RCDs for fault protection in adibatic equasion

[samn420]

Hi all

Was looking in to the adibatic equasion as our company will not let us add on to a Ring circuit with 1mm cpc..

I want to give some evidence as to why it may not be an issue.

My question is;

If the circuit is protected by an rcd can I replace fault current in the adibatic equasion with 30ma as that is all the rcd will potentaly allow to flow down the cpc?

Thanks

 

[mainline]

if the circuit is RCD protected ,the maximum ZS is 1667 ohms

Depends on the type of rcd it is.

Below 200 ohms may not be stable.

 

[newfutile]

Could you not add a fused spur to provide protection for the spur?
An mcb will always trip faster than an rcd in the magnetic(instant) part of the curve.
Its all about the let though energy ,how much current is flowing thought the cable an the time its flowing,this is what heats the cable and more importantly the insulation.

 

[Yellowhammer]

Could you not take an r1+r2 for the ring, add the proposed lengths for the extension, divide that by 4 for, add the Ze to get a theoretical Zs and establish a theoretical PEFC. Use fig 3A4 or assume that above a PEFC of 160A a type B 60898/61009 is going to go in <0.1 and then plug in your PFC and 0.1 to the adiabatic and get something smaller than 1.5, given I imagine a 6KA figure is substantially greater than the PEFC you're going to see?

Or maybe I am well out