Building Drive Fuses

Bussmann makes a FWH-70A and a FWH-70B. It appears from the datasheet that the FWH-70B is a faster fuse, by up to 44%. There is a complete datasheet for the FWH-70B but none for the FWH-70A. These two fuse types may be very slightly different in size. The FWH-70A may be the original design that is being replaced with the newer FWH-70B.

The Bussmann WEB site indicates that suitable substitutes for the Ferraz Shawmut A50QS70-4 are the FWH-70A and FWH-70B. The melting time for the A50QS70-4 fuse is about 3.4% slower than for the Bussmann FWH-70A.

The Ferraz Shawmut A50QS70-4 is a suitable substitute for the Bussmann FWH-70A, even the physical size seems identical.