RCDs and high loop impedance

[solaker]

Hello everyone
I was wondering if it was possible in a TNCS system to add an RCD to a final circuit with a loop impedance exceeding the values stated in tables 41.2 - 41.3 to ensure fast enough disconnection during an earth fault. I had thought it was but if so why are RCBOs subject to the same max Zs as MCBs in table 41.3. After all RCDs are used in TT systems because of the high Zs arent they? and an RCBO is just an MCB and an RCD combined. Can someone point out what Ive misunderstood please
Many thanks
(sorry if this question seeems a bit retarted)

 

[Mr Mark Sparks]

i think what you have asked is a question in the 2391 and they wanted 3 ways to get over eli above max 1 was upgrade cpc 1 was downrate mcb and 1 was fit rcbo/rcd hope this helps