TT earthing and supply

[jamie-spark]

It is interesting that the non discrimination is shown as a type S 100mA RCD tripping in 100ms at 60mA, which does seem a very poorly designed RCD since the minimum time delay should be 150ms and the RCD should not trip until 100mA (though it is likely to trip earlier, 60mA seems a bit low)

60ma does seem low. But when ramp feasting 30ma RCDs I find it can range between 17ma-25ma with out going load disconnected.
I have fitted a few of these 100 ma s type RCDs recently with 30 ma further down stream on a farm. I may be going back, pretty soon so I could ramp test it and check tripping time and post the results

 

[Engineer54]

Doesn't really matter whether you fit a 100mA or 300mA S type to be honest on a TT system, as additional back-up for 30mA RCDs downstream. What i will say, is of what must be by now, the many hundreds (if not more) of times we have used 100mA S type RCDs for discrimination purposes for downstream 30mA units, i can't remember ever having problems such as been described in this article!!

I must have a more in-depth read, as i haven't had that must time these past couple of days, and have only had a quick over-view....