Does anybody know of this new regulation that omits the ZS test.

[sham]

On another forum about an high ZS reading about a fused spur feeding a boiler, someone replied that in the new 18th regs if the RCD breaks the circuit within time under test you do not need to check ZS, just R2 continuity test for CPC continuity would be good enough. You just put N/A on the test form for Zs. He even posted an article from Stroma.
This was a response to a question about the Zs reading with his Instrument was 100 ohms higher than his calculation.
Does anybody know more about this, and is it because of rcds and rcbos causing high reading on live ZS redings ?

 

[sham]

MCBS are for short circuits. There has been cases of Live and Neutral touching and it just trips the MCB and not the RCD. It seems that the regs are saying we can't rely on the zs being low enough to help trip the MCB in time which may cause the cable to be permanently damaged or appliance, but we still have protection of persons and livestock by the use of RCDs. This is my thoughts at the moment.

 

[sham]

MCBS are for short circuits. There has been cases of Live and Neutral touching and it just trips the MCB and not the RCD. It seems that the regs are saying we can't rely on the zs being low enough on an TT system to help trip the MCB in time which may cause the cable to be permanently damaged or appliance, but we still have protection of persons and livestock by the use of RCDs. This is my thoughts at the moment.

 

[davesparks]

Where does it say 7667 ohms?
Looking at table 41.5 for a 30mA rcd it’s max zs is still 1667 ohms.
Also see regulation 411.4.204

I don’t have a book to hand but I’m pretty sure that for a TN system they’ve changed it from 50V to 230V giving 7667ohms.
TT systems have remained at 50V

 

[davesparks]

. There has been cases of Live and Neutral touching and it just trips the MCB and not the RCD. t.

Well yes, RCDs don’t work on L - N faults

 

[Deleted member 26818]

Well yes, RCDs don’t work on L - N faults

I think Sham is saying, that although the MCB won’t trip, there will still be RCD protection if anyone comes into contact with electricity due to the L to N fault.

 

[sham]

I think Sham is saying, that although the MCB won’t trip, there will still be RCD protection if anyone comes into contact with electricity due to the L to N fault.

Thankyou

 

[sham]

I

Well yes, RCDs don’t work on L - N faults

I'm saying that the Regs when it comes to TTs, it that we can't always garantee the disconnection of the mcb circuit on time and that it may damage property but as soon it leaks to livestock or people , it must trip within the time and the continuity of CPC must be sound. And results must be recorded.