How is the Linergy FC Selection Table for Special Cases from the Prisma P catalog used?

The following table indicates the values of maximum permissible current Inc of the Linergy FC for temperatures inside the switchboard.  These values are for conditions that are not like most installations, where the outside temperature is 40°C and 60°C inside the switchboard.


NSX catalogue LVPED217032EN, 2019. Page E-14.

The maximum permissible current of the circuit breaker must be determined from the temperature derating table published in the product catalog (example above).
After the temperature correction factor of the circuit breakers is considered and the diversity factor applied, the result must be less than the Linergy FC maximum permissible current Inc.


Note that K and RDF are equivalent terms in our case.

Examples:

Example 1: For a Linergy FC with up to 4 x NSX250 3p, installed in a switchboard with 40°C inside temperature, the Inc is 800A.
At 40°C, the correction factor determines the NSX250-TM250D setting to be: 1.00 x 250 = 250A.
The maximum permissible current (RDF = 0.8) for the 4 x NSX250-TM250D units is then:
4 x 250 x 0.8 = 800A
This is equal to the Inc.

Example 2: For a Linergy FC with up to 3 x NSX250 4p, installed in a switchboard with 60°C inside temperature, the Inc is 615A.
At 60°C, the correction factor determines the NSX250-TM250D setting to be: 0.90 x 250 = 225A.
The maximum permissible current (RDF = 0.9) for the 3 x NSX250-TM250D units is then:

3 x 225 x 0.9 = 607.5A

This value is less than Inc; 607.5A < 615A


Background:
RDF is based on IEC 61439-2 section 5.4


Extract from IEC specifications for LV assembly switchboards – In conformity with IEC 61439-1&2 standard; Specifiers Guide, pages 9-10.

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