Sub board in garage

[DD1990]

ok so im working in a property and the lady has a 16A RCBO on the RCD side of the fuse board in her house... it feeds a 100A 5way rcd CCU in her garage supplied by 2.5 SWA... everything in the garage turns on fine but when you plug anything into a socket it bypasses the 100A RCD in the garage and the RCBO in the house but trips the RCD in the house... if you take the RCBO neutral out and put it on the non RCD side of the house fuse board everthing works fine but you get a loop reading of 1.31ohms....overly confusing any help would be great.

 

[ExArmy]

i would put the sub main into an MCB on the non RCD side of the board.
whats wrong with 1.31ohms anyway? what is it connected the other way

 

[Octopus]

Shoulds like a N_E fault in the garage. Time to get your MFT out and do some investigation, like IR

 

[D Skelton]

N-E fault in garage. Whoever decided to put three RCDs in series though is an absolute moron! When you've sorted out the fault in the garage, connect the submain to an MCB on the non RCD side of the main DB, and make sure the MCB is connected to the busbar correctly, I suspect your higher Zdb is because the RCBOs clamp had missed the busbar.

 

[GLENNSPARK]

i would put the sub main into an MCB on the non RCD side of the board.
whats wrong with 1.31ohms anyway? what is it connected the other way

would you?
and where in #1 did the O/P mention earthing arrangements?

 

[Geoffsd]

if you take the RCBO neutral out and put it on the non RCD side of the house fuse board everything works fine

Doesn't that suggest that it was wired incorrectly before and the RCBO is not on the RCCB side?

 

[ExArmy]

would you?
and where in #1 did the O/P mention earthing arrangements?

what are you getting at?

 

[GLENNSPARK]

what are you getting at?

and if the install was TT then you would be using a 100mA RCD for the armoured at least top end....
or 30mA top end for the sub & finals in the garage...

 

[ipf]

what are you getting at?

Not enough info, what's the reason for the 100mA RCD ?