adding rcd to board wont test

[urchy107]

just done my first private job which included a new lighting circuit, new radial, and extending a ring, in a workshop/ car port. the board had been installed new 6 months ago and had no rcd on any circuits so i put an rcd covering all circuits. do i now have to re test every circuit for the certificate or can i just do the ones i altered or added? also i had problems doing an rcd test which turned out to be a 100 ma rcd on a circuit which was powering a stable which is fed from a 40a type b breaker at the workshop board. the 100 ma was faulty so i just connected straight through as its covered by the 30ma i just installed. after this the rcd test was ok untill all circuits were on then the auto test would not run through, but each circuit would test out fine individually, i have a 40,32,32,16,6,6a breakers on one 63a rcd but theres not much load on any circuits? any advice is appreciated, thanks matt

 

[mechelec]

Do you think the RCD upfront may have been a bad idea. Did all the circuits need to be RCD protected?? when you say the "auto test would not run through" what did you mean ? would it trip or not trip

 

[SPARTYKUS]

RCBOs......

 

[urchy107]

not sure, why do you think? theres 2 ring mains, 1 radial, so all skts. a 10mm t&e to a box then conected to an armored cable feeding a stable, and the lighting which doesnt need to be but i thought why not put them on if the circuits test ok. my tester has an auto test which runs through 8 tests, its a metrel combi. it basically wont run through the whole cycle with all circuits turned on but if you switch some off it will, but its not a problem with any specific circuit, do you think i should take the lighting off the rcd, the 10mm t&e to stable has skts so doesnt that need to be on an rcd?

 

[SPARTYKUS]

not sure, why do you think? theres 2 ring mains, 1 radial, so all skts. a 10mm t&e to a box then conected to an armored cable feeding a stable, and the lighting which doesnt need to be but i thought why not put them on if the circuits test ok. my tester has an auto test which runs through 8 tests, its a metrel combi. it basically wont run through the whole cycle with all circuits turned on but if you switch some off it will, but its not a problem with any specific circuit, do you think i should take the lighting off the rcd, the 10mm t&e to stable has skts so doesnt that need to be on an rcd?

urchy107 its really hard to tell without seeing it / more specific information.

I'm sure the problem may very well be with a specific circuit ... ?

Have you done any dead tests? Checked for electrical separation, IR on each circuit. You'll be amazed what you can find. recently dismantled a sub main SWA that was working, 20 Metre run buried 2 inches under a lawn with the mother of all botched joins in the middle (full of chewing gum , no R391 left I guess). IR was 230,000 Ohms between each conductor (or thereabouts). But it worked.

 

[urchy107]

yep done all that, each circuit tests fine on its own but as soon you put them all on together it doesnt.

 

[Des 56]

Why are you testing the circuits individually with the rcd tester
If you have verified its working correctly at source,then circuit loads or faults could give you incorrect information
The Rcd tests are the correct function, or not, of the Rcd

 

[urchy107]

ok, im aware that you only need to test the rcd once on one circuit but i was thinking that if it wont test properly with all circuits on then it may not function properly in normal conditions if there was a fault?

 

[Des 56]

The test is best done at source with no circuits interfering with it

 

[urchy107]

ok so i have no problem then. sweet! but i have never had to isolate circuits before to do the auto test and the way i looked at it was that in the real world all cicuits will be on, have you had to do this before to get a reading then?

 

[Des 56]

The range of tests carried out for an installation will each serve to verify if its within stated limits for each type of test
An insulation resistance test can have a false result if there are items in circuit to affect the test
A test for Ze can be affected if there are parallel paths
An Rcd test can give false readings if there are loads or low neutral/ earth insulation readings

Each test supplements the others and the result is the combination of all tests carried out as per guidances,rcd tests at the source will show whether its ok or no
Rcd tests using a circuit will or could be affected by the circuit itself