The table below is from this document: Schneider RCD

When the maximum response of the device is 40 mS, does it measure current doing RMS or peak detection? The document does not explicitly say it. However, in general, RCDs should trip quick (below 50 ms) when protecting humans.

My question is: Is a time below 50 ms enough to perform RMS and trip the device? Let's say that we have a digital RCD that uses a microcontroller and ADC. I think the only way to trip that fast is comparing instantaneous values to a threshold. But what if the signal is noisy and deciding based on inst values cause nuisance tripping? In this case RMS would be a better measure at the expense of being slower. So my second question: In 40 ms I have 2 cycles of 50 Hz and like 2.4 cycles of 60Hz. In this case the RMS measurement for the 60 Hz would not be accurate because sampling time is not an integer number of cycles, right?

enter image description here

  • $\begingroup$ hi! This sounds very much like a candidate for the electronics.Stackexchange.com site, not like a signal processing question. I see how sampling brings this into a DSP-adjacent domain (and hence, I think it's on-topic here), but honestly, I can't tell you much about the reasons and how such tripping tresholds are specified – and that might be very important to how you'd want to implement them digitally. $\endgroup$ – Marcus Müller Oct 24 '20 at 7:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.