Can I measure the level DC 'leakage' current piggy backing on an AC supply?

[spud1]

Hi !

Much talk of the use of type A, type B and Type F RCDs recently.
As we know all are specified at varying levels to ignore the blinding effects of transient DC currents, that are being superimposed on our AC circuits by modern technology.

But is there a means to measure the level of this superimposed DC current ?

We are told that 6mA of leakage current is the arbitrary cutoff between using a type A and a Type B or F RCD, but how do we determine when that 6mA has been reached?

Is there a clamp meter for example that can read sufficiently low enough DC current amongst the noise of the AC supply? I know that Megger do an 'earth leakage clamp meter' (DCM305e) but this is only for measuring AC leakage on the CPC.

Presumably the DC transient currents we are talking about are on the line and neutral conductors.

Thanks in advance.

 

[pc1966]

The main difference between type A and type B is the B will trip on smooth DC, the sort you would get from a battery or similar, where as type A only works on "pulsed DC" (sort you get from rectified AC), a combination of DC and AC, as they have a differential transformer that is not so easily saturated by the DC part but actually trip on the AC component of that waveform.

You can get DC clamp meters but they are expensive, same reason type B RCDs are expensive I guess! Here is an example:

CP 41 | GMC-I Prosys CP41 Clamp Meter, 40A dc, Max Current 40A ac CAT III 300V | RS

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