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In SANS 10142-1:2020, there are 2 tables with same description but different values: Table 6.28(a) and 6.28(b). Why the difference, when should which table be used? It can make a big difference in price when big building is involved with 800A circuit breakers.
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There is a difference in table description as can be seen from the headings pasted below from SANS
The explanation and calculations for Table 6.28(b) precedes the table
The clause below extracted from SANS sums up the difference between the 2 tables
For most general purpose circuit breakers it would suffice to use
10 multiply by the rated nominal current In for the instantaneous
tripping point of the circuit breaker, however the precise number could
be obtained from the manufacturer's information or from the
instantaneous current setting of adjustable circuit breakers, thus
Im=In x 10
Table 6.28(a) — Minimum size and maximum length of copper earth continuity conductors rated at phase conductor
diameter, for general purpose circuit-breaker
Table 6.28(b) — Minimum size and maximum length of copper earth
contuinity conductors rated at 50 % of phase conductor diameter, for
general purpose circuit-breakers with instantaneous tripping current
Im = 10 × In -
Tnx very much, that gives me more clarity. I appreciate.Comment
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