Adiabatic question

[Paul_K]

Hi guys,


I have brain freeze and need some help!


I'm currently looking to run in a radial socket outlet circuit to a bedroom from a spare way in the consumer unit. The total circuit length will be approx 10 meters of 2.5 t&e. The supply is a TNC-S arrangement with a Ze of 0.13ohm (by direct measurement). The circuit protection is by way of a 20amp Type B BSEN60898 mini circuit breaker. NO RCD!!


Normally I would just follow the typical values in the OSG. This time though, I decided to just calculate it... Have to keep doing it once in a while or I'll forget!! :-/
The cable itself is fine (obviously) until I check the cpc size using the adiabatic equation. Can someone tell me if I've got this right? :-/


Ze = 0.13


R1+ R2 = 0.23 (adjusted for temperature @ 10 x 19.51 x 1.2)


Zs = Ze + R1 + R2
= 0.36


230/0.36
= 639A


K factor = 115
Assuming instantaneous time of 0.1sec


S = sroot(639*x0.1)/K
= 1.76??


Thanks in advance!

 

[GLENNSPARK]

i see where 639A has come from...

but you are looking for the fault current needed to acheave a .1 to 5 sec disconnection time...aren`t you...it aint 639A...is it

 

[Paul_K]

I can't believe that slipped past... Embarrassed now! lol :-/

 

[Guest55]

looks like youre gonna need a cable with at least a 1.75mm cpc , which will be 6mm t&e ;-)


or maybe look at time current graphs for a 20a mcb ............


which will probably end up giving you a min cpc size of around half that.

 

[ipf]

Don't forget the RCD.

 

[Paul_K]

Uhuh... Please continue!It's entertaining!

 

[Paul_K]

What does an RCD do anyway?

 

[GLENNSPARK]

What does an RCD do anyway?

lolffs....lol....lol..

 

[MDJ]

What does an RCD do anyway?

It can help you learn how to play the Piano

 

[ipf]

What does an RCD do anyway?

Runs Current Down

 

[Paul_K]

Can I run it under a carpet though?

 

[MDJ]

Lets end this now, a 2.5mm2 cable to a socket as a single radial to a bedroom 10 mtrs away from the dist board?? yes okay get on with it, 16 amp mcb and you will be fine, fluck the calculations on this occassion.

 

[Paul_K]

What is a semi enclosed fused to BS3036 .. Should I touch this stuff?

 

[GLENNSPARK]

What does an RCD do anyway?

it makes red current drinks....

 

[Pete999]

Residual clot device