Zs still needs to be within specs for 17th
There seems to be a very heavy reliance on RCDs in the 17th
They are not the most flawless of items and need that earth path
Waste of time having one if Frank Spencer changes the light bulb and dead shorts with his fingers
The primary protection is still the main and best protection.
Low enough Zs for the overcurrent device to operate before the killing time is up
Hi Des, but if Frank shorts with his fingers, he has nothing to do with the Zs path
'Overcurrent device' is a misleading term
An overcurrent is simply a current exceeding the rated value, and can occur anywhere in the circuit (not confined to the CPD)
If we are talking about short circuit current, again Zs is irrelevant
If we are talking about earth fault current, again thats what the RCD is there to protect
I know there is a failure rate of RCD's (not laeast because of the emulsifying of the lubrication due to lack of testing by the user), but lets be honest, how many of you have actually tested a 60898 to see if it ACTUALLY trips within the required time for a given fault current?
And back to my (sorry, 'the'
) original point, if the circuit doesnt comply, the action to be taken is supplementary protection (additional protection under the 17th) with an RCD
But if the circuit is on an RCD anyway, the Zs measurement becomes irrelevant
And I think 'assuming' devices are going to fail to operate when required to do so is a dangerous road to go down.
Godd to talk though, nice to see some deep and meaningfull discussions on here, now where's Mr Bane when you need him.....