1. Why would you put a consumer unit on the end or is Taylor making a sarcastic joke?
Not sure.
I dont know what CCC stands for?
Current Carrying Capacity.
What I think you're saying is creating a spur with the 4mm wire instead of what Taylor would do which is use a 2.5mm wire and "fuse down" with a fuse that prevents more than 13.5 amp from crossing.
Well, 13 not 13.5 but yes, although a double socket is allowed so it could be 26A (CCC of 2.5mm² is 27A) yet a part of the regulations which shows
some examples of arrangements states that only one single socket is allowed. This obviously does not make sense.
Not sure how you achieve that without melting the fuse.
You don't; that is the protection.
Wouldn't a resistor be better?
No.
Please clarify "fuse down" as i'm just getting myself into a state of con'fuse'ion
The MCB in the CU is 32A so the circuit cables must have a CCC of at least 32A (2 x 2.5mm² as in the ring).
Using a cable with a CCC less than 32A (1 x 2.5mm²) relies on protection by the plug fuses - one or two - any more sockets/plugs requires separate protection of a lower than 27A fuse - fusing down - but 13A is the largest made for Fused Connection Units.
Or, of course, just use a cable with a CCC greater than 32A - 4mm².
2. I really dont get what Spark means by "Directly" and "ie not a spur" isnt the whole definition of a spur to directly connect to a circuit (in this case final ring) whether it be from the socket or by cutting the ring, wiring in a junction box and creating a spur off that?
I think he means what we are saying is alright connected to a socket on the ring (directly) and not to a socket that is already a spur on 2.5mm².
I understand what Taylor means by the max draw will be 26amps on the circuit at a double socket as the fuses within each consumer device are 13amps or less. Two consumer devices = 13 x 2. Ring finals are designed to accommodate this much current/amps even if only one "side" of the ring is connected to the socket/double socket. 2.5mm wire is rated up to 27amps
What i think Taylor is saying here is that if the 4mm wire draws just under 32amps then that would be bad. For the life of me I cant work out how the 4mm wire connected to a 2 gang socket would do this unless the device pulling from the socket is using a 35 amp fuse and is pulling 31.9amps. Even so, as as EFL said earlier the 2.5mm wires will distribute the load even if its over 26amps (for example the 4mm spur is pulling a 31.9amp load) if the spur is placed reasonably in the middle of the ring circuit.
Cables do not pull current. Appliances draw current and the cable has no say in the matter so need protecting.
In my mind the only potential issues I can see with doing this is if the ring circuit is massively extended, so the 4mm spur goes from being relatively in the middle to RELATIVELY too close to the CU. Which seems improbable to an ignorant bloke like me but i guess you could build an extension 3 times the size of your original house you could create too much resistance on one side of the ring (due to the amount of new cabling and plugs) and create this problem...
The current in the ring is directly proportional to the position on the ring. 10% of the way round means 10% of the current in the long side and 90% in the short side.
The other issue is that the ring circuit has a breakage and then only one 2.5mm wire is supplying the 31.9amp to the 4mm wire. This could overload the single, intact 2.5mm that's still connected to the consumer unit without tripping the aforementioned 32amp MCB. Of course this point is mute as the damn circuits gonna overload (if one of the original ring sockets then starts pulling 31.9amps) regardless of whether or not its got a 4mm spur due to the inherent flaw of ring circuits.
Yes. That is the fundamental flaw in ring circuits which everyone accepts.
The ring circuit (with its special dispensations) is really quite pointless since the introduction of the MCB which may utilise smaller cables than the old 30A rewireable fuses.
If the 2.5mm² were slightly bigger (32A instead of 27A) or there was a 27A MCB (there are 25A ones) then there would be no need for the special rules for ring circuits - I would say '
or their spurs' but actually there are no specific regulations regarding spurs so you may design anything that is safe within all the other regulations.
So swap the 32A MCB for a 25A one and all this debate goes out of the window (subject, of course, to the installation method of the cable but that applies to every circuit).
