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I have RCCB/RCD with four circuit breakers at the entrance of my aparment (I am actually not quite sure how it is called in english, so here is RCCD and CB is ABB s231r with different max amps)

Recently, I've been setting up electrical socket in the kitchen, so I turned off cb, that handling kitchen line and installed socket. During this process from time to time I've been double checking on line voltage (with N and with PE) with multimeter (just in case) and couple of times during this process my RCCB triggered. What can cause this behaviour? As I know, RCCB only triggers when there are differential current in the circuit, so if every properly working circuit have some small amount of differential current by design, if I disable one of the lines with CB this differential current should decrease?

  • What make and model of meter are you using for this test? – ThreePhaseEel May 21 at 23:04
  • @ThreePhaseEel Mastech MAS838 – IgorNikolaev May 21 at 23:07
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An RCD (in any form) is always looking at the current going out vs the current coming back, which SHOULD be zero difference, so if they are different by the amount of your RCD (usually 10 to 30mA in your part of the world), the device trips. It might be that your type of meter is one that measures by looking at the potential difference by putting on a small load, so the act of trying to read voltages was a condition that the RCD interpreted as a short.

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  • this totally makes sense for me. but the line, that was inspected was cut off by cb in the first place. So may be question should be rephrased as "how cuting off one of the cbs, could affect another lines in "increasing differential current" manner?. I am actually just inspected voltage on the socket bot L with N and L with PE and RCD didn't trigger – IgorNikolaev May 21 at 20:27
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Most circuit breakers only disconnect hot/phase. They do not disconnect neutral.

The problem is, somewhere in your handling of the wires, you managed to touch neutral to safety earth. Now, the electricity returning on neutralfrom other circuits has two paths: It can go back the normal way through the RCCB, or it can go via this circuit's neutral, to the safety earth wire, to the panel, and to the neutral-earth equipotential bond on the far side of the RCCB.

It flows on both paths at once, in proportion to their conductance (1/resistance).

That diverted enough current flow to imbalance the RCCB and trip it.

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  • Yeah, the earth-to-neutral sensing in most GFCI/RCD devices relies on the presence of a slight load – ThreePhaseEel May 22 at 0:09
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Is your RCD 1P or 1P+N? The first only interrupts th live, the second both conductors. If it's 1P you may have a residual current on the neutral leacking to PE making it to trip. An easy fix could be replacing the RCD with a 2P model

Also are you on TT earthing or TN distribution? If you're on TT your breakers must be at least 1P+N because neutral is considered "active" conductor, if you're on TN(-S) a connected neutral isn't that big issue.

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