16mm T+E and adiabatic equation

[rs250250]

Evening all,
I have a question regarding calculation of CPC on a 16mm T+E and wondered if you could help at all.

I have done a board change and the supply is via a 16mm T+E. It appears the CPC is 6mm and therefore I did the adiabatic equation to confirm if the CPC is adequate.
The circuit is fed via 60A BS1361 type 2. The issue I have had is that BS1361 is no longer listed in appendix 3. Does any one know what table in appendix 3 should be used? Looking through the green book it appears that the equivalent would be BS88-3?

I therefore did the following calc. S = √ISq t/k
TN-S system
My Ze was 0.12ohms so fault current is 230/0.12=1916A
K value was 115 as cables bunched with other circuits (taken from table 54.3)
1916A squared = √3671056 x 0.1S disconnection time. (i assume due to the fault current and reference to table 3A1 it would be 0.1S) = 605.892/115 = 5.26mm CPC

Therefore 6mm would suffice.

If anyone can confirm or correct this I would be grateful. I still find the idea of using anything so small as uncomfortable, but if it complies then I am happy.

Many Thanks

 

[Guest55]

you dont use Ze for the fault current calc in a adiabatic check , you use Zs , or in this case the Z at the DB.
and yes bs 88 is the "new" 1361

 

[rs250250]

you dont use Ze for the fault current calc in a adiabatic check , you use Zs , or in this case the Z at the DB.
and yes bs 88 is the "new" 1361

Thanks Biff55, my mistake, it was the Zdb taken at the board, nice to know I am on the right track

 

[Deleted member 26818]

You need to obtain a copy of the pre-amendment Regulations, or look up on google for the time/current characteristics.
BS88-3 has replaced BS1361, but the time/current characteristics are different.

 

[rattlehead85]

You need to obtain a copy of the pre-amendment Regulations, or look up on google for the time/current characteristics.
BS88-3 has replaced BS1361, but the time/current characteristics are different.

Spot on with that. It is essential you locate the time / current characteristics for the fuse installed as this may well be the difference between a satisfactory outcome or a non compliant supply requiring upgrading which another spark will gladly shoot you down on if he prooves your calculations were incorrect.