The maximum ZS for a type B 6 amp mcb to BS EN 60898 is listed as 5.87 ohms by my calculations (and NICEIC , iCertify) this is incorrect.
6 x 5 (from 3-5 current trip) = 30 , 230/30= 7.666666 (I believe this is correct with BS7671 brown book , 7.66666 x 0.95 (cMin)=7.283333 x 80% (conductor temperature adjustment) = 5.826666
therefore 5.82 should not be exceeded .
Thank you, this has already been corrected.
I've just checked Page 145 of the latest version ("Eighth Ed Reprinted with minor corrections 2022"), and it says '5.83' which matches your calculation (give or take whether you believe you can round up or not).
I agree it was incorrect (5.87) in the original 2022 "Eighth Edition" and also P 131 in the 2018 Seventh Edition.
Your approach is spot-on. Formula from Appendix 3:
And for a B6, Ia = 5 × 6 = 30
so Zs(m) ≤ 0.8 × 0.95 × 230 ÷ 30 = 5.82666...
Round up or down? I can see both sides of this argument, but since it's a "rule of thumb" and given the measurement conditions and resolution and accuracy of most loop test instruments,rounding up in this case probably won't make much difference out there in the real world.
Thank you, this has already been corrected.
I've just checked Page 145 of the latest version ("Eighth Ed Reprinted with minor corrections 2022"), and it says '5.83' which matches your calculation (give or take whether you believe you can round up or not).
I agree it was incorrect (5.87) in the original 2022 "Eighth Edition" and also P 131 in the 2018 Seventh Edition.
Your approach is spot-on. Formula from Appendix 3:
And for a B6, Ia = 5 × 6 = 30
so Zs(m) ≤ 0.8 × 0.95 × 230 ÷ 30 = 5.82666...
Round up or down? I can see both sides of this argument, but since it's a "rule of thumb" and given the measurement conditions and resolution and accuracy of most loop test instruments,rounding up in this case probably won't make much difference out there in the real world.
