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You can measure AC current without cutting a wire by clamping a split-core current transformer (CT) around one conductor, then reading its low-voltage signal through an I2C metering circuit. For a ready-made option, SparkFun’s ADE7953 Qwiic board accepts a CT and communicates over I2C; its voltage channel is not exposed, however, so the board measures AC current rather than true watts. SparkFun’s kit bundles the board with a 100 A-to-50 mA CT.
What a non-contact I2C meter can measure
A split-core CT senses the magnetic field produced by current in a conductor. The clamp closes around the conductor without making an electrical connection to it, and its low-voltage output feeds a metering IC or an ADC. The resulting readings can be made available to a host over I2C.
“Power meter” can mean different things here. Current alone is not enough to determine true AC power when voltage or power factor varies. True active power requires voltage and current information, including their relationship over the AC cycle. A current-only board can monitor current, but it cannot directly report true watts just because its metering IC supports power calculations.
Which I2C options fit the job?
| Option | What it measures and how it connects | CT included? | Published performance or limits |
|---|---|---|---|
| SparkFun ADE7953 Qwiic board | Two current channels via a CT input through a 3.5 mm jack; I2C by default. The ADE7953 voltage channel is not exposed on this breakout, so it is an AC-current monitor. | No; an external compatible clamp is required. | SparkFun specifies less than 0.2% instantaneous IRMS error over a 1000:1 dynamic range for its kit documentation. This is a product specification, not a guarantee for every CT, installation, or complete measurement setup. |
| SparkFun Non-Invasive Current Sensor Kit | The same Qwiic ADE7953 board, intended as a solderless I2C setup, with current sensing through the CT. | Yes: a 100 A-to-50 mA split-core CT. | SparkFun specifies less than 0.2% instantaneous IRMS error over a 1000:1 dynamic range. The stated CT rating is 100 A to 50 mA; it does not by itself establish accuracy across every operating condition. |
| MikroElektronika AC Current 2 Click | A non-contact, galvanically isolated clamp probe, MCP607 amplification, and MCP3221 ADC provide a digital I2C output for AC-current measurement. | The cited product description does not state whether the clamp is included. | Accuracy and dynamic range are not stated in the cited product description. |
| Custom metering PCB | ADE7953 or ADE9153A are options for CT-based metrology; STPMS2 and STPM32 are alternative metering IC families supporting CTs and other sensors. The host interface depends on the selected IC and board design. | Not stated; it depends on the design. | Board-level performance is not stated; it depends on the IC, analog design, CT, calibration, and implementation. |
Can the ADE7953 clamp board measure watts?
The ADE7953 IC is a single-phase metering IC with I2C access and support for RMS, active, reactive, and apparent measurements. Analog Devices specifies less than 0.1% active/reactive energy error over a 3000:1 dynamic range for the IC. That chip-level capability does not mean every board built around it exposes every measurement channel.
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#1 Best Overall
20A 125V AC Power Meter, NEMA 5-15P to 5-20R Outlet Monitor
- High-precision Power Measurement: Advanced sensing technology ensures accurate measurement of key power parameters such as current and voltage with minimal error, providing users with reliable energy usage data
- Comprehensive Power Monitoring: Not only can it measure basic power parameters, but it can also deeply analyze power quality, such as identifying interference factors such as voltage fluctuations, sags, swells, and transients
- Data Recording: Built-in large-capacity storage automatically records long-term historical power consumption data, supports backtracking at any time, and easily identifies power consumption patterns and trends through data analysis functions
- User-friendly Interface: Equipped with an easy-to-read display, all important information is clear at a glance. Easily restore factory settings, just long press the black button on the right side of the test meter for 5s to restore all data to the factory state, easy to maintain
- Widely Applicable: Adopts NEMA 5-15P to NEMA 5-20R standard interface, equipped with 20A circuit breaker. Suitable for connecting a wide range of electrical equipment in residential, commercial, educational and industrial environments
On SparkFun’s Qwiic breakout, the voltage channel is not exposed. The clamp board therefore provides current readings, not the voltage-and-current data needed to calculate true active watts for a load whose voltage or power factor may vary. To measure watts, use a design that also measures voltage through an appropriate isolated voltage-sensing channel, or select a complete energy-metering design that provides both voltage and current measurements. Do not treat a current-only reading as a true-power reading.
Quick Recap
Bestseller No. 1
Bestseller No. 4
Best Value
HiLetgo Digital Multimeter AC 80-260V 100A PZEM-061 LCD Display Digital Current Voltage Power Energy Multimeter Ammeter Voltmeter with Current Transformer CT
- The meter can only measure the active power(real power). It doesn't show Apparent power. If you measure power from a DC-AC inverter please make sure it's PURE SINE WAVE. Otherwise the meter can be burnt or melted.
- Voltage test range: One-Phase 80~260V AC Power, 50/60HZ; Current test range: 0~100A; Inner diameter of the CT: 15mm/0.6''.
- Overload alarm function (over power alarm threshold, backlight and power flickering prompt).
- The backlight can be turned on or off by pressing the button briefly, and the backlight status is automatically saved after power-off; Store energy data when power off(can be reset).
- Great display (display voltage, current, active power, energy at the same time), easy to install, 2 wires for the ct clamp and 2 wires for the line 1 and line 2 voltage reading, checked voltage and amperage against a Fieldpiece meter and read spot on, can easily make a rectangular in drywall 1 13/16 x 3 5/16 in to recess the display nicely.
Rank #4
20A AC Power Meter, NEMA 5-15P to 5-20R Outlet Monitor
- High-precision Monitor: AC power meter uses a sensitive electromagnetic coil, which can accurately monitor voltage, current, power, frequency, power factor and other data in real time. Product parameters: Voltage: 0-125VAC, current: 0-20A AC, power consumption: 0-9000W, frequency: 45-65HZ, power factor: 0.00-1.00PF, power consumption: 0-99999kwh
- Electricity Safety: Equipped with short-circuit protection and overload protection. Some aging electrical equipment may have problems such as aging faults, over-power, over-rated voltage, etc. Equip these equipment with monitors to detect problem data in a timely manner and reduce risks
- Widely Used: NEMA 5-15P to NEMA 5-15R Ground Fault Protected Outlets, mainly used in residential sockets (such as lights, chargers and small kitchen appliances), commercial spaces (computers, printers, lighting and other electronics equipment power supply), educational equipment (power supply for projectors, computers and other classroom equipment), industrial equipment electrical appliances with a current of 15A
- Accurate Billing: Accurate measurement of energy consumption is critical for billing in both domestic and commercial. Power meters are used to monitor the power usage of various electrical equipment, appliances, or entire electrical systems, providing a reliable method to measure actual energy usage of individual devices or parts of a facility
- Plug and Play: No electrical installation required! Just plug it in and get safe, fast power usage and power monitoring for your home. 6.56ft 12AWG cable makes it easier for users to place the power monitor in a more flexible location for viewing
Rank #3
Sale
AC 80-260V 100A Digital Power Monitor, LCD, Split-Core CT, 2-Pack
- 1.Digital Multimeter:This power energy meter can measure and display voltage current active power energy frequency and power factor at the same time.with split current transformer,more convenient to install
- 2.Overload Alarm function:Backlight and power will flash simultaneously to give an alarm when exceeding the preset value.You can preset power limit by yourself
- 3.Automatic Data Storage Function:The last test data is stored automatically when the power supply abruptly lose. Don't worry about data loss due to sudden power outages
- 4.One-touch Control:The button can be used to control the backlight,reset energy, preset power alarm limit
- 5.LCD Display:Large-screen LCD with all sight 180° view,The blue backlight can be turned on/off manually. PZEM-022 requires an external power supply to light up the screen
Rank #2
Sale
AC 80-260V 100A Hardwired Power Meter, LCD, Split-Core, Energy Monitor
- 1. Monitors key AC power readings in one panel display: This hardwired AC power meter shows voltage, current, wattage, kWh energy, frequency and power factor, helping you watch generator load, RV power, workshop circuits or appliance consumption in real time
- 2. Split-core CT makes installation easier: The included 100A current transformer clamps around one live conductor, so you do not need to cut the monitored wire; for 120/240V split-phase systems, monitor one leg per meter or use separate meters as needed
- 3. Wide AC range for common electrical panels: Designed for 80-260VAC circuits with 0-100A current measurement and up to 22,000W rated power, this meter is useful for household, garage, generator, RV and light commercial monitoring projects
- 4. Power-off memory and visual overload alarm: The meter can store energy data and settings after power loss, and the backlight/power display flashes when the preset power threshold is exceeded, giving a clear visual warning for load monitoring
- 5. Clear LCD display for practical troubleshooting: The compact panel meter provides quick readings for energy use and load balancing, with 1.0 grade monitoring accuracy; it is intended for hardwired installation and should be installed with proper electrical safety precautions
How to set up a CT for an I2C current reading
- Choose the sensor and board together. Confirm the CT type, current rating, output ratio, connector, and board input requirements. The SparkFun kit supplies a 100 A-to-50 mA CT with its ADE7953 Qwiic board; the board-only version requires an external clamp.
- Clamp around one conductor only. Put the CT around the line or neutral conductor, not around a cable containing both. When line and neutral pass together through the CT, their opposing magnetic fields largely cancel, yielding little net signal.
- Connect the CT output to the metering input. For the SparkFun board, the clamp connects through its 3.5 mm jack. Follow the board and CT manufacturer’s wiring and installation instructions rather than assuming another CT is interchangeable.
- Connect the host over I2C. The SparkFun board uses I2C by default; read the metering data made available by the board using its supported host setup. The AC Current 2 Click also provides I2C output, but uses its own clamp, amplification, and ADC arrangement.
- Interpret readings according to the channels actually present. A current-only board reports current-related measurements. Use voltage and current sensing together when the desired result is true watts, energy, or power factor.
Safety and accuracy limits to account for
- Isolation is not permission to handle exposed mains wiring. The CT sensing path is non-contact, but opening an enclosure or positioning a clamp near mains conductors can still expose hazardous voltage. Follow applicable electrical-safety practices and the CT and board manufacturers’ installation guidance.
- Respect the manufacturer’s insulation and construction requirements. In particular, follow guidance for insulation, burden, creepage, and enclosure design. These details matter especially when designing a custom mains-measurement PCB.
- Match the CT to the input and use case. The rating and output ratio affect the signal delivered to the meter. Do not assume a CT’s headline current rating alone establishes the board’s usable range or accuracy.
- Read accuracy figures in context. Analog Devices’ less-than-0.1% figure describes active/reactive energy error over a 3000:1 dynamic range for the ADE7953 product specification. SparkFun’s less-than-0.2% figure describes instantaneous IRMS error over a 1000:1 dynamic range in its kit specification. The quantities and ranges differ, and neither figure is an independent guarantee for a whole installation.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
