help needed! my brains been frazzled!

coxy84 · Jan 20, 2011

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?

coxy84 · Jan 20, 2011

wirepuller said:
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

i will do in the morning! cheers

ukpablo · Jan 20, 2011

Already been said!...........did not see second page

coxy84 · Jan 20, 2011

whats the minimum efli before the rcd wont work? 1667 springs to mind?

SimpleSimon · Jan 20, 2011

Is it not tripping at all or not in the specified times?

coxy84 · Jan 20, 2011

not at all

Benny_Boy · Jan 20, 2011

Johno said:
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

That's what I was thinking Johno

Des 56 · Jan 20, 2011

Do a high current loop impedance test on a load at the remote dist board

Benny_Boy · Jan 20, 2011

stick your tester on 500mA and try it @ 5xI delta N

If it won't trip then maybe it's back to triple check the wiring.

Deleted member 9648 · Jan 20, 2011

Benny_Boy said:
stick your tester on 500mA and try it @ 5xI delta N

If it won't trip then maybe it's back to triple check the wiring.

Cant see it...the meter has been confirmed ok...the RCD's have pretty much been confirmed ok by virtue of being changed several times....if they are correctly installed they must trip @1x never mind 500ma....I still think they are not installed in the DB correctly.
Do make sure we get the outcome Coxy84....an intriging problem.

Benny_Boy · Jan 20, 2011

Des 56 said:
Do a high current loop impedance test on a load at the remote dist board

Good idea Des.

If your Ze is 100 Ohms, your tester is OK, and the RCD isn't faulty, it really only leaves the wiring?

Surely......

I think I'm going bonkers now

Benny_Boy · Jan 20, 2011

Have you energized it yet?

coxy84 · Jan 20, 2011

wirepuller said:
Cant see it...the meter has been confirmed ok...the RCD's have pretty much been confirmed ok by virtue of being changed several times....if they are correctly installed they must trip @1x never mind 500ma....I still think they are not installed in the DB correctly.
Do make sure we get the outcome Coxy84....an intriging problem.

i will go over every thing in the morn! ill be sure to let you know what the out come is!

coxy84 · Jan 20, 2011

Benny_Boy said:
Have you energized it yet?

cheers for your help, yeh energized it after the dead test were preformed, iv left it turned off and locked of for tonight though

dan jones · Jan 20, 2011

where is the second db fed from an mcb in the first board if so try and dissconnect the second db from the installation then try the first rcd or maybe if the earth path isnt good enough maybe its not putting enough mA down through the rcd if you get me also you could try and put you tester on 100mA at 5x and see if it trips then