What is the difference between NW40 and NW40b?

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Issue:

What is the meaning of "b" in NW40 and NW40b nomenclature for Masterpact NW breakers?

Product Line:

Masterpact NW ANSI and IEC rated circuit breakers

Resolution:

The original IEC NW40 was standard width. Later they added the double-wide and called it NW40b.
The reverse was true for ANSI breakers; the original was double-wide and when they introduced the single-wide it was called NW40b.
So, "b" in this nomenclature simply indicates the second version and is single-wide for ANSI but double-wide for IEC.