4mm radial

[sedgy34]

has anyone spured off a 4mm radial in 2.5mm on 75 mtrs circuit length on 32A mcb

 

[Strima]

It wasn't me, didn't see me, can't prove a thing... :lol:

 

[sedgy34]

It wasn't me, didn't see me, can't prove a thing... :lol:

CHILL apparently its acceptable

 

[Engineer54]

I can't say that i've ever had a 4mm socket based radial circuit run out to 75m, let alone spurred off of one...lol!!! Is the spur to make it a round 100m run?? lol!!!

 

[Baker1988]

How is it acceptable 2.5 can only take about 25/27 amps so how can you pretect that with a 32 amp breaker

 

[Baker1988]

And doesnt the regs state that if you doen grade a cable size it has to have a a adaque over current device like a fused spare or some thing

 

[Baker1988]

Down grade

 

[telectrix]

question is. with a radial circuit, you don't spur off, you extend the radial or branch off. why consider using 2.5mm? why not 4mm?

 

[Top Cat]

^^^agree^^^ i don't see a problem with 3 x 4mm in a socket.

 

[SPARTYKUS]

Baker1988

yes you're right about the 2.5mm2 only being rated at less than the 32A MCB.

But the 32A MCB is protecting the whole circuit, not JUST the piece of cable (the 'spur') to a double gang socket. The double gang socket is limited to two plug tops, each could contain a 13A fuse. 13+13 = 26. Are you seeing a way out here ....

So if you spurred off the spur, again in 2.5mm2, well then you're asking for (theoretical) trouble, as now you have 2 x 26A potentially going through the 1st, original bit of 2.5mm2 cable. Which would trip the 32A MCB sooner or later, but a bit less and maybe it wouldn't, and then you'd have a cable with a lower current carrying capacity than the current its carrying! Not good. Thats why that's not allowed.

The reason 4mm2 is ok to do this with is it will take 32A and a bit more quite happily, and the 32A MCB will trip before the cable is troubled by excessive load. Assuming the installation methods, ambient temperature, and so on are all acceptable of course.

 

[SPARTYKUS]

P.S.

related to thread (sorry OP for hijack)


I saw a ring (2.5mm2) the other day with a DG socket spurred in 4mm2. From that was another DG socket in 2.5mm2 spurred. That was the end of the line. All on a 32A MCB of course.

Now, I can't actually think of a hard and fast reason to condemn this - what are others' thoughts. Is it simply that it is not a standard circuit in the big Green book? As far as safety is concerned I can't also see an issue with CCC for the two spurred sections either.....it just doesn't sit well.

 

[Plonker 3]

But you can spur off a socket on a ring final circuit in 2.5mm to one point and that is acceptable. Although doing what the OP has stated isn't

 

[SPARTYKUS]

But you can spur off a socket on a ring final circuit in 2.5mm to one point and that is acceptable. Although doing what the OP has stated isn't

Hi Dillb - in what way not acceptable? I'm looking at a picture in the regs of a 2.5mm2 spur from a 32A protected 4mm2 radial....

 

[Engineer54]

^^^agree^^^ i don't see a problem with 3 x 4mm in a socket.

3 X 4mm = 12mm ...most UK accessory cable terminations are now only suitable upto 10mm. Even then, the terminal screw is at it's most extended position, and often clear of any screw shields... Getting a 2.5mm into a terminal that already has 2 X 4mm is a bit of a struggle!! These cable terminals were at one time, suitable upto 12mm but was a while back....

 

[sedgy34]

sorry guys meant branch of a 4mm radial circuit with a 2.5mm to a double socket