Adiabatic question

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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! :-)
 
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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
 
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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.
 
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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.
 
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Hi Paul as your figure calculated using the adiabatic equation will not get a corresponding figure of t from the time / current graph you can obtain the I2t energy let through figure from your MCB manufacturer, you can then substitute it into the adiabatic equation.
The I2t figure for a crabtree starbreaker 20A type B 6K mcb is 22260 put that figure into the adiabatic .
Square root of 22260 / 115 will give minimum size cpc of 1.3mm.
 
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silverfox1 said:
Hi Paul as your figure calculated using the adiabatic equation will not get a corresponding figure of t from the time / current graph you can obtain the I2t energy let through figure from your MCB manufacturer, you can then substitute it into the adiabatic equation.
The I2t figure for a crabtree starbreaker 20A type B 6K mcb is 22260 put that figure into the adiabatic .
Square root of 22260 / 115 will give minimum size cpc of 1.3mm.
Click to expand...

Thanks for reminding me of this; they list I²t figures in the technical section at the end of their catalogue. As it happens, I generally use Crabtree Starbreaker, but does anyone know whether these figures are typical for other makes of BS 60898 circuit breakers?
 
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I hate this forum!!


One of the reasons I never use it, is there's far too many egotistical smart arses on it who are only here to measure the length on their dicks with each other!


Thanks Silverfox1 for the feedback, it's much appreciated! At least there's someone willing to take the time to give a sensible answer!...........


Now to the admin,


Please delete my account, your forum is a disgrace, and seems only to serve very little purpose other than to serve up illiterate people trying their very best to sound clever!


Tedious and off putting!!
 
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Paul_K said:
I hate this forum!!


One of the reasons I never use it, is there's far too many egotistical smart arses on it who are only here to measure the length on their dicks with each other!


Thanks Silverfox1 for the feedback, it's much appreciated! At least there's someone willing to take the time to give a sensible answer!...........


Now to the admin,


Please delete my account, your forum is a disgrace, and seems only to serve very little purpose other than to serve up illiterate people trying their very best to sound clever!


Tedious and off putting!!
Click to expand...
come on Paul..
i gave you a reasonable answer...
 
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