help with rcd problem

[Mr Mark Sparks]

evening all,
went to look at a mates cu the other day tt system 30ma rcd main switch tripping out randomly
earth loop to stake 150 ohms.
earth loop with everything connected 1.30 ohms.
before i did any insulation tests i did a full set of rcd tests and it wouldnt trip via my tester (mft1552) however test button did work,

so said i would change cu as replacement main switch for old cu not available,
replaced cu today with wylex dual rcd cu tested circuits as i put them back.

now the odd thing there is one lighting circuit that tests >299 l-n >299 l-e >100 n-e when i connect this it stops the rcd from tripping on test.
swapped rcds round and tried circuit on both side of cu but with this circuit connected rcd will not trip, with it removed it will.

what sort of issue can stop the rcd from tripping

for those who dont know me i am 22yrs time served with 2391



at the mo the circuit is just via mcb not on either rcd
and i am waiting to here if random tripping has stopped

thanks mark

 

[Plonker 3]

Could you not put the circuit you "think2 is causing the problem on a RCBO, especially as it is a TT system?

 

[Guest55]

The OSG does advise testing as near as practicable to it's point of installation, and load supplied should be disconnected, but struggling to find that in the BGB
J

It should be in GN3 , gives more detail on the nuts and bolts of testing.

 

[Mr Mark Sparks]

Could you not put the circuit you "think2 is causing the problem on a RCBO, especially as it is a TT system?

yep going to put one in tomorrow to see if it will trip under test or nuisance trip.

 

[Plonker 3]

Either way, I would leave it in once fitted.

 

[sparks1973]

11.1 osg p 106...so yes..i was wrong Biff on the testing too close thing...although some devices (MEMs) dont like it...

 

[Nath88]

I remember going to a job a collegue had been to..... Rcd main switch not tripping so he ordered a new one and i went to fit it on his day off.
When i went to test it, wouldnt trip either so i did my tests and found a low resistance fault between Neutral and earth which turned out to be a trapped neutral in the fused spur. So sorted that and then checked both rcds and both were fine.
Just an idea

 

[sparks1973]

Could you not put the circuit you "think2 is causing the problem on a RCBO, especially as it is a TT system?

that may just mask the problem...not solve it as who says the RCBO will function?..

 

[Jimmy Boy]

11.1 osg p 106...so yes..i was wrong Biff on the testing too close thing...although some devices (MEMs) dont like it...

Thats the one !
J

 

[Plonker 3]

that may just mask the problem...not solve it as who says the RCBO will function?..

Maybe but at least the circuit would then comply with the regs in regards too TT systems.

 

[sparks1973]

Maybe but at least the circuit would then comply with the regs in regards too TT systems.

but if the RCBO doesnt want to let go....well then it wont comply will it..

 

[sparks1973]

the point i`mmaking is masking the problem or just brushing it under the carpet..whatever..isn`t the way is it Dillb

 

[Jimmy Boy]

Well he will have to test the circuit at a point close to the board, it's connected by the flying N and the functional E so be interesting to see.
J

 

[Plonker 3]

the point i`mmaking is masking the problem or just brushing it under the carpet..whatever..isn`t the way is it Dillb

So leaving the circuit unsafe is a better option is it? At least the RCD is present and can be tested and certified as such.

 

[Mr Mark Sparks]

things like today make me want to go all cicruits on rcbos
if only people wanted to pay the extra!!

 

[Jimmy Boy]

things like today make me want to go all cicruits on rcbos
if only people wanted to pay the extra!!

Well I was wondering what the next 18th might ask for.............. !
Think about it ! LOL
J