whats the score with this old MEM board

[oldtimer]

Hi guys as you can see the picture attached is an old MEM board with a 100mA rcd/main switch so can somebody confirm wether this was ok to use at the time installed I suspect 20-25 years ago but then again I know someone will correct me here and also why use 100mA /

 

[telectrix]

seen a few of these installed in the 80's. in fact , it was an exact MEM boards as this one where the RCD bumped the |Zs readings up to 350 ohms.

 

[alarm man]

is it a tt system

 

[oldtimer]

is it a tt system

No TNS I think the unit is mounted on a board so I pulled it back and found all the circuit had their outer sheath (T&E) stripped back 300mm from the back of the board with a 25mm SWA with a earth clamp around the armour hence the guess at TNS. I was called out to this today chasing my tail trying to find a earth neutral fault until I sussed out that all the FCUs were single pole and traced the problem down to a electric fire connected via a SP fused outlet and a SP switch fuse that I took for DP DOOOOOOOOOOOOOOOOOOOOOOOOOO

 

[oldtimer]

Just to add to my mail above this is board is fitted in a flat in central Edinburgh so my main concern is because its around 20 years old was it acceptable then to fit a 100mA RCD (ELCB) ?

 

[Richard Burns]

Looks like a pretty standard arrangement to me, I have seen several of these on various systems.
100mA RCD as protection for all circuits makes it safer than no RCD, but does not prevent it being potentially lethal but the trip time is fast so safe, obviously does not meet current regs but no need to change it.
The wiring at the back is another matter entirely, needs a proper earth and sheathed wiring.

 

[malcolmsanford]

Over the years I have see quite a few TN-S systems with RCD/RCCB or even ELCB protection. Often it would be the DNO fitting an upfront one as their earth had deteriorated, normally it would be because they had replaced or repaired a joint and lost the cable integrity, so they fitted the RCD/RCCB/ELCB for protection.

Often also a TT would have been converted to TN-S/TN-C-S and just left.