high ZS and not tripping out RCD problem

[ElAl]

I have just finished a job on a house that has not been altered electrically for 40 years, my job was to rewire kitchen, upgrade earthing to current spec and fit new distribution board to 17th edition.

All well and good but when I tested it, the old existing ring was giving me high resistance readings and not tripping out the RCd at all.

I have backed off the sockets and tightened and checked all connections, and the earth of the ring seems to be continous (end to end by meter).

How do I correct this to ensure Rcd trips and loop impedence is down?

regards
El Al

 

[telectrix]

have you measured r1,r2,rN? on the old ring final ?what readings? does the rcd trip off your new circuit ( kitchen). ? really need more info. Ze for starters.

 

[ElAl]

Sorry Ze is fine, all other circuits test normall and good, particularly my new kitchen radial. There is a break on ring in r1 the rn is 0.88 r2 is 1.88. It is just on the house socket circuit! My polarity checker shows an earth fault but my end to end shows earth continuity!

help!

 

[telectrix]

ok, so r1 is o/c. start with that. J/Bs, sockets behind things. dis 1 leg and work round ring till you lose the L on a socket. you' may be lucky and find the cpc fault in the same place. as your RCD is not tripping, assume you've tried it from a particular socket, it's cleasr that the signal from your tester is not getting through from that socketg, try another socket. it's just a question of elimination, sweat and head scratching. let us know how you get on.

 

[ElAl]

Thank you for your prompt reply !

My intention was to find the r1 break as you suggested, but i do not understand the earth problem, my tester just shows over 2000 ohm on the furthest socket on loop test and no result on rcd test , and my polarity checker shows an earth fault. I decided to run a separate 4mm earth to the first socket on the ring (just as a test) and then went to the furthest socket and i got readings on the rcd test, but too slow. This led me to think if i was to connect a 4mm earth to closest socket and a 4mm earth to furthest socket I may be able to reinstate earth integrity by the back door so to speak . If I cannot find a fault on the ring is this an acceptable and feasable option?

 

[telectrix]

you could split the ring into 2 radials, assuming you've got a spare way in the CU, and put each on a 16A or 20A MCB.

 

[tony mc]

As telectrix has said its a step by step process to locate the faults.

Split the ring at a socket outlet (midway if poss )and at the CU. Join the line and cpc of one of the tails at the CU and start checking your sockets to see if you get a reading. If no reading at all then there must be a break prior to the first socket outlet or in a JB. (Thats checking for a reading at line & cpc at each socket)

Try the otherside of tails at the board and again try to obtain a reading at a socket outlet to locate what side of the ring that tail is feeding.

It pays to also write down the sockets you do get readings from and which set of tails at the cu you have joined so you don't get mixed up.

Its a process of elimination but xray vision would be a benifit to see whats concealed away.

I take it your polarity checker is a plug with lights on.
Remove that socket when it says no earth but do the correct r1 r2 tests at all socket outlets to obtain your readings don't rely on a socket tester they are just a quick guide.

 

[BlueToBits]

As a last resort, particularly if I suspect the fault is in a hidden JB, or more tha one break in the ring , I find this sometimes helps:
Draw a sketch of the house and the socket positions
Split the ring at the CU
Link N-E on one leg of the ring - the other open circuit
Test N-E at each outlet
By noting the results you can then draw in the cables that link the sockets to determine the order.
Disconnect the link and link L-E
Repeat the test for L-E going around the ring in the correct order - you should get similar results as before
If the test shows open circuit you then know in which cable there is a break.
It's usually possible to cut a lot of this process out in practice
By systematically drawing it out, it can sometimes reveal something obvious that was missed.