Application Data; What Is Discrimination?; How To Read The Discrimination Tables; Discrimination Table - TERASAKI TemPower 2 ACB Manual

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Application Data

What Is Discrimination?

Discrimination, also called selectivity, is the co-ordination of protective devices such that a
fault is cleared by the protective device installed immediately upstream of the fault, and by
that device alone.
Total discrimination
Discrimination is said to be total if the downstream circuit breaker opens and the upstream
circuit breaker remains closed. This ensures maximum availability of the system.
Partial discrimination
Discrimination is partial if the above condition is not fulfiled up to the prospective short-
circuit current, but to a lesser value, termed the selectivity limit current (
Above this value both circuit breakers could open, resulting in loss of selectivity

How To Read The Discrimination Tables

Boxes containing the letter "T" indicate total discrimination between the relevant upstream and downstream circuit-breakers. Total
discrimination applies for all fault levels up to the breaking capacity of the upstream or the downstream circuit breaker, whichever is
the lesser.
For the other boxes, discrimination is either partial or there is no discrimination.
Worked Examples
Q (1) A main switchboard requires a 1600A ACB feeding a 400A MCCB.The fault level is 65kA. What combination of
protective devices would provide total discrimination?
A (1) A TemPower2 ACB AR216S feeding a TemBreak2 S400GJ would provide total discrimination up to 65kA. See page 65
Note: Discrimination would be total whether the TemPower2 ACB
(1s) = Ics. Most other ACBs have Icw(1s) < Ics .
64
X
upstream
circuit
breaker
X
downstream
circuit
breaker
I
s).
fault
current
had an integral or external protection relay because Icw

Discrimination Table

Upsream: TemPower2 ACB with or without Integral Protection Relay
Downstream: TemBreak2 MCCB
65