This is a Non-Invasive AC Current Sensor Clamp, also know as a CT Clamp. It is the genuine YHDC brand. The SCT-013 is available in a couple of different versions. This version(SCT-013-000) is the most common one used, and will output 0 to 50mA when the measured wire is conducting 0 to 100A. It does NOT have an internal resistor. Normally it will be connected to a resistor on the target board that will convert the current (0-50mA) to a voltage. Current transformers (CTs) are sensors that are used for measuring alternating current. They are particularly useful for measuring whole building electricity consumption (or generation for that matter). The split core is particularly suitable for DIY use it can be clipped straight on to either the live or neutral wire coming into the building without having to do any high voltage electrical work. Common applications include current measurement, monitoring and protection of AC motor, lighting equipment, air compressor, etc.  Note: Colour might change due to different batches. Use with OpenEnergyMonitor: For information on how to use this sensor with OpenEnergyMonitor, click here.see this page: learn.openenergymonitor.org/electricity-monitoring/ct-sensors/yhdc-sct-013-000-ct-sensor-report Use with IoTaWatt This CT can be used with IoTaWatt. In IoTaWatt CT configuration, select SCT013. For details click here.see this page: docs.iotawatt.com/en/master/CTconfig.html#configuring-the-input-channels Features Model: SCT-013-000 Frequency Range: 50HZ-1KHZ Rated input Current: 100A Maximum input Current: 120A Core material: ferrite Opening size: 13mm * 13mm Linearity: < 0.2% Lead length: 1 meter Connector: Standard Φ3.5 three pin plug output ,current, voltage, two kinds of output forms (voltage output, built-in sampling resistor) Mechanical strength: opening and closing times not less than 1000 times (test at 20 degrees Celsius) Safety indicators: resistance to electrical strength (shell and output)6000V AC/1min flame retardant properties conform to UL94-V0 Weight: 50g Working temperature: -25 ~ 70 Package Includes 1 x SCT-013-000 Current Sensor [mx_insert-post-ebay slug="ebay-t-default"] SKU: SEN0-000 Category: Current & Power Sensors