Adiabatic equation and bonding

[GaryM]

Not got it with me at the moment but look at chapter 54

 

[DaveyD]

543.1.1

 

[Deleted member 26818]

Can somebody have a look at this and tell me which tree I'm barking up?

Using the Adiabatic equation to determine the required size of main bonding and therefore the size of supplementary bonding.

Ze = 0.18

PFC = 1.3 kA

Fuse type 1361 IIa

S = square root (1300 x 1300 x 0.1) /115

= 3.57

Is that right? Seems like a very low value for main earth

No nearly, but not quite.
Should be: S = √(1100 x 1100 x 0.1) / 115
= 3.03.

 

[MarkieSparkie]

For a BS1361 80A fuse:- from Table 54.2 k=143 and from Appendix 3, fig3.1 1100A @0.1s
S=√(1100[SUP]2[/SUP]x0.1)/143
S=2.43mm[SUP]2[/SUP]

 

[esc]

Good thread on the adibiatic guys. Would any of you know if actually fitting a main earthing conductor on a TT or TN-S is notifiable or not?
Cheers

 

[GaryM]

Would any of you know if actually fitting a main earthing conductor on a TT or TN-S is notifiable or not?
Cheers

Yes, that would be notifiable as it's not listed as an exception, unlike the addition or upgrade of main or supplementary bonding.

Approved Document P

 

[dellboy78]

Maybe a silly question, but what is brb??

 

[malcolmsanford]

BRB = Big Red Book the old BS 7671-2008 befroe the green one came on the 1st Amendment, is now the BGB = Big Green B..... you get my frift

 

[Deleted member 26818]

As far as I'm aware upgrading, replacing or installing earthing and bonding, is not notifiable.

 

[Engineer54]

His wording isnt clear but he mentioned main earth at the bottom of his equation so his intention was selecting the size of bonding conductors in accordance with the calculated size of his earthing conductor.

Using the Adiabatic equation to determine the required size of main bonding and therefore the size of supplementary bonding.



​

Widdler is absolutely correct in what he stated, according to what the OP had posted!!

The adiabatic equation is used for sizing of the earth conductor and protective conductors only, It's ''NOT'' to be used for bonding conductors.


​

 

[Deleted member 26818]

Well with TN-S and TT, you would determine the required CSA of the earthing conductor using the adiabatic equation, and using that value determine the CSA of the bonding conductors.
So technically, the bonding conductors are determined by use of the adiabatic equation.

 

[dellboy78]

Where does the 0.1s disconnection time come from at the top of the thread? Why not 5s?

 

[malcolmsanford]

I'm the same as you as in the OP it gives us the type of fuse but not the size, but as it's a BS 1361 it would not be above 100amp

The Ze is 0.18 and so the I2 is 230/0.18 which actually gives you 1277.77 but the OP rounded it up to 1300.

If you look at appendix 3 on the BGB Fig 3A1 would equate to a BS 1361 fuse and if you took the 63/80 amp ratings then it would take 820/1100 amps respectfully to trip those devices in 0.1 seconds.

As Fault current would be 1300 then that 0.1 is the value you use for t in the equation.

 

[telectrix]

Where does the 0.1s disconnection time come from at the top of the thread? Why not 5s?

from the time/current curves for fuses. at 1300A the fuse should blow in 0.1 secs.

 

[dellboy78]

Thanks

 

[GaryM]

Widdler is absolutely correct in what he stated, according to what the OP had posted!!

The adiabatic equation is used for sizing of the earth conductor and protective conductors only, It's ''NOT'' to be used for bonding conductors.


​

Yes, I know that.
I stated the the South Sparks wording wasn't clear, not Widdlers.
The final line of the OP suggested he was calculating the minimum size of an earthing conductor so he could size a bonding conductor from that.

 

[i=p/u]

Osg green book will help you all out,