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.

 

[Wilson12]

So if they arnt supposed to go in conduit. What can I use for a radial socket circuit in a workshop where vehicles may be?

 

[happysteve]

So if they arnt supposed to go in conduit. What can I use for a radial socket circuit in a workshop where vehicles may be?

Singles!

 

[davesparks]

So if they arnt supposed to go in conduit. What can I use for a radial socket circuit in a workshop where vehicles may be?

Steel conduit or micc are the toughest wiring systems commonly available. SWA is toigh, but not impenetrable as some people seem to think.
Steel conduit would be best suited in my opinion

 

[Wilson12]

So would e.g 5 single conduit runs look stupid or is that common.
If they are run to a simular area
Cheers

 

[Wilson12]

That dosnt sound practical to me but to get around this situation are singleslots of normal

 

[Wilson12]

Can anyone help with this?
Much appreciated

 

[Leesparkykent]

Singles in conduit is the standard way not T&E in conduit.

 

[Wilson12]

Ohh so not single conduit with twin and earth
If there are five circuits in a close area which will.a simular route from.the distribution board and they need to.be mechanically protected.
What can I do if enclosed systems won't allow e.g 2.5mm2 for sockets

 

[davesparks]

What can I do if enclosed systems won't allow e.g 2.5mm2 for sockets

Use bigger cable or seperate pipes.
Has your tutor not taught you the course before giving you this work to do?

 

[Wilson12]

Nope. We have to research which is tricky,with a question like this. I get you can use bigger cable but it's more practical to use 2.5 in sockets so would I be stupid to have e.g five conduit runs all going uo to the same perforated cable tray

 

[davesparks]

I think you need to ask the tutor to actually do some teaching here as they are obviously asking you to do something well above your experience level and current knowledge.
You wouldnt normally expect conduit to be paired up with tray except when the conduit is beong used as a decorative rather than functional containment.

What course are you doing and how far tbrough it are you? Is this part of an apprenticeship?

 

[Wilson12]

Its a level 2 electricial and installation.
It needs to be mechanically protected. But you say conduit isn't usually used for twin and earth.
Also I can't use a tray system at the ceiling being convenient with the conduit then dropping down to sockets.
And trunking and conduit won't allow you to use 2.5 due to grouping and it can't dissipate heat.
Well I'm soo lost to what the solution is then. I'm sure it's just a straight forward thing but it's taken me all day to research and I'm still no closer

 

[davesparks]

Youve already had the answer, which is to use bigger cable. Its not our fault if you want to ignore the answer when its given to you.

The normal way of installing such a system is to have one main run of trunking with a conduit taken from that to each point.

 

[telectrix]

as dave says. then there is no grouping factor in the conduit as there's only 1 circuit in it.

 

[Wilson12]

But then it's the same? Just grouping in the trunking
Thanks for the help though

 

[davesparks]

But then it's the same? Just grouping in the trunking
Thanks for the help though

Yes you apply grouping as necessary for the trunking, then select an appropriate cable size

 

[Wilson12]

The trunking is enclosed so it's the same grouping (Cg) amount in table f3 as conduit?