Earth rod on an T N S

[AA410]

Hi all i have been working on a TNS supply that has a poor reading EDF tell me to put down an earth rod my concern is Ze +R1+R2 can any tell me what is a good reading to aim for when installing an earth rod the best reading i have got is 2.96 ohms is this about as good as it gets hope you can help

 

[Guest123]

An Ra of 2.96??? or was this a Zs reading.

Below 100ohms is a good Ra.

 

[AA410]

The reading of 2.96 ohms Ze was from the earth rod tested with a loop impeadance tester

Hi all can anyone help me with this prpblem the reading is 2.96 ohms from the earth rod gained with a loop impeadance tester but my concern is the R1+R2 on my final circuits say a radial curcuit supplying 3 double socket outlets with a Zs of 0.28 ohms on a 20 amp mcb type B with a maxermum loop impeadance of 1.84 ohms

 

[Sintra]

The reading of 2.96 ohms Ze was from the earth rod tested with a loop impeadance tester

Hi all can anyone help me with this prpblem the reading is 2.96 ohms from the earth rod gained with a loop impeadance tester but my concern is the R1+R2 on my final circuits say a radial curcuit supplying 3 double socket outlets with a Zs of 0.28 ohms on a 20 amp mcb type B with a maxermum loop impeadance of 1.84 ohms[/QUOT

Have you got RCD protection on the circuits concerned? If so then a high Zs is ok.

 

[AA410]

Thanks for your reply i have a 30 ma RCD on this instalation but under fault condition say a live and neutral fault the Ze + Ri+R2 is well above the max thats in the regs ? or have i got it all rong

 

[flukey]

what is the tns reading

if you can get it that low on a spike then i would be well happy with that

 

[Sintra]

Thanks for your reply i have a 30 ma RCD on this instalation but under fault condition say a live and neutral fault the Ze + Ri+R2 is well above the max thats in the regs ? or have i got it all rong

On a live neutral fault your overcurrent device will still operate regardless of Ze.

 

[AA410]

Thanks lads for your help i dont think i can better help than that its the thing with this game you study as much as you can read all the books and work hard to get the result and it still it has a way to take you down an other parth thank again.

 

[steveyce]

EDF are NOT responsable for the earthing arangement NEDL/YEDL or whoever covers your area, EDF are only responsable for the meter and supplying of electric not the cable coming into the property, If it is a TN-CS (PME) contact YEDL/NEDL etc and tell them you Ze is high, they treat this as an emergency and will come out to site within 2 hours and rectify the fault, then you can re-test.

 

[iansparks]

Agree, Report High reading to REC, they will come and sort

 

[AA410]

So who covers the south east ares EDF want 256.00 pounds to make it in to a PME who is respnsable for the incoming supply to a building befor the meter

 

[spadxiii1918]

According to the regs, if a reading above 0.85 ohms for a TNS system (Ze) cannot be achieved, the installation must be treated as a TT system.

 

[mrloy99]

So who covers the south east ares EDF want 256.00 pounds to make it in to a PME who is respnsable for the incoming supply to a building befor the meter

I have to agree with other posters,and just make it TT. Its not such a big issue these days anyway as
nearly everything is on an rcd anyway now.Just means you should leave out the link to the sheath and install your earth spike. You are relying on your rcd for your disconnection times to be met.,and in the appropriate collumn of your paperwork insert n/a. For your earth electrode reading if I recall correctly anything over 200 ohms is considered unstable so what you are getting is very good.
There might also have to be a few other considerations to make as regards TT installations for example a metal consumer unit may not be acceptable unlesss you have a "main" rcd switch before the consumer unit; and isolation on a TT system has to be all pole(2 or 4 as the case may be)
Also maybe worth noteing is reg 542.2.5
the use,as an earth electrode,of the lead sheath or other material covering of a cable shall be subject to ALL of the following:
(1) Adequate precautions to prevent excessive deterioration by corrosion.
(2) The sheath or covering shall be in effective contact with earth.
(3) The consent of the owner of the cable shall be obtained.
(4) Arrangements shall exist for the owner of the electrical installation to be warned of any proposed change to the cable which might affect its suitability as an earth electrode.

 

[ChristianG]

Rec???

 

[Guest123]

Rec???

Regional Electricity Company.