Weird Rcd Issue

[Superspark23]

I've noticed on a couple of ocassions now.

That my Type s 100ma rcd will somtimes trip before either of my 30ma rcd. CAN some one tell me why this may happen?

 

[telectrix]

over sensitive?

 

[IQ Electrical]

over sensitive?

If it's a 'front end' device then it could be seeing a much higher cumulative earth leakage value than a 30mA device further downstream.

 

[Superspark23]

most 30ma rcd's will trip at 27ma I cant check this as i dont have and ramp test function on my tester. so presumming 30+30 = 60 why would the 100ma trip first?

I Hope that makes sense?

 

[TIGGERTOM13]

Could be sensitive but a 100 mA RCD would not offer discrimination over the 30 mA. The fault current may be higher than 100 mATo offer rcd discrinination a time delay rcd before the 30 mA one is a better option.

 

[i=p/u]

as above s type, but you mayaswell just put 30mA before cu, and take away 100mA

 

[Engineer54]

If as you stated it's a S type 100mA device, then i'm going with Tel's suggestion, in that the device is probably over sensitive.


Have you subjected the device to any testing as yet??

 

[Des 56]

my Type s 100ma rcd
It seems the op does indeed already have a time delay rcd



I believe IQ has given what I consider the most likely cause of the question asked

 

[i=p/u]

if this happening there must be fault , so ---- a coin normally but s time should delay slightly so must be duff rcd.... as all above between them

 

[TIGGERTOM13]

Didnt see it was a type s sorry, prop over sensitive

 

[Superspark23]

The type s rcd is quite old to be fair, the 2 30ma rcd's are only approx 6 months old. Whats the easiest way of testing for over sensitive rcd's with out doing a ramp test? I dont have accesss to one as the work testers dont have that option

 

[Des 56]

Are any of the circuits (or tails) fed from the 100m/amp s type only

 

[Superspark23]

no, its 100ma type s rcd feeding an daul 30ma rcd board on a tt system

 

[MarkieSparkie]

Is the tripping associated with particular events, operations or at specific times? Does the 100mA, S type, RCD supply any final circuits directly? How far is the nearest property from yours? How far is the supply transformer from you? Please measure Ra, PEFC, PSCC and S type RCD trip time(s) and post the results.