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ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
AFCIs ARC FAULT CIRCUIT INTERRUPTERS
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AMPS VOLTS DETERMINATION
AMPERAGE MEASUREMENT METHODS
APPLIANCE EFFICIENCY RATINGS
BACKUP ELECTRICAL GENERATORS
BACK-WIRED ELECTRICAL DEVICES
BOOKSTORE - ELECTRICAL
Cadet & Encore Heater Recall
CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
Classified CIRCUIT BREAKER WARNING
CUTLER HAMMER PANEL FIRE
CORROSION in ELECTRICAL PANELS
DEFINITIONS of ELECTRICAL TERMS
DIRECTORY OF ELECTRICIANS
DMM Digital Multimeter HOW TO USE
ELECTRIC METERS & METER BASES
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRIC PANEL AMPACITY
ELECTRIC PANEL INSPECTION
ELECTRIC PANEL MOISTURE
Electric Power Frequency Table
EMF RF FIELD & FREQUENCY DEFINITIONS
ELECTRICAL GROUND SYSTEM INSPECTION
ELECTRICAL SERVICE DROP
ELECTRICAL SERVICE ENTRY WIRING
EMF RF FIELD & FREQUENCY DEFINITIONS
FIRE SAFETY Checklist, CPSC
GFCI PROTECTION,Testing GFCIs AFCIs
HEATING COST FUEL & BTU Cost Table
HEAT TAPE USAGE GUIDE
Hertz - Definitions of KHz MHz GHz THz
KNOB & TUBE WIRING
LIGHTING, EXTERIOR GUIDE
LIGHTING, INTERIOR GUIDE
LIGHTNING PROTECTION SYSTEMS
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
MAIN ELECTRICAL DISCONNECT
MAIN DISCONNECT AMPACITY
MOISTURE SOURCES in PANELS
MURRAY SIEMENS Recall
PHOTOVOLTAIC POWER SYSTEMS
PUSHMATIC - BULLDOG PANELS
REMOTE ELECTRIC POWER, PHOTOVOLTAIC
RUST in ELECTRICAL PANELS
SAFETY for ELECTRICAL INSPECTORS
SE CABLE SIZES vs AMPS
SIEMENS MURRAY Recall
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
UNDERGROUND SERVICE LATERALS
VOLTS / AMPS MEASUREMENT EQUIP
VOLTAGE MEASUREMENT METHODS
WIND TURBINES & LIGHTNING
ZINSCO SYLVANIA ELECTRICAL PANELS
Electrical voltage detection and measurement methods & tools: this article describes the range of equipment or tool choices used to detect or measure voltage and other electrical values. We describe the use of digital multimeters(DMMs), Volt-ohm meters (VOMs), neon testers and other types of voltage detectors used to check for the presence of voltage, to check for live electrical circuits and to measure electrical system voltage and amperage levels.
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Voltage Test Equipment Types: How to Determine Electrical Voltage (240V/120V) using a neon tester, a VOM, DMM, Volt Meter, or Voltage Detector pen
Instruments as simple as the neon-tester shown here or a digital multimeter (DMM), or an analog volt meter (volt-ohm meter) such as those made by Triplett, Fluke, Simpson and Sperry can be used to measure the voltage level between the two power feed lines to confirm the presence of 240 Volt service. (Some versions of this equipment can also be configured to measure amperage or amps).
Using a DMM, analog volt meter, or a neon tester, voltage between the two apparently "hot" wires in the panel will confirm 240-volt service. If only one cable is "hot" (testing cable to ground) it is a 120 V system. If both cables are "hot" to ground but there is no voltage between them it is a 120V system which has been "split" to look like 240V but it is not 240V.
What's the difference between using a neon tester (shown at left) and using a VOM or digital voltage meter?
A neon tester, containing just a light bulb, simply indicates the presence of live voltage but not the actual voltage level. A volt meter is required to test for other voltage levels or to determine the actual voltage level as well as to check for voltage that may vary over time.
Safety Warning: The ASHI Standards of Practice and other home inspection standards for electrical inspections do not require the inspector to insert any instrument into the service panel.
Therefore this testing is optional. It's also a dangerous procedure that can damage electrical equipment or worse, cause electrical shock, or even death, and should not be undertaken unless the person conducting the examination is trained and competent to avoid electric shock.
If the inspector is not trained for this procedure
s/he should never insert any instrument or tool into electrical equipment. See SAFETY for ELECTRICAL INSPECTORS at Residential Electric Panels.
In this article we provide photographs and descriptions of each of these types of electrical test instruments. At DMM Digital Multimeter HOW TO USE we explain the function and level settings and probe connections needed when using a VOM or DMM to measure voltage (as well as when measuring current or resistance).
Photographs & properties of electrical test equipment useful for a building inspector, electrical inspector, contractor, or homeowner
If you're unsure about the definitions of amps, volts, ohms, resistance, watts, etc. See DEFINITIONS of ELECTRICAL TERMS.
A voltage detector of voltage sensor detects the presence of live AC voltage (some equipment also detects DC voltage), with a sensitivity typically between 5 and 1000 Volts. This equipment can sense the presence of live electrical devices or wiring without touching the device or wire.
Shown here (left) is the Greenlee® GT-16 adjustable voltage detector. Greenlee and other manufacturers recommend that you test the operation of the voltage detector on a known live circuit both before and after using it to test for the presence of electrical voltage at a wire or device.
This device uses an AAA battery and has a sensitivity adjustment (the yellow dial in the center of the green patch on the device).
Some voltage sensors such as the FCB Voltage Pen operate without requiring a battery.
Tic Tracer Tif 300cc voltage detector - properties & special uses: A different sort of voltage sensor detects the presence of live AC voltage is shown at left, the Tif 300cc Tic Tracer.
Depending on the version, this instrument does not use an LED or neon bulb but emits a buzzing or "ticking" noise at a varying rate depending on how close it is held to a voltage source and also varying by voltage level.
Turning the instrument on gives a slow electronic tic-tic sound at a regular rate. Holding the sensor tip close to an electrical outlet or even along an electrical wire connected to such a receptacle results in an increase in the tic rate of the instrument.
And with even a limited amount of practice you can quickly learn to recognize the much faster tic rate (really a buzz) that the TIF makes when held close to a 240V circuit in comparison with a 120V electrical circuit.
Unlike the elegantly simple neon tester, and more like the Greenlee® GT-16, the TIF Tic Tracer does not need direct contact between sensor pins and live electrical contacts in order to detect the presence of electrical voltage (photo, above left).
But unlike the Greenlee® GT-16 that needs to be very close to an electrical circuit or component in order to indicate the presence of voltage, the TIF Tic Tracer 300cc can sometimes detect the presence of electrical wires behind drywall (depending on the depth of wires inside the wall cavity and other factors) - as we illustrate in our second Tif 300cc photo, shown at left.
Watch out: the sensor tip of the Tif Tic Tracer is also sensitive to static electricity and possibly to vibration.
If you rapidly swipe the sensor tip along the surface of a wall the instrument will sound wildly - an effect we once used to castigate an aggressive bystander.
Analog VOMs - Volt-Ohm-Milliameters
A VOM or volt-ohm meter may also be found in an analog form such as our favorite and now a collectors-item little Jensen VOM that we've used for nearly 30 years. Here our photo shows the Jensen analog VOM with its probes attached but not connected to anything.
In 30 years of use we needed one repair of this instrument - an internal fuse which we couldn't find locally. In analog VOMs such as this unit there is typically a very low-amperage fuse whose function is to protect the meter movement from damage.
On contacting Jensen Corporation, the company kindly sent us a few spare fuses. The total repair bill? $0.00.
This little VOM, ca 1985, is about 1/8 the size of the Simpson 260, ca 1958, described just below.
Simpson produces a wide range of test instruments including analog VOMs that can be used to measure resistance (ohms), direct current, alternating current, and even decibels.
Simpson Analog VOMs
Shown here is the Simpson Model 260 Series III Volt-Ohm Milliammeter produced ca 1958 and in use by its owner Paul Galow since ca 1959. This VOM is much larger than the compact devices in wide use today, having a meter display width of 4 1/2".
The device is also quite durable. Mr. Galow reports having to perform two maintenance chores on the instrument, replacing a battery and replacing a soldered-in-place fuse whose function is the protection of the meter movement.
Watch out: don't confuse a volt-ohm-milliameter with clamp-on ammeteres (described next). The Amps measurement range of this Simpson Model 250 VOM is 1MA to 500MA - not at all in the range of household appliances or larger equipment. For higher ampacity measurements you will need an ammeter such as the device described just below. See this circuit diagram of the Smipson 260.
Amperage or current measurements using clamp on or snap around digital ammeters, DMMs, & (some) VOMs
At left we are measuring the current draw in amps for the charging block of a laptop computer. Shown is Sperry's Digisnap DSA-500 snap-around digital multimeter.
Notice that the electrical wire was split so that the clamp-on ammeter's jaws surround just one of the two electrical wires. The transformer jaws or "clamp" must surround just one of the two 120V wires supplying the electrical device.
Also notice that we did not disturb nor damage the electrical wire insulation itself - doing so is dangerous and risks equipment damage or dangerous electrical shock as we cite just above.
At the moment of our measurement this electrical device was drawing 0.29A at 120V.
For an accurate calculation of actual energy consumed that includes the effects of AC current and power factors, see Definition of Power Factor, Real Power.
What about using a simple receptacle tester to measure voltage?
Receptacle testers are used by most home inspectors to check for proper wiring at electrical receptacles as well as to check the function of GFCI's.
For testing AFCI's the only reliable test currently available is the device's own test button. We provide details about using receptacle testers at Electrical Tools Every Homeowner Should Have
Where to Buy a DMM or VOM
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