Rockwell Automation T80008 Application Note MCB Discrimination - Manual (Page 4)

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AN-T80008 MCB Discrimination
Issue 2 Feb 07 AN-T80008 4
Example analysis
If the circuit breakers used were ETA 2210-S2 (fast acting) 10A (see Figure 3) then at two times the
MCB rating i.e. 20A, it would take 10 seconds to trip the MCB.
If one of the MCBs in the example above were subjected to an overload, resulting in a load of 20A in
one branch, then the power pack total load is increased to 40A. At 40A the power pack goes into
protective shutdown after 700mS and hence will shutdown before the branch MCB has opened. A
larger overload will result in protective shutdown after 200ms (see Figure 2)
Figure 3 Characteristics of ETA Thermal-magnetic circuit breaker 2210-S2 (fast acting)
Power unit
10A
10A
10A