Method for checking the adequacy at the residual currents of differential circuit breakers

1 . A method for checking adequacy at residual currents passing through a differential circuit breaker disposed at a head of an electrical installation, by means of a leakage current measuring clamp gripping active conductors exiting the differential circuit breaker to power a plurality of electrical appliances, the method comprising in:

acquiring over a total acquisition duration (t end -t dstart ), at a determined sampling frequency, residual current samples during successive acquisition periods,

frequency-analyzing by fast Fourier transform (FFT) the residual current samples in predetermined frequency bands,

determining for each frequency band of each acquisition period, a maximum effective current and, at an end of the total acquisition duration, recording a maximum value of maximum effective currents determined in each band frequency, and

disqualifying or not the differential circuit breaker depending on whether or not this maximum value of the maximum effective currents meets a predetermined compatibility condition and displaying this disqualification or non-disqualification in binary mode by a pictogram on the leakage current measuring clamp.

2 . The method according to claim 1 , wherein the predetermined frequency bands are the following four: DC; DC-50 Hz; 60 Hz-1 kHz; and 1 kHz-10 kHz.

3 . The method according to claim 2 , wherein calculation of the FFT is reduced by determining it only up to 1 kHz, the frequency band 1 kHz-10 kHz being calculated by quadratic subtraction between a total effective current obtained over an entire frequency range of DC-10 kHz and a sum of the residual current samples obtained in the frequency band DC-1 kHz.

4 . The method according to claim 3 , wherein the calculation of the FFT is preceded by a Hanning or Hamming windowing applied to a determined number of residual current samples.

5 . The method according to claim 1 , wherein use of a differential circuit breaker of the AC, A, or F type which is not recommended is displayed on the leakage current measuring clamp respectively by at least one of the following pictograms:

a crossed-out AC pictogram;

a crossed-out A pictogram; and

a crossed-out F pictogram.

6 . The method according to claim 4 , wherein the maximum current value in each of the frequency bands defining the predetermined compatibility condition and leading to the disqualification of the differential circuit breaker is given by the following table:

Displayed

DC

DC-50 Hz

60 Hz-1 kHz

>1 kHz

pictograms

>1 mA

any

any

any

a crossed-out

and

AC pictogram

<6 mA

any

crossed-out

AC and A

≥6 mA

any

any

pictograms

and

<10 mA

≥10 mA

any

any

any

crossed-out

AC, A, and F

pictograms

any

>1 mA

any

any

crossed-out

AC and A

pictograms

any

any

>1 mA

any

crossed-out

≤IΔn

AC and A

pictograms

any

any

>IΔn

any

crossed-out

AC, A, and F

pictograms.

7 . The method according to claim 3 , wherein the total effective current is calculated by simple quadratic addition of all the residual current samples.

8 . The method according to claim 1 , wherein DC current is calculated by averaging the residual current samples.

9 . The method according to claim 1 , wherein each of the successive acquisition periods has a fixed duration of 100 ms, the sampling frequency is 81 . 92 kHz and a determined number of samples for calculation of the FFT is 512.

10 . A leakage current measuring clamp including an AC+DC current sensor able to measure AC or DC currents from 1 mA, over a frequency band comprised between O Hz and 10 kHz minimum, and a processing module specially configured to implement the method according to claim 1 .