What are the difference between C-Curve and D-Curve for
MCB's.
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Answer Posted / simon
Awesome thread with a lot of almost correct and mostly
correct answers.
The challenge is knowing to which standard a particular
breaker was manufactured.
AS/NZS 4898 specifies:
B Curve between 3 In and 5 In
C Curve between 5 In and 10 In
D Curve between 10 In and 14 In
This was an update to AS 3947.2 which specified:
B Curve between 3.2 In and 4.8 In
C Curve between 7 In and 10 In
D Curve between 10 In and 14 In
The application notes in #11 and #13 are pretty much spot on.
Now lets assume we're only using AS/NZS 4898 breakers.
Lets assume we're using a Clipsal C60 10A B curve breaker.
The breaker should operate electromagnetically (<0.2s)with
an inrush current greater than 30A (3 x 10A).
The same 10A breaker however with 15A of current will not
trip electromagnetically but will trip thermally between 30
and 600 seconds after load is applied.
A C curve breaker of the same type should not operate
electromagnetically at either 15A or 30A. It should operate
thermally between 30 and 1000 seconds after a 15A load is
applied and between 6 and 50 seconds after a 30A load is
applied.
Note the distinct difference between and instantaneous /
electromagnetic trip and a delayed / thermal trip.
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