How to Use an Electrical Voltage Meter

The voltmeter is an easy test instrument to master. Although there are stand-alone voltmeters, in most cases they are just one function on multifunction test instruments like a DMM (digital multimeter) or on a VOM (volt-ohm-millimeter,) the older analog predecessor of the DMM. The voltmeter as a stand-alone test instrument comes in three configurations, an AC (alternating current) voltmeter, a DC (direct current) voltmeter, or a combination AC/DC voltmeter. Everyone who works with electricity must learn to use a voltmeter correctly, whether it's a stand-alone meter or just one function of a DMM or VOM.

Instructions

1. Locate a blown cartridge fuse with the AC voltmeter by placing one test probe on each of the brass end caps. If the fuse is blown, line voltage will read on the meter. A good fuse will read "0" volts. Cartridge fuses are used as OCPD (over current protection devices) for high current loads such as central air conditioning units, deep well pumps, electric furnaces, etc.; in older homes, they are also used in the main service disconnect switch. This simple test will tell you in seconds if a blown fuse is causing your problem.

2. Test a malfunctioning receptacle by placing one of the probes in the "Line" slot, the short slot, of the receptacle and place the other probe in the "Ground" hole. If you read line voltage, the problem is an open neutral somewhere between that receptacle and the service panel. If you have no voltage between line and ground, the problem is an open "hot" wire somewhere between the receptacle and service panel. If you have voltage, but it's significantly lower than line voltage, the problem is a loose connection somewhere between the receptacle and the service panel.

3. Check a light switch by placing one probe on each of the brass screws, if you read line voltage, the switch is defective. If there's no voltage present across the switch, place one probe on the box ground and the other probe on the black wire coming from the service panel, if you still read "0" volts, the problem is an open hot wire somewhere between the switch and the service panel. If voltage is coming into the box, the problem is an open circuit somewhere between the switch and the neutral connection on the panel.

4. Check circuit breakers by putting one probe on the circuit breaker terminal and the other probe on the panel ground. If the meter reads line voltage, the breaker is good.

References

• Facstaff.bucknell.edu: Measuring Voltage
• Wisc-online.com: Analog Voltmeter Operations
• Kpsec.freeuk.com: Meters

Resources

• Allaboutcircuits.com: Voltmeter Usage