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I'm trying to figure out what the proper burden resistor I should use, but the information I'm reading from OpenEnergyMonitor answer for the proper resistor values doesn't match what I was expecting.

So I'm using YHDC SCT013-000, which has a rating of:

  • 100A Max current
  • 50mA rated output
  • 1:2000 turns ratio

I'm looking for a burden resistor that gives me a 3.3 output. So my thought process was to calculate the needed resistor with Ohm's Law.

  • 50mA / 3.3V = 66 Ohms

Now on openEnergyMOnitor.org they multiple the output from the clamp by 1.414 (squareRoot(2)). To turn the output rating from RMS to peak to peak. Which if I do that it will reduce my burden resistor down to like 47 ohms.

My question is does that make sense. Are CT transformers usually in RMS vs peak to peak voltage.

current test I've tried the original burden resistor I suggested and it seemed to work at the lower ranges that I was testing. Just don't know if it will fail if the current goes higher I guess. Also curious to understand why there suggesting the conversion.

openEnergyMonitor.org example - https://docs.openenergymonitor.org/electricity-monitoring/ct-sensors/interface-with-arduino.html

DataSheet for clamp https://en.yhdc.com/comp/file/download.do?id=941

Notes - the openEnergyMonitor is geared towards an Arduino, which only has 0-5V range. While I'm using a external ADC that has a -3.3 to 3.3 range.

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  • \$\begingroup\$ What burden resistor is suggested by the CT data sheet? \$\endgroup\$
    – Andy aka
    Commented Dec 29, 2022 at 0:38
  • \$\begingroup\$ "... they multiple the output from the clamp by 1.414 (squareRoot(2)). To turn the output rating from RMS to peak to peak." Not quite. \$ V_{peak} = \sqrt 2 V_{rms} \$. i.e. The voltage from 0 to peak - not peak to peak. \$ V_{p-p} = 2 \sqrt 2 V_{rms} \$. \$\endgroup\$
    – Transistor
    Commented Dec 29, 2022 at 1:06

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The current ratio applies to both RMS and peak-to-peak currents, but for measurement with an ADC you need to consider the peak-to-peak at the highest current you need to measure. In my experience, and confirmed by experiment, the burden resistor can be quite a bit smaller as well as somewhat larger than recommended, depending on your needs. So for 100A RMS the output will be 50 mA RMS or 71 mA P-P. To get +/- 3.3V for your ADC, the burden resistor should be 47 ohms.

I assume your ADC communicates with the Arduino via I2C or SPI, so you don't need to worry about adjusting for the 5V range of the Arduino. Otherwise you need to use a voltage divider to the 5V reference as explained in the article.

The data sheet shows acceptable burden resistors from 10 ohms to 500 ohms, so 47 ohms is perfect.

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