Some more questions

[moonpig]

Quote:

Originally Posted by moonpig

So on a 4mm 30/32a radial, you could branch off in 2.5mm without there being any problem with the 2.5mm cable branch not being able to carry the same load as the 4mm cable?

Thought 2.5mm T&E was rated 24A and 4.0mm 32A, therefore the 2.5mm couldn't carry the load

You are quite right mate.

Sorry i meant a fused spur/branch, but once again i was not very clearX(.

 

[Mr Sworld]

Thought 2.5mm T&E was rated 24A and 4.0mm 32A, therefore the 2.5mm couldn't carry the load

The branch in 2.5mm to one single or double socket is only carrying 13A maximum before it hits the 4mm 'backbone' 32A radial. (Remember a double 13A socket is only rated at 13A NOT 26A)

Even with a 2.5mm 20A 'backbone' diversity should ensure that the branch isn't overloaded.

 

[SPECIAL LOCATION]

Not now. I've just signed to E-On's green fixed tariff and they give you a free energy monitor.I now run around everywhere trying to figure out where the extra wattage is coming from!

For example, I am using 262 Watts at the moment which if I used that for 24 hours a day for an entire month would cost me

 

[moonpig]

Hey specs before you turn off your computer to save some wonga, could you tell me if i am right that you can spur off a 4mm radial with 2.5mm to one socket, and you can spur off a 4mm with 2.5mm to as many sockets as you like?

 

[SPECIAL LOCATION]

Hey specs before you turn off your computer to save some wonga, could you tell me if i am right that you can spur off a 4mm radial with 2.5mm to one socket, and you can spur off a 4mm with 2.5mm to as many sockets as you like?

Provided you have appropriate fuse installed in the branch you can spur as much as you like... ALSO providing that things such as max ZS, an max volt drop are not exceeded!

Try looking at it this way:-

Every single cable size has a maximum current rating it is designed to be able to carry safely. (manufactures spec's would give you precise figures.)

However tables are provided in the regs...in Appendix 4 "Current Carrying capacity & Volt drop"

from pages 274 onwards for various types of cable single core/multi core/PVC/Armoured... etc..

For each type of cable there are different installation methods referred to ..

e.g. surface clipped/conduit/buried in insulation etc.. etc..

from your cable size and installation method you will get a Max current..

As long as your fuse is lower than the max current you can branch where you like..

e.g table 4D2A pg 276 (multicore, Non armoured, sheathed copper cable)

for two core single phase, gives the following current ratings for various installation methods;

for 2.5mm 18A, 23A, 27A or 30A

for 4.0mm 25A, 30A, 36A or 40A

the third values in each case was the traditional installation method common in older properties..

Clipped direct or in masonry in NON thermally insulated walls..

In this case if your circuit had a 32A fuse, 4.0mm is fine for anything.. but 2.5mm (if not in a ring), needs further protection (13a FCU) cuz it cannot take 32a only 27 at best...

HOWEVER!

in the 17th those awfully nice IEE people have changed a whole load of installation method definition and have some special ones just for flat T&E in various insulated walls/ceilings, see pg 265!

this now also refers to a special current table 4D5..

which for 2.5mm now gives 21A, 17A, 21A, 13.5A, 27A or 20A

for 4.0mm 27A, 22A, 27A, 17.5A, 37A, or 26A

The clipped direct is still similar sort of value.. BUT the fixed in insulated walls etc.. drop the ratings right down in one case to 13.5A!!!!!

What I am trying to say and illustrate is that it can be a bit dangerous just giving a YES / NO answer on an open forum without clarifying some of the considerations that must be bade for general safety!

In principal what you are asking is possible providing correct fuses are installed along the circuit at appropriate branches.

You also have to take into consideration..

Load current

Overload protection device

Cable installation method

Suitable capacity of cable

Max volt drop

MCB/fuse time current characteristic.

Check thermal constraints,

As long as your cable size can satisfy all of the above

you can branch & spur where you like!

 

[moonpig]

Thanks again specs for taking the time to answer my quesions, and thanks for the pretty comprehensive answer.

I will have to have a think about some more questions for you, i reckon it will only take a couple of more post on the basic/easy stuff before we can get to the fun/harder stuff.