Max zs equations

[brizospark]

Does anyone have the equations for working out max zs for 60898 mcb's and also older mcb's and fuses?

I know these values are stated in BS7671 / OSG but sometimes these are not at hand.

Thanks

 

[IQ Electrical]

Does anyone have the equations for working out max zs for 60898 mcb's and also older mcb's and fuses?

I know these values are stated in BS7671 / OSG but sometimes these are not at hand.

Thanks

BS60898 Type B, C and D is a current multiplier of 5, 10 and 20 respectively.

I can't remember BS3871, I'll have to dig it out!

 

[malcolmsanford]

View attachment Zs values for older protection devices.pdf

This is for BS 3871

 

[IQ Electrical]

Does anyone have the equations for working out max zs for 60898 mcb's and also older mcb's and fuses?

I know these values are stated in BS7671 / OSG but sometimes these are not at hand.

Thanks

Right, I found the values:

BS60898 Type B, C and D is a current multiplier of 5, 10 and 20 respectively.

BS 3871 Types 1, 2 and 3 is a current multiplier of 4, 7 and 10 respectively-type 4 were manufacturer specific.



So now, you can work out the BS7671 Maximum allowable Zs for one of the above devices by Ohms Law:

Take a BS60898 10A type C: R=V/I 230/10X10 = 2.3 Ohms

 

[brizospark]

Thanks again IQ you really do know your biscuits!!

 

[ezzzekiel]

32amp type b at 5x its rating = 160
dive by the voltage 230/160 = 1.44

as stated above c=x10 d=x20

 

[ELEKTRIC]

MAXIMUM EARTH FAULT LOOP IMPEDANCE (EFLI) ZsMAX​

Example:
For a 32A type B MCB on a supply of 230V:
ZsMAX = U0 / 5x In = 230V / 5x32mA = 1.44 Ohm;
** So, for a 32A type B MCB the maximum Earth Loop Impedance is ZsMAX = 1,44 Ω

 

[ezzzekiel]

which looks an awful lot like the examples posted

 

[ohmslaw]

Just to let you know that there is another way to work out the Max Zs for BS60898/61009 devices. All you have to do is divide Btype/46 Ctype/23 and Dtype/11.5 instead of all the other complicated equations.
Rgds, ohmslaw

 

[IQ Electrical]

Just to let you know that there is another way to work out the Max Zs for BS60898/61009 devices. All you have to do is divide Btype/46 Ctype/23 and Dtype/11.5 instead of all the other complicated equations.
Rgds, ohmslaw

You should show an example, maybe on a B 32?

 

[ohmslaw]

No problems:

B 32 46/32= 1.44ohms

C 32 23/32= 0.72ohms

D 32 11.5/32= 0.36ohms

As you can see the device max Zs rating basically halfs as you change from B type through to C type.

Rgds, ohmslaw

 

[IQ Electrical]

It just keeps it nice and clear for anyone learning the theory

 

[telectrix]

i calculate it using Zs(max.) = 230/(In x F), where F=5 for Btype. 10 for C, 20 for D. ssssssimples

 

[IQ Electrical]

i calculate it using Zs(max.) = 230/(In x F), where F=5 for Btype. 10 for C, 20 for D. ssssssimples

I have to agree, 5, 10, 20 is easier to remember than 46, 23 and 11.5 but each to their own..

 

[telectrix]

i suppose if you just remember 46, the halve it for C, and halve again for D. none of the sums are einstein level.