Strange MCB trip

[Ben Blaukopf]

RCD in the office trips. Colleague goes and unplugs the coffee machine (which is a reasonable suspect) and resets the RCD. The B32 MCB adjacent to it (which happens to control the circuit with the coffee machine in) trips. The RCD does not.

Reset the MCB, plug in the coffee machine again, and the RCD trips. Unplug coffee machine, reset RCD, all fine.

We reckon the pressure stat on the coffee machine has gone, which produces a (transient) earth leakage. But what tripped the MCB?

The only thing I can think of is inrush current on the fridge and freezer on that circuit and a bad alignment of the stars.

[Animal]

the only way to know is to test

[Brian Gaff]

Back when I worked we had similar issues, for whatever reason, turning off the mains and taking the sockets off the boxes and tightening all the screws fixed it and the problem never came back, so who knows. We never saw any fried spiders. Brian