electtic shock - RCB did not trip

cutandshut

In my opinion there is a lot of mis-information here on the operation of an RCD. An RCD compares the current flowing from the line and back through the neutral. If there is a difference of more than 30ma (for a 30ma rated RCD) it will trip. This imbalance would be caused by a fault in a circuit causing a current in excess of 30ma to flow directly to earth rather than through the neutral. If one puts one's finger across the pins of a light fitting (kids don't try this at home) any current that flows, through ones finger, is from line to neutral not earth so no current imbalance is detected and the RCD will not trip. An RCD doesn't have an earth connection. A neutral to earth fault will always cause the RCD to trip irrespective of neutral voltage.

DVardysShadow

cutandshut wrote: »

In my opinion there is a lot of mis-information here on the operation of an RCD. An RCD compares the current flowing from the line and back through the neutral. If there is a difference of more than 30ma (for a 30ma rated RCD) it will trip. This imbalance would be caused by a fault in a circuit causing a current in excess of 30ma to flow directly to earth rather than through the neutral. If one puts one's finger across the pins of a light fitting (kids don't try this at home) any current that flows, through ones finger, is from line to neutral not earth so no current imbalance is detected and the RCD will not trip. An RCD doesn't have an earth connection. A neutral to earth fault will always cause the RCD to trip irrespective of neutral voltage.

I don't think there is any misinformation which has not been cleared up. Your description of how an RCD works is correct. However, if the neutral to earth voltage is low enough and the neutral earth loop impedance is too high, then you will not reach the threshold current to trip the RCD.