Hi all. This looks like a nice place...(replace flannel)

If I've got it right, the reason taking a spur from a spur is bad (unless protected by an FCU) is that the MCB in the CU is chosen assuming the presence of the two conductors in the ring, and that too much current could be drawn down the spur cables..yes?? If this is so, why can't you take any number of spurs from a socket in a radial circuit? I can't visualize why adding a spur in a radial circuit is different to just extending the circuit - sorry if this is stupid but it's like trying to visualize 11-dimensional Superstring Theory to me.

I'm not sure if that's even relevant, but what I've got is a radial circuit coming down from the loft to a wall socket from which a cable then crosses a doorway by going *under the carpet* (don't ask - wasn't my doing) to the next socket and then finally onto the fridge socket in the kitchen. I don't want to traverse the doorway by going under the floorboards because there's a gas pipe really close to were the cable would emerge under the boards. Can I use some kind of cable connector to split the cable in the loft to go down either side of the doorway? i.e. one 'arm' would supply one socket, the other, two sockets.

One other thing if I may: this radial circuit, plus two others which supply one socket in each of two bedrooms are all coming from one 16A MCB in the CU (I think it's all 2.5mm twin and earth cable). Is this bad - shouldn't it be a 20A MCB?

H

The technical explanation isn't really relevant because you could feasibly string 10's of sockets in an extended spur, each of which could draw miniscule amounts of current so it won't trip the protective device.

Adding a spur to a spur goes against the 16th edition wiring regs so it's a no-no.

You also need to think in terms of the protective conductor (the earth wire if you will). If you've got spurs on spurs then you will have the earth being made and broken at each spur using a terminal block connection. If you happen to break the earth at some point in the chain then none of the following spurs will have an earth - scarey!

HM

[quote author=Lectrician  link=1101274475/0#1 date=1101282329]A radial circuit can safely be wired as a star arrangement with branches everywhere   [/quote]

When you say 'star', does every leg of this star have to start from the mcb or could this star start from a jb somewhere along the radial circuit?  ???

I still don't understand why in a radial circuit the regulations put a limit on how many sockets can be connected to a branch (spur). I don't really understand the earth point either as wouldn't it be interupted anyway at each socket in the main radial circuit?

But if I understand Lectrician, it is ok for me to cut the cable in the loft, add a junction box, and have a branch going to one socket on one side of  the doorwar and another branch - or is that the main trunk (?) going to the other side of the doorway to the two sockets; see, here again, I can't see the difference between a branch (spur) and the main trunk of the radial circuit.

Sparkyjonny, thanks, I did understand that.

H

Quote:

Yes.

Quote:

You can.

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It's not

[quote author=HarryH  link=1101274475/0#6 date=1101325381]I still don't understand why in a radial circuit the regulations put a limit on how many sockets can be connected to a branch (spur). [/quote]
They don't.....

rings do have thier place but i really can't see what is wrong with properly installed radials TT

the ring cuircuit was designed to allow two 3KW heaters at arbitary locations and a few small appliances on top of that whilst minimising cable use (iirc it was introduced in a time of copper shortage).

in some ways i think the way to go is a 20A radial per room possiblly also running the lights via a FCU off that same radial (though that does raise RCD related issues). This way when you want to do work in the lounge that involves the electrics you just turn off the breaker marked lounge and leave the rest of the place totally unaffected

I may be wrong but if I recall the UK is about the only EU country that wires with rings - radials are the order of the day in most other EU countries.

RR

[quote author=plugwash  link=1101274475/0#10 date=1101347295]in some ways i think the way to go is a 20A radial per room possiblly also running the lights via a FCU off that same radial (though that does raise RCD related issues). [/quote]
And issues of if you want to do the work when it's dark, you lose the lights in the room as well....

And thanks for everyone's patience..

Rings will die soon.....along with bs1363      

what i don't see is why they don't make a 13A socket with a built in fuse for protection and shutters that are designed so a europlug will open them

harmonisation problem solved at least for small portable appliances

[quote author=Lectrician  link=1101274475/15#18 date=1101405143]Rings will die soon.....along with bs1363       [/quote]
No more rings?   Not such a bad idea.

No more fused plugs?   'kin terrible idea.


[quote author=plugwash  link=1101274475/15#20 date=1101416588]what i don't see is why they don't make a 13A socket with a built in fuse for protection and shutters that are designed so a europlug will open them [/quote]
How about because some appliances/appliance flexes need less than 13A?

Just because we're unusual it doesn't mean we are wrong.

the harmoisation of portable equipment makes a lot of sense both for manufactures and for customers.

the one part of portable appliances that hasn't been harmonised accross europe yet is the plug and socket system. For low current class 2 appliances the europlug is now usable over almost all of europe.

for higher current kit the combined schuko/french plug is also starting to replace local plugs in quite a bit of europe.

the UK plug system does have its advantages but I would say its days are almost certainly numbered.


fixed wiring is another issue but making the color code the same as that for portable kit was probablly a sensible move

I prefer radials these days as if a connection come loose or a cable is broken then you lose part of the circuit which highlights there is a problem where as with a ring the circuit will continue to work without showing up any effects.



saying that i still wire plenty of ring cct's

A 16 or 20 Amp radial can be wired in 2.5 all the same

It is rare that I wire a 4mm 32 Amp radial

one of the reasons that 4mm is so much more expensive than 2.5 is just the volumes produced,n i use thousands of metres of 2.5 but barely any 4 and with the increasing wattages of showers and Range cookers I am using more and more 10mm as opposed to 6