Help please: 2365 Level 3 Unit 305 Design Project

[Stuart27]

So i'm a little confused at the min with the adiabatic equation to verify minimum cpc csa..

My circuit is a 16A socket in 2.5mm singles (bunched in conduit)
I worked the Zs out to be 0.26Ω

To work out the minimum cpc csa to satisfy ADS i'm not sure if I should use the Ipf of the circuit (230v/0.26Ω=884.6A Ipf) or do I use the minimum fault current capacity of the device i'm using (B16, so 80A minimum fault current)?

Also, should I use the max disconnection time 0.4s? or 0.1s disconnection time from fig 3A4(page 370 in the 18th regs)

If using my calculated Ipf and device rating 0.1s disconnection time from the table 3A4 it works out to be minimum cpc csa is 2.4mm.. which means i'd have to use a minimum 2.5mm cpc with a 2.5mm line conductor?

 

[westward10]

The cpc must be able to withstand the fault current to disconnect the circuit without suffering thermal damage. This possible fault is not limited to the furthest point of circuit where you have your Zs it could occur anywhere.

 

[H]

Would the disconnection time permitted depend on the earthing arrangement?

 

[Stuart27]

The cpc must be able to withstand the fault current to disconnect the circuit without suffering thermal damage. This possible fault is not limited to the furthest point of circuit where you have your Zs it could occur anywhere.

Interesting... I see your point, if the fault occurred 1m from the board the fault current would be much higher.. you've only confused me more though with regards to which values to use for this equation

Would the disconnection time permitted depend on the earthing arrangement?

It's a TN-C-S system, the permitted disconnection time for this circuit is 0.4 seconds, but the disconnection time for a B16 at 80A fault current is 0.1s, i'm not sure which of these values I should use for the adiabatic equation..
I'm guessing the 0.1 second value, since that's what's actually going to flow.

 

[Stuart27]

Cracked it, good old JW covers it in one of his videos.

 

[ackbarthestar]

A simple approach might be
furthest point use Zs and 0.1s (minimum fault current to disconnect circuit)
nearest point use Ze and 0.4s (very basic approximation for maximum allowable fault current before cable melts damage to protective device)
from the formula:
sq S * sq K > Sq I * t ie characteristics of the cable must be greater than the energy let through of the fault
( adiabatic formula transposed)

 

[Jay 1987]

Cracked it, good old JW covers it in one of his videos.

Lol I’m watching a lot of jw these days ....

His very clear