Yes they are. Current alternates direction, but power usually only flows in one direction, from the input terminal (from the bus bar) to the output terminal (that the circuit is wired into).
replyIf the circuit will be supplying power too (e.g. battery storage, an EV and EVSE that supports powering the house from the EV, etc) then you need a bidirectional RCBO.
People with no differential fault protection need not worry about any of this, they'll just be killed when it goes badly wrong.
Source: Am a UK electrician
Example: https://assets.cef.co.uk/downloads/pdg/wylex_nhxs1b32_datash...
EDIT: To say nothing of people with unidirectional electricity meters; plugging these into those setups will get them prosecuted for electricity theft. All SMETS 2 smart meters are bidirectional; you'd best check your meter if it isn't one of those.
https://www.bgelectrical.uk/uk/circuit-protection/devices/rc...
Right there, both bidirectional and unidirectional breakers.
replyIt would be really interesting to know what's so special about these UK units that they can be "damaged" by being fed from the "wrong" side (as per some other article), considering that the only place where these behave like that is an island north of France.
replyNot in the US, but in parts of Europe they effectively use AFCI/GFCI breakers for everything.
replyThose are code in the us now too. (with exceptions for where they don't make sense)
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