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ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
AFCIs ARC FAULT CIRCUIT INTERRUPTERS
ALUMINUM WIRING HAZARDS & REPAIRS
AMPS VOLTS DETERMINATION
APPLIANCE EFFICIENCY RATINGS
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 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
WIND TURBINES & LIGHTNING
ZINSCO SYLVANIA ELECTRICAL PANELS
How to measure electricity usage & measure electrical current or amps - the current drawn by an electrical circuit, device, or appliance. Measuring the current drawn by an electrical device such as an air conditioner compressor motor, electrical motor, or an electrical circuit in a building can give useful diagnostic information and can also give insight into which electrical circuits or appliances are the heavy users of electricity. This article describes using the Digisnap DSA-500 snap-around digital multimeter from A.W. Sperry Instruments to measure the amps drawn by a simple electrical circuit, device, or appliance. For details about connecting probes and setting function and level switches on VOMs and DMMs, see DMM Digital Multimeter, How to Use. For measuring volts or voltage levels, see VOLTS / AMPS MEASUREMENT EQUIP. Also see USING DMMs VOMs SAFELY as well as SAFETY for ELECTRICAL INSPECTORS.
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What's the Difference between Determining Service Ampacity and Measuring Amps at an Electrical Service, Circuit, Appliance or Device?
In this article we describe various methods for actually measuring the amps or electricity usage at a building, circuit, or device. But first, let's not confuse the determination of the ampacity of an electrical service at a building with amps measurement at a building, electrical circuit, or device.
What's the difference between determining the ampacity of the electrical service at a building and making actual amps measurements at an electrical service, circuit, or electrical device?
Making an amps measurement on a building circuit or at an appliance, motor, or air conditioner etc.
Measuring electrical amps is the measurement of current draw or amps or amount of electricity being consumed is an actual instantaneous measurement of actual electrical power use at the moment, not a measurement of the design capacity or capability of the electrical service at a building or in an electrical circuit.
The actual current draw or total amps being consumed on an individual electrical circuit in a residential building should (with minor technical exceptions) be a number below the ampacity of the circuit breaker or fuse protecting that circuit - typically 15Amps, 20Amps, or for some appliances a larger number, e.g. 30A or 40A at an electric water heater and at some central air conditioner/heat pump systems.
Of course if no electrical devices or appliances are turned "on" at an individual electrical circuit, the amps or current draw measured there should be zero.
Determining the total electrical service ampacity for a building
Ampacity ratings describe the safe capacity of an electrical system, circuit, or device, not the actual amount of electrical energy that that system, circuit, or device may happen to be carrying or using at a particular moment. For example, a #14 gauge copper electrical wire is typically rated to safely conduct 15 Amps (15A) of electrical current while a #12 copper wire is rated to safely conduct 20A of electrical current.
Determining the electrical service ampacity means answering the question "how much total electrical power or current can a building's electrical system safely use at one time?" We discuss this procedure in detail beginning at AMPS VOLTS DETERMINATION . Practically, the total capacity of an electrical system, measured in amps, sets the limit on how many electrical devices (lights, refrigerators, air conditioners) can be run simultaneously without overloading the system. Overloading an electrical system or overloading an individual electrical circuit should trip a circuit breaker or blow a fuse. If those safety devices are subverted, not properly installed, are defective, or malfunction, the risk is that an overheated wire or connector or device ignites a building fire.
The service ampacity at an individual residential building typically will be somewhere between 60Amps (below current minimum standards for a home in the U.S. or Canada) and 200Amps.
We define Amps, Volts, and other electrical terms in more detail at Electrical Definitions.
When we make an amps measurement at a building we are determining the current draw for all of the electrical devices that are in operation at that moment. We are seeing the rate of electricity usage.
Only by including the length of time that a building, circuit, or device is using electricity at a given rate (and voltage) can we know the total electricity used. That's the job of electrical meters. Typically we express electrical usage rates in watts, where Watts = Volts x Amps.
See Definition of Watts and also Definition of Power Factor, Real Power for examples of actual calculations of electrical energy usage that combines volts, amps, and other terms in order to accurately describe the electricity or energy used by a light bulb, an air conditioner, or other electrical circuits or devices.
In our page top photo and in our photos below you can see Sperry's Digisnap DSA-500 snap-around digital multimeter in use measuring the amperage level on a 120V electrical circuit fed into a building from the electric meter.
The jaws of the DMM-ammeter are closed around one 120-V service entry wire in its routing between the electric meter's output lug and the electrical panel's main input connecting lug (not shown in this photo). In the U.S. and Canada it would usually be necessary to open the electric meter enclosure to access these wires. You can see that at the moment of measurement, this 120V circuit was drawing only 1.35A. Inside we observed that the only operating devices on this circuit were some electric lights and computer equipment.
Procedure for Measuring the Amps or Current Draw by an Individual Electrical Appliance, Device, Motor, etc.
Frequently Asked Questions (FAQs) about measuring building or circuit or device amps or electrical current draw
Questions & answers or comments about measuring amps or current used by an entire building or by an individual electrical circuit, appliance, motor, or device - Digisnap DSA-500 snap-around digital multimeter from A.W. Sperry - photos, use, advice.
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