Now this is why you should have your wiring tested on a regular basis the problem is a house is considered safe because your lights go on and off

IGM for your infomation
A RCD should not trip at half fault current 15mA
At 30 maA the RCD should trip in less than 0.2 seconds but I have tested hundreds of Rcds and most trip at less than 0.025 of a second.
On a ramp test as a rule a RCD trips at 20 – 23 milli amps

As for where does all these safe values come from, well alas it was not descovered by guess work or animal testing but it was done on real people back in the 1940's in various camps in eastern europe during the holocaust. Not nice to know eh

saladdodger – I don't disagree with your points, in terms of tripping time I'm more used to IDMT or plain over current responses, I woiuldn't know the exact timings on an RCD, however for your information an RCD or for that matter any circuit breaker, will not limit the fault current only the length of time it lasts. Even 0.025 is over one cycle and the prospective peak current will have been reached (twice on a symmetrical break, once on an asymmetrical break, which is what actually happens). If you want to limit the fault current you need a fault current limiter, of which we are currently installing the first one on our system and it is superconductor based and needs to be rather cold to work. Earlier ones used air bag explosive charges. A fuse can in some situations act as a primitive fault current limiter, but not a circuit breaker can not. Trust me.

just checked back and can't believe this is still running!!
How many posts is troutie's thread??

igm

consider yourself trusted

Sorry – I re-read my reply and its a bit over the top. Particularly at the start. And I certainly didn't know that a 30mA RCD starts to go at two thirds of that. An IDMT (and IIRC a fuse) does not go at setting – it will only go at a value over setting, and that was what I was refering to.

I think my "don't buy a house from and electrical engineer who thinks he's an electrician" statement stands though – probably more so in retrospect.

Bet the original poster has either given up and gone home or shot himself by now…