Can't seem to find the answer, 18th edition tommorow ; )

[stephen fenton]

A circuit with a 10mm 70*C thermoplastic copper live conductor has a maximum final temperature of 160*C. If a fault current of 600A flows through the conductor, the time taken to reach the final temperature would be.... ? got all the rest just cant seem to locate this one! cheers in advance.

 

[telectrix]

use the adiabatic.

 

[Shoei]

A circuit with a 10mm 70*C thermoplastic copper live conductor has a maximum final temperature of 160*C. If a fault current of 600A flows through the conductor, the time taken to reach the final temperature would be.... ? got all the rest just cant seem to locate this one! cheers in advance.

Check out 434.5.2

 

[telectrix]

t = k²S²/I²

 

[stephen fenton]

nice one Shoei i shall attempt that formula now cheers

 

[rompling]

Exact question in the 18th exam I took today !!
Did you do it too ?
I thought you title said your taking it tomorrow

 

[stephen fenton]

nice one Shoei i shall attempt that formula now cheers

5 seconds does that seem about right

 

[stephen fenton]

t = k²S²/I²

yeah that's the one

 

[stephen fenton]

Exact question in the 18th exam I took today !!
Did you do it too ?
I thought you title said your taking it tomorrow

i am it was a revivision paper lol nice one will study it some more now ; )

 

[telectrix]

what value did you use for k? using 115, i get 3.67 secs.

 

[telectrix]

5.7 secs using 143 for k.

 

[stephen fenton]

I asked this question as i don't really look at the regulations too much as the technical guys in the office do the groundwork for installations and such. Obviously I'm familiar with the do's and don'ts but the more in-depth stuff, well its been a while but i have enjoyed it and I'm going to keep up to date with this one lol. Oh by the way there has been minor changes already they haven't been released yet but an amendment is definitely on the horizon.​

 

[stephen fenton]

5.7 secs using 143 for k.

yeah got that but they gave us four outcomes which was 0.4s/1.92s/3.67s/5s i didn't stipulate this in the beginning but 5s I'm guessing they have just rounded it off.

 

[stephen fenton]

what value did you use for k? using 115, i get 3.67 secs.

k squared would be 160*C squared /maximum final temperature/25600

 

[Deleted member 26818]

5.68s.
Looks like they used 115 for k.
Though there’s nothing in the question to tell us whether it’s single core or part of a cable.

 

[Shoei]

nice one Shoei i shall attempt that formula now cheers

You're welcome, good luck with the exam

 

[Deleted member 26818]

It’s unlikely that they would round up an answer, if they have other answers to 2 decimal points.
Just have to calculate using both values, and if an outcome matches one of the answers, then that’s the answer.

 

[stephen fenton]

You're welcome, good luck with the exam

thank you

 

[PEG]

The wording is always a bit woolly,but it is phrased in the singular...

 

[telectrix]

k squared would be 160*C squared /maximum final temperature/25600

k is either 115 or 143, depending if its single core cable or multicore. 160 is the temp.