R1+R2 on 2 core Hi Tuff

Where does the TT island start - is the feed between the buildings also TT, or is that part of the PME ?

(and if it is PME, does it have an earth with it - is there metal conduit or similar - if not how does the fuse blow if a garden fork finds it ? This may not be the safest choice of cable.)


There are two things to verify -

1) will the wiring before the RCD be protected by the MCB or fuse upstream ? - this is normal sums for you I think.


2) Will the wiring after the RCD be protected by it?

Here the load side CPC stops at the electrode, so you could wander lead from there to inside the garage to verify the earth path from a socket front or whatever, or short CPC and L at a socket and measure R1+ R2  from the external electrode to the live at the start of the garage circuit. (only with it off, of course...)

Then you need to verify the electrode separately.


Far better if it is already up and running do a Zs check instead, and see if that would fire the RCD, which I imagine is 30mA. That not only checks the wiring is present to the electrode but also that the electrode is actually in the earth, and not cut off short, or corroded or inside a buried  plastic flower pot or something silly. expect 100 ohms or so for the electrode, and 3/5 of SFA for the R1 + R2 so Zs is really the electrode reading as the R1+R2 is lost in the flicker of the last digit.

Mike.

Where does the TT island start - is the feed between the buildings also TT, or is that part of the PME ?

(and if it is PME, does it have an earth with it - is there metal conduit or similar - if not how does the fuse blow if a garden fork finds it ? This may not be the safest choice of cable.)


There are two things to verify -

1) will the wiring before the RCD be protected by the MCB or fuse upstream ? - this is normal sums for you I think.


2) Will the wiring after the RCD be protected by it?

Here the load side CPC stops at the electrode, so you could wander lead from there to inside the garage to verify the earth path from a socket front or whatever, or short CPC and L at a socket and measure R1+ R2  from the external electrode to the live at the start of the garage circuit. (only with it off, of course...)

Then you need to verify the electrode separately.


Far better if it is already up and running do a Zs check instead, and see if that would fire the RCD, which I imagine is 30mA. That not only checks the wiring is present to the electrode but also that the electrode is actually in the earth, and not cut off short, or corroded or inside a buried  plastic flower pot or something silly. expect 100 ohms or so for the electrode, and 3/5 of SFA for the R1 + R2 so Zs is really the electrode reading as the R1+R2 is lost in the flicker of the last digit.

Mike.