Adiabatic equation

[Paul505]

When plotting your PEFC against the times for your protective device in appendix 3 and your trying to work out an exact time, is it better to round it off to the nearest higher time frame?....As this will give you a slightly higher csa when working out your min acceptable size, which is better than selecting a lower time frame. I haven't carried out this equation recently.

Any replies would be appreciated.

 

[Guest55]

depends how slow the device operating time is.

around 0.5 secs or less theres hardly any difference in the final figure.
nearer 5 secs i'd be using the exact graph time line.

 

[GLENNSPARK]

yes...do your PFC....
check that against the time current tables in your book...then if your still good...its PFC squared X 0.4=
you apply the square root to the answer to the above....

- - - Updated - - -

depends how slow the device operating time is.

around 0.5 secs or less theres hardly any difference in the final figure.
nearer 5 secs i'd be using the exact graph time line.

but its 0.4 AND 5 secs now in the BGB biff..

 

[Paul505]

Cheers Biff.... Ive just been going through cable calcs recently as I'm a bit rusty with certain bits and I just wanted to make sure I was right.
Thanks for the reply anyway

 

[Paul505]

yes...do your PFC....
check that against the time current tables in your book...then if your still good...its PFC squared X 0.4=
you apply the square root to the answer to the above....

- - - Updated - - -

but its 0.4 AND 5 secs now in the BGB biff..

If your time worked out to be roughly 0.35s but you wasn't 100% sure would you shift upto 0.4s rather than the other way? I would shift up to the higher time....

 

[GLENNSPARK]

If your time worked out to be roughly 0.35s but you wasn't 100% sure would you shift upto 0.4s rather than the other way? I would shift up to the higher time....

yes...
work it as between 0.4 and 5 secs....

 

[Sintra]

Your time is obtained from the graphs in the BGB as different devices have different characteristics at the measured fault current.

 

[Paul505]

Cheers Glenspark..... right I'm off to feed my little one then off to bed as I don't want to have bad dreams about equations

 

[Paul505]

Your time is obtained from the graphs in the BGB as different devices have different characteristics at the measured fault current.

I get the rest of it already.... Cheers anyway

 

[GLENNSPARK]

actually paul505 its been refreshing to have a half decent thread....
makes a change....