sep 8, 2009

Nice one for the replies

theleshollis · Dec 16, 2009

I had this today, Ze of 15 ohms on the TNS, reducing to 4 ohms with the aid of the water pipe!!!

Luckily I'd already fitted a dual RCD CU at the origin.

Chappie from Eon came out within an hour, admitted that it was probably their dodgy joint in the road, preached the indoctrinated spiel that it wasn't down to them to supply a good earth and said that the customer could apply for a PME or I could sink an earth rod.

Well, I knew THAT. Earth rod it is then.

He "Made a note of it" and switched off the main switch.

No chance of him checking the neighbours' houses to see if they have the same problem. How long would it take a BS3036 fuse to break a 56A earth fault into the washing up bowl? Or would Doris get roasted first??

Les

zupos40 · Dec 18, 2009

theleshollis said:
I had this today, Ze of 15 ohms on the TNS, reducing to 4 ohms with the aid of the water pipe!!!

Luckily I'd already fitted a dual RCD CU at the origin.

Chappie from Eon came out within an hour, admitted that it was probably their dodgy joint in the road, preached the indoctrinated spiel that it wasn't down to them to supply a good earth and said that the customer could apply for a PME or I could sink an earth rod.

Well, I knew THAT. Earth rod it is then.

He "Made a note of it" and switched off the main switch.

No chance of him checking the neighbours' houses to see if they have the same problem. How long would it take a BS3036 fuse to break a 56A earth fault into the washing up bowl? Or would Doris get roasted first??

Les

What is fuse and cable cpc, I am sure cable insulation would be damaged etc as well as increased shock risk, if you had not installed RCD.

theleshollis · Dec 19, 2009

zupos40 said:
What is fuse and cable cpc, I am sure cable insulation would be damaged etc as well as increased shock risk, if you had not installed RCD.

Hi,
That last bit was a ranty hypothesis really, with the water pipe connected, Zs at the board is approx 4 ohms, so the earth fault current would be 57 amps. If it is the same at the neighbour's house, and they only have 3036 fuses for protection, in the event of a fault - What happens next?

I'm going to send a polite letter suggesting the neighbours at least get their Ze tested. There are only about 6 semis in a row in the middle of nowhere. The work I've carried out at my customer's house has made it safe and covered my responsibilities to them, but I'm a worrier.

Les