BS7671 V GN3 MAX Zs Values

[silver surfer]

Not trying to nit pick....but.
Table 41.3 max Zs etc are at 100% values whereas GN3 table B.4 show 80% values but some of the values in GN3 are not even close to being rounded up.
For example a type C 32 amp bsen60898 = 0.72 in regs book
GN3 =0.62 for the same device.

but 0.72x 0.8=0.58 at best ....... thats not really close to being 0.62.

Any clarity?

 

[MarkieSparkie]

Hi Silver Surfer, The values tabulated in GN3 and OSG are not calculated by the simple rule of thumb. They are calculated using a more complicated method (see GN3 B1 and EIDG) that compensates for conductor temperature and yields a more accurate result. These tables are useful in situations where the rule of thumb yields marginal non-compliance, often referring to the GN3 or OSG tables, reveals that by the more accurate method of calculation the device does actually comply.

 

[Chr!s]

Not trying to nit pick....but.
Table 41.3 max Zs etc are at 100% values whereas GN3 table B.4 show 80% values but some of the values in GN3 are not even close to being rounded up.
For example a type C 32 amp bsen60898 = 0.72 in regs book
GN3 =0.62 for the same device.

but 0.72x 0.8=0.58 at best ....... thats not really close to being 0.62.

Any clarity?

Yes your not looking close enough.

Gn3 for a 32 amp states .58, your looking at 30 amp.

Regards Chris