Earthing responsibility

Brightsparkiow · Mar 20, 2022

Hi all,
Holiday village, brick built lodges circa 1960s. Supply is 35mm 4 core armoured, each phase and n comes in to Henley blocks and out to next unit, armour in/out terminated onto metal plate that also has a connection for earth to local consumer unit in each bungalow/cabin. 1 phase used in each unit into a sub meter (unit owner pays the site owner for electric used) then up to CU. No access to where the supply comes from.
So I am calling it TNS… views?
The Ze is 1.08 ohms ZeDB is 1.04 (previously Ze 0.51 on 2017 eicr) ... I notify the owner, but not DNO as surely it is a sub main, so site owners responsibility?
am I missing something?? Surely should be less than 0.8 ohms and the change is of concern anyway… what would you do? thanks all.

westward10 · Mar 20, 2022

You cannot quote an earthing system unless you can access the source nor can you give a value of Ze.

timhoward · Mar 20, 2022

I've been confused by this arrangement myself before.
The cable coming into the property/properties is best thought of as a distribution circuit, the earth conductor being a CPC.
You can't know where you stand with Zs until you know the protective device used upstream. For example, that value is within the 5s distribution circuit time of a 32 amp BS88 fuse.
Assuming a TN system, there's certainly not a lot of 'headroom' left for final circuits rated at B32 or above, so I'd agree this needs checking out carefully.

pc1966 · Mar 21, 2022

It is suspicious that the measured Ze is much higher now.

If it were still at 0.51 ohm then it is fine for 5s on a 60A supply fuse. At over an ohm it is not leaving much margin if disconnection on OCPD is needed and if the various houses have older installations that might well be the case.

Any idea how long this sub-main is? Are all of the Ze values suspiciously high suggesting some issue at the supply end, rather than some joint point between buildings?