Ze & Zs-- unacceptable readings

telectrix · Nov 5, 2010

think that the live 6mm is looped from the home which is the main problem as regards earthing. and the 16mm was originally for another purpose long lost in the past. as of today, i have terminated the 16mm into a " garage box" 2 pole isolator, 40A MCB ( for home) 16A MCB (for RCD socket local) and made the live 6mm safe. tomorrow morning will hnopefully not be ******* down and i can trace the other feed.

telectrix · Nov 6, 2010

Right, sunny day, further investigation shows that although the rat,s nest and the home are supplied from the same cut-out, the home is not supplied from the mess in the pic. this morning i have TT'd the home and dissed the armour at the home end. Ze measured at178ohms, within the 200ohm max. the home owner's electrician has been informed by me that he must replace the 100mA RCD with 30mA. He is asking me for a cert. on the work i have done, and i am thinking EIC, limitations to be stated as install TT earthing only. don't think MWC will do. does anyone know if there is a specific cert. for work outside the home?

telectrix · Nov 6, 2010

I know what comes next. the guy is niceic so will say a TT system has to be under 100ohms. brb says 200. already feel like telling him to go forth!

fathom9 · Nov 6, 2010

telectrix said:
I know what comes next. the guy is niceic so will say a TT system has to be under 100ohms. brb says 200. already feel like telling him to go forth!

Why do you want to do that? Sounds like he does his job properly and if everyone did you wouldnt have that mess there.
As far as I am aware my mate whos in the NIC says they work to 200 ohms and has no idea where you got 100 from.
You need to complete and eic and state the change to TT on that particular sub circuit only unless youve changed others. You will need to record the method of measurement, measured resistance ( with rod disconected from met if using method 2) type of electrode and location. 178 is still pretty high though if it was me I would try a longer rod or different position to try and get it down. If its too high there may not be enough prospective current to trip breakers. It sounds like youve got a bit on there sorting that mess out. Have fun!!
OH dont forget your supply characteristics will have to be recorded seperately because I presume that isnt TT.

pushrod · Nov 6, 2010

fathom9 said:
Why do you want to do that? Sounds like he does his job properly and if everyone did you wouldnt have that mess there.
As far as I am aware my mate whos in the NIC says they work to 200 ohms and has no idea where you got 100 from.
You need to complete and eic and state the change to TT on that particular sub circuit only unless youve changed others. You will need to record the method of measurement, measured resistance ( with rod disconected from met if using method 2) type of electrode and location. 178 is still pretty high though if it was me I would try a longer rod or different position to try and get it down. If its too high there may not be enough prospective current to trip breakers. It sounds like youve got a bit on there sorting that mess out. Have fun!!
OH dont forget your supply characteristics will have to be recorded seperately because I presume that isnt TT.

Agree that 178ohms is high, especially for a winter/wet ground reading, but it is a pscc that will take the breakers out in this case and an earth fault of more than 30mA that will interrupt the supply via the rcd and 1667 ohms will still give that.
Oh and welcome to the forums

telectrix · Nov 7, 2010

it.s a nightmare. the supply cable is daisy chained feeding 5 homes,not mapped out properly, at each, armour is jubilee clipped with fly leads.so could be poor connections. going to try and trace it from source, reading ELI and PSCC at each. prefer to get the original earthing up to scratch than rely on TT. as said, at 178, it's a tad high. in response to you, fathom, i,m not knocking the home owner's spark for doing his job right. it's just that myself and the site owner are stuck in the middle, dodging cloudbursts trying to rectify the problem. bearing in mind that we have to interrupt the supply to all 5 homes while working and he's sitting in the warmth writing out condemnation notices.