adiabatic equation reg 543.1.3

[piz]

Can any one help please
on a tncs system (PME)
100amp main fuse bs1361 100amp
I am trying to work out the maths for the earthing is there a simple way all looks a little confusing
S is the csa of the conductor 25mm
I is ???
t is page 244 the table says 630A
K = ??
so 630A squared x 5 (5sec disconection time
Now I am stuck
Cheers

 

[Guest 004]

K is the value of the metal, whether it is copper or ally, from memory I cant remember what the values are, is root 3 used as well?, remember doing at college, but never applied it. Give me all the details you have, and I will run through Amtech for you.

 

[Guest 004]

If you know S = 25mm, then why are trying to work it out??
S is the figure you need to work out
I = current (squared), so its 100 squared x5
square root of
then divide by K
then that give S, (size of the earth)

 

[piz]

sorry well confused now s is the size of the meter tails

 

[yellowvanman]

If your looking to size the main earth and the cut out is the protective fuse:

I is the current required to disconnect, in t seconds
page 244 current to blow a 1361 100A fuse in 5 secs = 630A
t = 5 secs (as its over 32A)
K is from the tables on Page 129, if the earth cable is bunched with the tails then Table 54.3, 70degrees Thermoplastic and copper
K = 115

Therefore S= Sq Root(630 x 630 x 5)/115 = 12.25

So you need to use a 16mm earth!

 

[Guest 004]

deleted my error in the equation........

 

[Guest 004]

ar feck it, just pull in a 90mm you will be ok then

 

[Martin Bradley]

S= size of conductor nominal conductor size mm2
I = fault current
t= time it takes, to operate device
K= thermal constraints of cable, temperature coefficient and heat capacity of cable.

 

[piz]

thanks yellowvanman
well confused now I have got that printed and in with the regs what I am trying to work out is the bonding sizes to water and gas
ie if I change a cu and I am trying to work out if I leave a 6mm cable is this ok??
Normal practise I upgrade to 10mm but customer has asked me to calculate because previous spark sais 6mm ok o/s/g has pictures of 10mm
sorry to confuse the matter what I am after is calculation for equopotential bonding many thanks

 

[piz]

0.11 ohms

 

[Guest 004]

thanks yellowvanman
well confused now I have got that printed and in with the regs what I am trying to work out is the bonding sizes to water and gas
ie if I change a cu and I am trying to work out if I leave a 6mm cable is this ok??
Normal practise I upgrade to 10mm but customer has asked me to calculate because previous spark sais 6mm ok o/s/g has pictures of 10mm
sorry to confuse the matter what I am after is calculation for equopotential bonding many thanks

are you really a spark?................oh you must be your a member of the sparky arms

sorry could not resist

 

[yellowvanman]

For PME system you've no choice on bonding size - Table 54.8 (Page 134) - 10mm

 

[Martin Bradley]

im getting 6mm as well chap

 

[Martin Bradley]

but yes bond with 10mm

 

[tony mc]

With PME the bonding conductor is sized by the size of the DNO supply neutral conductor.

If the neutral is up to 35 mm you need 10mm bonding.