FCU Placement

[otronics]

I have an FCU in my house that is a spur off a ring circuit.

There is about six meters of cable between the existing socket on the ring and the FCU.

Clearly an FCU should be at the beginning of the spur but does it actually matter that it's much further along?

[ericmark]

If one reads BS 7671 if there is no branch, one can fuse either end of a cable, as long as less than 3 meters.

433.2.2 The device protecting a conductor against overload may be installed along the run of that conductor if the part of the run between the point where a change occurs (in cross-sectional area, method of installation, type
of cable or conductor. or in environmental conditions) and the position of the protective device has neither branch circuits nor outlets for connection of current-using equipment and fulfils at least one of the following conditions:
(i) It is protected against fault current in accordance with the requirements stated in Section 434
(ii) Its length does not exceed 3 m, it is installed in such a manner as to reduce the risk of fault to a minimum, and it is installed in such a manner as to reduce to a minimum the risk of fire or danger to persons (see also Regulation 434.2.1).

However in real terms I have seen many an unfused spur over 3 meters, so I would not be unduly worried. An inspector would need to be rather pedantic to pick one up on being over 3 meters.

I found a socket I wanted to extend from was an unfused spur, so swapped it to a grid plate with a single socket, switch and fuse, use the LAP range from screwfix, could have used a twin socket box instead of double socket box, and used a FCU and socket, same result.

[otronics]

Thank you. Very useful.

[OnlyMe]

There is no logical reason why the FCU needs to be at the start of the spur.

[ericmark]

There is no logical reason why the FCU needs to be at the start of the spur.

I agree, I feel the 3-meter limit is aimed at items supplied from a bus bar system, not a ring final, but the regs don't stipulate that a ring final is a special case.

[OnlyMe]

(i) It is protected against fault current in accordance with the requirements stated in Section 434

is normally all that matters in a domestic property.