quick question

[switch10]

just a quick question guys, currently waiting for my niceic assessment on wedsnesday and my 2 jobs i have submitted are. 1 consumer unit replacement , with rcbos on tt install. 2. consumer unit replacement and 1 x additional socket.

1. tt job, i have done consumer unit and completed all testing, however the r1, r2, rn and R1+R2 readings seem a bit high, let me explain.
test on a 32amp ring main
r1 0.56 ohms
r2 1.33 ohms
rn 0.60 ohms

R1+R2 = 0.75 ohms

if i state this is certificate will this be ok? as surely im not responsible for work i havent carried out? what form would i need to state the defects on? thanks in advance

 

[bugsy]

Where do you consider there is a defect and what actions do you think are required

 

[robsparky1975]

Did you zero your leads before testing,all readings would appear that the area covered would be quite large,but both R1 0.56 and RN 0.60 would appear correct(within .05 ohms of eachother),you would expect R2 to be 1.67 greater than R1 so about 1.00 ohms in general terms(all in guidance note 3) slightly higher reading may indicate poor connection/rusty earth on metal backbox etc/test leads playing up,and R1 & R2 to be 1/4 of the sum of R1&R2 added together so R1 0.56+ R2 1.00 = 1.56 /4 =0.39(as a general rule in gn3) so to me would roughly be expected,although sitting at my pc,with no knowledge of your install about the best i can do,if the zs is less than 1667 ohms for tt supply niceic will be happy(although Ra will need to be less than 100 ohms or he will not like it),so if Ra is say 80 ohms and r1 & r2 .75 you are well within limits for a tt,you have tested the circuit and proved continuity,when you change a ccu and have tested all the circuits on it,all you are saying on your cert is that you have upgraded the ccu to a newer set of regulations and that the existing wiring and accessories are safe to put back into service,make sure all the earthing and bonding is 100%,niceic man will see straight away that you know your stuff and you will sail through,good luck.

 

[switch10]

Did you zero your leads before testing,all readings would appear that the area covered would be quite large,but both R1 0.56 and RN 0.60 would appear correct(within .05 ohms of eachother),you would expect R2 to be 1.67 greater than R1 so about 1.00 ohms in general terms(all in guidance note 3) slightly higher reading may indicate poor connection/rusty earth on metal backbox etc/test leads playing up,and R1 & R2 to be 1/4 of the sum of R1&R2 added together so R1 0.56+ R2 1.00 = 1.56 /4 =0.39(as a general rule in gn3) so to me would roughly be expected,although sitting at my pc,with no knowledge of your install about the best i can do,if the zs is less than 1667 ohms for tt supply niceic will be happy(although Ra will need to be less than 100 ohms or he will not like it),so if Ra is say 80 ohms and r1 & r2 .75 you are well within limits for a tt,you have tested the circuit and proved continuity,when you change a ccu and have tested all the circuits on it,all you are saying on your cert is that you have upgraded the ccu to a newer set of regulations and that the existing wiring and accessories are safe to put back into service,make sure all the earthing and bonding is 100%,niceic man will see straight away that you know your stuff and you will sail through,good luck.

cheers for the reply.

yes i did zero the leads before testing, will double check results today and check all connections to try bring the r2 result down a bit , which will then hopefully give me a lower R1+R2 reading closer to the calculation . Ra was infact 85 ohms so even with the results i have im with in the limit.

just