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Remember there is no voltage drop across a straight piece of wire. Some plug-type fuseholders have test
points built in to allow you to check the voltage. To check for voltage on a clip-type fuseholder, check
each of the clips. The advantage of using a voltmeter to check for an open fuse is that the circuit does not
have to be deenergized and the fuse does not have to be removed.
WARNING
PERSONNEL MAY BE EXPOSED TO HAZARDOUS VOLTAGE
Safety Precautions When Checking a Fuse
Since a fuse has current through it, you must be very careful when checking for an open fuse to
avoid being shocked or damaging the circuit. The following safety precautions will protect you and the
equipment you are using.
Turn the power off and discharge the circuit before removing a fuse.
Use a fusepuller (an insulated tool) when you remove a fuse from a clip-type fuseholder.
When you check a fuse with a voltmeter, be careful to avoid shocks and short circuits.
When you use an ohmmeter to check fuses with low current ratings, be careful to avoid opening
the fuse by excessive current from the ohmmeter.
Q21. What are three methods for determining if a fuse is open?
Q22. You have just checked a fuse with an ohmmeter and find that the fuse is shorted. What should you
do?
Q23. You have just checked a 1/500-ampere fuse with an ohmmeter and find it is open. Checking the
replacement fuse shows the replacement fuse is open also. Why would the replacement fuse
indicate open?
Q24. How could you check a 1/500-ampere fuse with an ohmmeter?
Q25. List the safety precautions to be observed when checking fuses.
REPLACEMENT OF FUSES
After an open fuse is found and the trouble that caused the fuse to open has been corrected, the fuse
must be replaced. Before you replace the fuse, you must be certain the replacement fuse is the proper type
and fits correctly.
Proper Type of Replacement Fuse
To be certain a fuse is the proper type, check the technical manual for the equipment. The parts list
will show you the proper fuse identification for a replacement fuse. Obtain the exact fuse specified, if
possible, and check the identification number of the replacement fuse against the parts list.
If you cannot obtain a direct replacement, use the following guidelines:
Never use a fuse with a higher current rating, a lower voltage rating, or a slower time delay
rating than the specified fuse.
