📝 How it works:
Estimate the selectivity (discrimination) of two series protective devices via the rated-current ratio (gG rule of thumb 1.6:1).
Fill in the fields below and click "Calculate".
Estimate the selectivity (discrimination) of two series protective devices via the rated-current ratio (gG rule of thumb 1.6:1).
Fill in the fields below and click "Calculate".
Discrimination (selectivity) means that on a fault only the nearest (downstream) device trips, not the upstream one. It depends on the time-current curves.
As a first estimate in the overload range the rated-current ratio is used: for gG fuses the rule of thumb is In(upstream) / In(downstream) ≥ 1.6 : 1. With miniature circuit breakers (MCBs) selectivity is only guaranteed up to the manufacturer's selectivity limit current Is – in the short-circuit range MCBs are often not selective.
Note: for a binding statement – especially on short-circuit selectivity – the manufacturer's selectivity table is decisive.
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