Colin McDonnell asks this question, which concerns the energy let-through of one of Schneider Electric’s Compact NS MCCBs. It has been answered by Schneider Electric (Theme – Distribution Equipment):
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Question: Can you please advise about the I2t energy let-through and tripping time of an NSX160F MCCB fitted with a Micrologic 2.2 40A trip unit set at Io = 25A / Ir = 1xIo / Is = 5 x Ir on a fault current of 3kA.
Answer: Firstly, for a 40A Micrologic 2.2 trip, the circuit breaker used should be the NSX 100F frame.
Secondly, the time and current tripping curves (and other characteristics) of NSX MCCBs are attached (use link below). The fault level 3kA is below the I2t curves, so the time and current tripping curves for the 40A Micrologic 2.2 must be used.
The stated fault level 3kA is 75x 40A trip rating. This represents a tripping time less than 10ms. The cable KS must be greater than 90,000 I2t.
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