Measuring AC current with an Arduino can be a little tricky.  The use of this Itead TA12-100 current transformer makes it possible.

Current sensor ICs allow design engineers to use Hall-effect-based current

sensor ICs in new applications where increased energy efficiency or new operating

features are required.

Specifications

• Onboard precision micro current transformer.
• Onboard sampling resistor .
•  Module can be measured within 5 a alternating current, the corresponding analog output 5 A/ 5 mA
•  PCB board size: 18.3 (mm) x17 (mm).
•  Rated Primary Current at 50/60 Hz: 5 A
•  Maximum Primary Current at 50/60 Hz: 20 A
•  Turns Ratio: Np:Ns = 1:2,500
•  Current Ratio: 5A:2mA
•  Winding D.C. Resistance at 20 °C: 155 Ω
•  Accuracy •@RL≤10 Ω: 2%
•  Operating Temperature: -40 to 85 °C
• Storage Temperature: -45 to 90 °C
• Dielectric Withstanding Voltage: 4,000 V / 1 mA / 1 sec