From the website the SCT-013-050 outputs 0 to 1 volt for a current of 0 to 50 amps. I agree the "burden" resistor is built in on this module. Please verify you are only passing one of the coffeemaker wires through the sensor. If you pass the whole cable through the sensor you will get no output voltage from the sensor. A typical coffee maker requires ~1000 watts. At 230 vac this is ~4 amps. So the output of the current sensor should be about +/- 4/50*1 = 0.08 volts. This means the arduino has to measure readings from 0 to about 0.11 volts then calculate the RMS. doable but the readings are getting somewhat small to be stable. I would suggest: measure the sensor output with a multimeter if you have one. Change the reference of A/D converter on the Arduino from the default to the 1.1V internal reference. Not sure the code but you should be able to find it easy enough. you can increase the output of the sensor by passing the coffee maker wire through multiple times. For each time the wire goes through the sensor the sensitivity is increased by that number. for example if you pass the wire through the sensor 3 times. The output becomes 0 to 1 volt for 0 to 50/3 amps . Add a 0.1µF Capacitor across the sensor (where the burden resistor is shown on your diagram. This will remove some of the noise that exists on all AC lines.