help needed! my brains been frazzled!

[coxy84]

installed a new cu for some one yesterday, its a tt system incoming voltage 240v and incoming earth from spike 100ohms, all the circuits tested fine every thing works as it should!

now today i went to the same place to change the other small db that supply's 3 circuits the other end of the building. 1x ring and 2x lighting circuits, this small board is fed from the main db with a 40a type b mcb covered by the 63a 30ma rcd. and a 16mm2 3 core swa.

so i did the board, all circuits tested and are good,and with in coming ze of 78.6ohms.
where iv started to have problems is with the rcd test.

i cant get it to trip at x1 or x5 and it doesnt even trip the rcd on the main db side.

iv tried 3x new rcds thinking that it was a faulty rcd but still nothing and its not my tester as iv tried my other tester and have tested on a known working circuit on the main db.

iv had to leave the power turned off tonight as i wasnt happy about leaving it on knowing that it didnt trip when put under fault conditions.


any on got any ideas?

 

[SirKit Breaker]

You haven't done something daft like taken the RCD test at the wrong side of it, the feed side not the load side. An easy mistake to make, i speak from experience.

Cheers.........Howard

 

[ukpablo]

are their two rcd's in series, ie for discrimination?
is ur tester on ac or dc setting or something, i.e the correct setting............just trying to narrow down problem?

 

[coxy84]

Na i dont think so, i tried taking the readings from a socket on the ring,

 

[coxy84]

are their two rcd's in series, ie for discrimination?
is ur tester on ac or dc setting or something, i.e the correct setting............just trying to narrow down problem?

my tester is on the right setting i belive,

100a main switch-30ma rcd -40a mcb-16mm2 swa-100a main switch-63a 30ma rcd-32a mcb for ring
(main duel rcd db) (cable to 2nd db) (2nd db)

 

[ukpablo]

try the rcd at the CU?
all r1, rn, r2 and R1+R2 ok? on ring cct?

 

[coxy84]

yeh same thing wouldnt trip,
i got text book readings for r1 rn r2 and R1+R2

puzzling!!

 

[mark80]

mate from your post it appears you have 2 RCD's in series. Test the plug top fuse or test with the individual leads in the back of the socket and see if that works.
Not sure if this may affect it, if but have you mixed up the neutrals into the RCD when changing it?? As in the supply neutral into the load side of the RCD? Easily done.

 

[mark80]

Sorry just seen the post above!! forget the second part! Wasnt sure if that would affect it anyway! Try doing an RCD test in your house and if it doesnt work then maybe the tester is faulty if you have it on the right settings.

 

[coxy84]

just tried both my testers on my house! and there working perfectly!

 

[Johno]

its a puzzler, i would say go back and triple check everything even the obvious things ie, on your ze it did say ohms and not Mohms

 

[Deleted member 9648]

my tester is on the right setting i belive,

100a main switch-30ma rcd -40a mcb-16mm2 swa-100a main switch-63a 30ma rcd-32a mcb for ring
(main duel rcd db) (cable to 2nd db) (2nd db)

If you are sure that the system is earthed,and your tester is functioning,and you have eliminated a faulty RCD..(almost impossible given that there are 2 in series and you have changed 3 times)...they WILL trip.
My guess would be that you have not correctly wired the RCD's into the DB's...........the fact that neither are tripping when a test on DB2 should trip both would back that up.

Edit....try testing directly the output side of the RCD in the DB with probes ,which will confirm a functioning RCD

 

[coxy84]

Yes i will check every thing again tommorrow, glad im not on price work!

 

[bennett3291]

have u connected your nuetral from ur 16mm2 swa cable into the the wrong nuetral point on ur main cu.

 

[coxy84]

have u connected your nuetral from ur 16mm2 swa cable into the the wrong nuetral point on ur main cu.

checked that and all's good!