Conduit

[Wilson12]

When calculating cable sizes...
When I want runs to be enclosed in conduit or trunking.
The grouping (Cg) makes (it) the cable size very large..
What am I doing wrong when calculating enclosed cable size.

An example would be a radial circuit ran with 4 other thermoplastic cables
In =20/ ca=1/Cg=0.65 /cf=1
It = 33.3 a
Using f6 tabulated ccc
Means I have to use a 10 mm2 cable

Looking at this if I wanted to use 2.5mm2 I can't use more than 1 cable in conduit???

 

[telectrix]

33.3A is well in for 6mm. just borderline for 4mm. also, you need to use Ib for calcs. not In.

 

[Wilson12]

Yes ib and in would be the same in this case.
Which reference method did u use in table f6
And it's not possible to do more than one cable in 2.5?

 

[Leesparkykent]

All the enclosed circuits will be running at 20A for 100% of the time?

 

[Wilson12]

Two 20amp isolators and two radial socket circuits.

 

[Leesparkykent]

Two 20amp isolators and two radial socket circuits.

What equipment are the isolators supplying? Whats the intended use of the sockets? Cleaners sockets, general use,etc

 

[Wilson12]

I'm doing coursework and it dosnt specify but it's in a workshop

 

[Wilson12]

Which reference method should I be using in f6

 

[Richard Burns]

You normally use single core cables in conduit which would be table F4.
Use reference method B.
Without knowing the actual load you are a bit limited so have to use In as the design current.

 

[Wilson12]

Cheers and what would u suggest to use instead. As the cables need to be mechanically protected being in a workshop area.

 

[Richard Burns]

If you have two runs of conduit spaced apart then you can use 4mm² single core cables with two circuits in each conduit.

 

[Wilson12]

So I can't use 2.5 for the sockets

 

[davesparks]

What course are you doing this for?

 

[Wilson12]

Design lesson
Also which reference method is conduit on a wall for f6 page 155

 

[Richard Burns]

They do not give a reference method for twin and earth cable in conduit as it is not meant to go in conduit.
If you use the values in F5 you should be OK, just don't push the limits.