Consumer unit / breaker panel

Frequently asked questions

Is an RCD the same as a GFCI?

Close in purpose and different in threshold and in where it sits. Both detect an imbalance between the current flowing out and the current returning — the signature of current leaking to earth, possibly through a person — and disconnect. British and Australian practice calls the device an RCD, commonly fits it at the consumer unit to protect groups of circuits or, increasingly, per circuit as an RCBO combining it with overcurrent protection. American practice calls it a GFCI, most familiarly built into a socket outlet in a wet location or into a breaker, and the trip threshold for personal protection differs from the RCD's typical figure. So the words map, the function maps, and the ratings and the installation conventions do not — which is why a device cannot simply be substituted across a specification.

What is an AFCI, and does Britain have one?

An arc-fault circuit interrupter detects the electrical signature of an arcing fault — a loose connection, a damaged cable, a pierced conductor — which can generate enough heat to start a fire while drawing too little current to trip an overcurrent device and causing no earth leakage for a residual-current device to see. It is a distinct protection from both, required in American practice for many circuit types. The British and European equivalent is the arc fault detection device, recognised in the wiring regulations and recommended rather than universally mandated. So the concept exists in both, under different names, with different scope — and a specification calling for AFCI protection is calling for a device that is not the default in a British consumer unit.

Why do the earthing arrangements differ so much?

Because the supply systems differ, and the protective arrangement follows from how the supply is earthed rather than from a preference. British practice classifies installations by earthing system — whether the earth comes with the supply cable, is combined with the neutral, or is provided by an electrode at the property — and the choice of protective device, the bonding of services and the acceptable earth loop impedance all follow from that classification. American and Canadian practice arranges the service grounding and bonding differently again, and Australian practice differently once more. The practical consequence is that the earthing section of a foreign specification cannot be read across even when every device name translates, because it is describing a different supply.