Sitting here drinking my coffee about an hour ago, when 'click' the sockets power goes off.
There are 4 sockets circuits, 3 each have their own RCBO, one via a separate 100ma time delayed RCD. In a new CU installed about a year ago, no problems since then. TT earth.
All three RCBO's had switched off.
Turned them back on, and everything is fine, but left wondering why all
3 would go off like that together
Some RCDs/RCBOs also trip on other fault conditions, such as disconnected neutral (requires that the device has an earth tail connection). It may also be that some type of voltage spike triggered them, either on the supply, or in the ground where your rod is (will look like a disconnected neutral), due to someone else's earth fault or lightning strike.
Earth neutral short?
That's pretty-well all of the single-module solid-neutral types now. They trip if the voltage between the neutral and functional earth tails exceeds 50 volts (in practice about 42 volts for an MK branded one I tested recently).
Agreed. I'd expect the RCBOs to have some low-pass filtering to protect against tripping on 'spikes' (fast transients), so we're most likely looking at a 'surge' on the supply neutral. As you say a line-earth fault in the supply network or someone else's installation could lift the neutral enough to do this.
RCBOs work by monitoring the differential current between line and neutral.
If, anywhere within the installation, there is a neutral earth short, some current will be diverted to the earth path.
If that causes a big earth spike with respect to the neutral anything (and tehse dauys athats most electronics wit RFI filtering) that has an AC path between live, neutral an earth, will screw with the balance and cause things to trip.
As will a major sure on the live line.
Yes all types of RCD do that. Additionally the modern RCBOs also monitor the voltage between neutral and earth, and trip if it exceeds 50 V, or if the neutral goes o/c.
Yes, but that won't cause tripping of other final circuits. Here three final ccts tripped together. That's far more likely to be caused by a common fault, viz. something causing earth and neutral to move more then
50 V apart. Bearing in mind that this is a TT-earthed installation it's either something dumping current into the local earth electrode, or something remotely lifting the neutral. The latter seems more likely since local current diverted to earth should trip an RCD well before the rise in earth potential reaches 50 V.Those sorts of transients don't usually cause RCD tripping problems, unless the situation is already marginal with respect to leakage. And then they will only tend to affect a single circuit.
Ok, thanks folks, some external event then seems likely. shall file it away in list of odd things that have happened.
Though it didn't trip the 3 x lighting circuits or the boiler circuit RCBO's
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