RCD's won't test unless N & E leads reversed

[Simon O'Dell]

Now I thought I new about RCD's and Earthing systems but cannot work this out.

Carrying out RCD testing with a tester that I know works on other DB's.

On this particular DB cannot get any RCD's to trip on 1x, 5x etc unless I connect the black and green leads swapped i.e. Black to E and Green to N.

Made me think that the supply to DB had reversal of N & E but cannot be as 2 core MICC from main switchroom, with sheath/metal frame as earth and the 2 conductors as L & N. Earthing arrangements TN-S.

The test button on each RCD does work.

I've tried another tester and the same happens, nothing, with standard lead connections, Red-L, Black-N, Green-E etc, but acceptable readings when N & E reversed.

Admittedly, I have not done any dead tests yet due to awaiting planned shutdown but cannot see that anything could be proved from that (polarity already checked - live testing), maybe continuity but the cable is complete from start to finish and never been altered.

Also there is another DB nearby in the same situation and fed from same DB in the main switchroom, but other DB's in the same building and fed from same main switch room ok when testing RCD's?

Any ideas

 

[ianmacd]

What testers are you using as on mine you do not connect the 'black' lead unless you are performing an auto test and then it connects to Earth with the 'green' lead?

 

[ADS]

I'm with Ian - with mine you just connect 'L' and 'CPC' - no neutral.

You also should be testing RCDs on their own - i.e. not under load.

 

[Megaohm7]

Same with mine , red on line and green on cpc on the load side of rcd with loads disconnected..

 

[Badger]

my rcd tester you plug lead into power point and press test job done :^O

 

[kme]

I use 3 leads on the Fluke for RCD testing.

Possibly a N-E fault on a final cct fed from the load side of the RCD. Have you tried testing it "unloaded"?

What are the global ins. readings for supply & load sides?

 

[SLIPSHOD & SLAPDASH]

Flukes use 3 leads. Have you carried out a Zdb (Ze) test yet. Is there an earth connection on the MICC. Is the polarity reversed, L-N.