Do I need to install an FCU?
Posted: Sun Oct 03, 2021 3:02 pm
Back to basic idea of the ring final, it was designed to save materials needed for the rebuild after WW2, the orignal used imperial sized cable which would be around 2.9 mm sq, so slightly heavier than used today, and the pins were solid brass not sleeved so transmitted the heat away from the fuse a little better. But not much changed since 1947.
The idea is 20 amp rated cable can be used for a 32 amp supply. But to ensure no overload don't want heavy loads at the ends, centre OK as even shared.
We consider three wires in a termial OK, but four it is possible one is not clamped well, so only one spur from a socket on the ring so only three wires.
The spur with 2.5 mm cable could be overloaded if more than one socket, so either a fuse or no more than one socket, for some reason a double socket is permitted, but not two singles.
Radials use heavier cable 4 mm sq or smaller overload 20 amp.
We were told when inspecting and testing to check to see no figure of 8, not really sure why, can't find any rule to stop of fig 8, but due to the smaller cable used today the rule of thumb is any fixed appliance over 2 kW should have a dedicated circuit.
We have done this with the immersion heater, but it would also include any appliance which used over 2 kW for an extended time like a tumble dryer should also be on a dedicated circuit, but we tend not to.
So the rules allow for people doing things like plugging in a tumble dryer, so the 13A fuse should blow if a tumble dryer and washing machine are on the same fused spur, not sure it would, but that was the idea.
The idea is 20 amp rated cable can be used for a 32 amp supply. But to ensure no overload don't want heavy loads at the ends, centre OK as even shared.
We consider three wires in a termial OK, but four it is possible one is not clamped well, so only one spur from a socket on the ring so only three wires.
The spur with 2.5 mm cable could be overloaded if more than one socket, so either a fuse or no more than one socket, for some reason a double socket is permitted, but not two singles.
Radials use heavier cable 4 mm sq or smaller overload 20 amp.
We were told when inspecting and testing to check to see no figure of 8, not really sure why, can't find any rule to stop of fig 8, but due to the smaller cable used today the rule of thumb is any fixed appliance over 2 kW should have a dedicated circuit.
We have done this with the immersion heater, but it would also include any appliance which used over 2 kW for an extended time like a tumble dryer should also be on a dedicated circuit, but we tend not to.
So the rules allow for people doing things like plugging in a tumble dryer, so the 13A fuse should blow if a tumble dryer and washing machine are on the same fused spur, not sure it would, but that was the idea.