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Welchyboy1

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Hi all

on a TT system, upfront 100mA s type rcd at origin then 5 submains out to 5 small CUs each with its own 30ma rcd main switch

on testing 30mA rcds they are totally fine with upfront RCD bypassed but when tested with upfront RCD installed, all 5 rcd trip early on test

Im thinking this is something to do with the S type RCD test button earth connection maybe?

but why is this effecting the testing of the downstream devices?

all cabling is fine, all high readings

and i have loaded the circuits with as much as i can 10-15A and the rcds are all holding fine, also the Stype is new and testing out fine too

is this an issue thats going to cause potential problems?

Many thanks
 
Hi all

on a TT system, upfront 100mA s type rcd at origin then 5 submains out to 5 small CUs each with its own 30ma rcd main switch

on testing 30mA rcds they are totally fine with upfront RCD bypassed but when tested with upfront RCD installed, all 5 rcd trip early on test

Im thinking this is something to do with the S type RCD test button earth connection maybe?

but why is this effecting the testing of the downstream devices?

all cabling is fine, all high readings

and i have loaded the circuits with as much as i can 10-15A and the rcds are all holding fine, also the Stype is new and testing out fine too

is this an issue thats going to cause potential problems?

Many thanks

Can you explain where you are testing and what happens please !
 
I am testing the 30ma rcds at the actual rcd itself and by local socket outlet next to each of the 5 cu's

the rcds are all tripping at 1/2 x test

i tested them all before installing s type and they were all fine

all rcds including s type are new

also the s type is four pole with two phases running through it and neutral, L1 and L2

L3 is empty(is this an issue?)(the test link is wired through L1 on this rcd)

one phase supplies 2x submains to cu's
second phase supplies 3x submains to cu's

all via switchfuses
 
I am wondering if there is anything else that has been connected in the intervening time?
When you are testing the 30mA RCDs at the board is the rest of the board disconnected or are there other circuits still connected, if there were a fault on one of those circuits (or just a small amount of leakage) then this may be pushing the RCDs over the limit.
If you link out the 100mA RCD and have it switched off does the same <15mA trip fault occur? I know you say with the 100mA bypassed they are fine, but then you say they were tested without the RCD in place.
 
Hands up I'm an absolute numpty, it was at the end of a long hard day

Had another look this morning and first thing I noticed I still had my test meter on 100mA

Well spotted tony

****!!
 
I was interested in this setup - is the S type RCD for fault protection, or additional protection, or both? Additional protection may be required if a submain is e.g. in a partition < 50mm from the surface. But then you should use a 30mA RCD but you can't because you need discrimination. i.e. I am interested if you have hit the apparent conflict between needing an S type 100mA RCD for discrimination and needing a normal 30 mA RCD for additional protection.
 
I was interested in this setup - is the S type RCD for fault protection, or additional protection, or both? Additional protection may be required if a submain is e.g. in a partition < 50mm from the surface. But then you should use a 30mA RCD but you can't because you need discrimination. i.e. I am interested if you have hit the apparent conflict between needing an S type 100mA RCD for discrimination and needing a normal 30 mA RCD for additional protection.


It was a set up for feeder pillars on an events field, they hold fete's, amusements, boot sales, etc etc
set up was

150m 35mm 4core SWA out from supply at lesuire centre PME earth, 63a tpn switchfuse at scource

then converted to TT system 100mA s rcd covering switch fuses/SWA sub mains out, 30mA rcds covering final circuits at each cu at 5 pillar boxes dotted around field

final circuits were 2x single sockets, 2x commando 16a sockets at each pillar for hook ups

1x 2m 5/8 rod at each pillar

RA- 3.8 ohms :)

s type provides fault protection for submains only, additional protection for all final circuits
 

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