Overcurrent protection, Ib ≤ In ≤ Iz Selected according to the coordination rule: the rated current (In) of the protective device must be greater than the design current and less than the cable's carrying capacity. The tool recommends the smallest standard value in this range.

Ib ≤ In ≤ Iz and I₂ ≤ 1.45·Iz
Example calculation: With a design current Ib = 38 A and cable capacitance Iz = 63 A, the smallest standard value of 40 A is selected within the range 38 ≤ In ≤ 63.

Fuse/Circuit Breaker Selection (Ib ≤ In ≤ Iz)

Determine the appropriate standard rated current (In) based on the design current and cable capacity (overcurrent protection coordination).

The recommended rated current is In
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Rule
Ib ≤ In ≤ Iz
Notes: IEC/HD 60364-4-43 coordination rule: Ib ≤ In ≤ Iz and I₂ ≤ 1.45·Iz. Since I₂=1.45·In in standard MCBs, the condition In ≤ Iz also satisfies the second condition. The smallest value that satisfies Ib is selected from among the standard rated currents. The short-circuit breaking capacity should also be checked.
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How is it calculated?

  1. Enter the design (load) current (Ib).
  2. Enter the cable carrying capacity (Iz).
  3. Press Calculate; a suitable standard rated current will be suggested.

Frequently Asked Questions

How to select the fuse's rated current?
According to the rule Ib ≤ In ≤ Iz, the rated current is selected to be greater than the load current and less than the cable capacitance (IEC/HD 60364-4-43).
How many mm² of cable is needed for a 16A fuse?
The cable's load-carrying capacity (Iz) must be greater than 16 A depending on the laying conditions; the cross-section is determined by the laying method and the environment. Check with the Ampacity tool.
Should the short-circuit breaking capacity also be checked?
Yes, the breaking capacity (Icu) of the selected device must be greater than the potential short-circuit current.

Related tools and services

This tool and its content are for general informational purposes only; they do not constitute a binding inspection/declaration of conformity. Definitive results will be determined through on-site inspection in accordance with relevant legislation and standards. Get a quote →