A21. Visual inspection, indicators, and using a meter.
A22. Put it back in the circuit. A good fuse will have zero ohms of resistance.
A23. The ohmmeter causes more than 1/500 ampere through the fuse when you check the fuse, thus it
opens the fuse.
A24. Use a resistor in series with the fuse when you check it with the ohmmeter.
A25. Turn the power off and discharge the circuit before you remove fuses. Use a fuse puller (an
insulated tool) when you remove fuses front clip-type fuse holders. When you check fuses with a
voltmeter, be careful to avoid shocks and short circuits.
Not acceptable-wrong style
Substitute #3-smaller current rating
Substitute #1-identical, except higher voltage rating
Not acceptable-lower voltage rating
Not acceptable-higher current rating
Substitute #2-Faster time delay rating
A27. Check for the proper type of replacement fuse and proper fit.
A28. Be sure the power is off in the circuit and the circuit is discharged before replacing a fuse. Use an
identical replacement fuse if possible. Remove any corrosion from the fuseholders before
replacing the fuses.
A29. Improper fuse, corrosion, improper fit, and open fuse.
A30. Frame, operating mechanism, arc extinguishers, terminal connectors, and trip element.
A31. Thermal, magnetic, and thermal-magnetic.
A32. The thermal trip element makes use of a bimetallic element that bends with an increase in
temperature or current. The bending causes the trip bar to be moved releasing the latch.
A33. A circuit breaker that will trip even if the operating mechanism is held ON.
A34. A circuit breaker that can be overridden if the operating mechanism is held ON.
A35. In current sensitive or nonemergency systems.