Cable Fill ratios

[peterduckett]

Im trying to work out cable fill ratios for trucking or conduit of twin and earth and looking for a bit of help;

Im trying to run 5 cables into the loft and would like to hide them in a wall/ trucking not a fan of clipped and i know conduit is only really of singles but it seems an easy way for future proofing

1 x 10mm cable
2 x 2.5mm cable
2 x 1.5mm cable

What sizes should i be looking at ?

 

[Chri5]

I was always taught to never have more than 70% of the containment space occupied when finished with cable runs.

Is the 10mm for shower and how close is it to the design limits ?

Reason being that adding it in to containment with the 4 x cables will derate for grouping.

I did suggest in your last post that you get some small cuts of conduit and 'play' with them for sizing / cable volumes- did you try that ?

If doing plastic conduit I'd go 3 drops x 25mm

If doing plastic trunking I go 2 x drops- 2.5mm + 1.5mm's in 40 x 16mm and the 10mm in 25 x 16mm.

 

[peterduckett]

Yeah the 10 mm is a shower at 45 amps
IT will be connected to the beams in the loft so not laying over the insulation and in the conduit for one wall say 2.5m

Assuming conduit is the worst de-rating the cable will still be able to provide the full 45 amps needed,

though if you used trucking would de rating be much of an issue if a sutible size was uses

 

[GaryMo]

Reason being that adding it in to containment with the 4 x cables will derate for grouping.

Cables loaded at less than 30% of their rated capacity can be ignored.
Also, the factors listed in 4C1 are for cables that are equally loaded.

 

[ban-all-sheds]

Cables loaded at less than 30% of their rated capacity can be ignored.

What about cables which are loaded at 100% of their capacity but for less than 30% of the time?

 

[holmslaw]

..

 

[GaryMo]

30% of what time? I take it you're talking about the 10mm2 cable supplying the shower?

I was getting at the liklehood that an upstairs ring final and upstairs lighting circuit, for example, may possibly be omitted from grouping calculations.

 

[GaryMo]

30% of what time?

I was getting at the liklehood that an upstairs ring final and upstairs lighting circuit, for example, may possibly be omitted from grouping calculations.

Uniform groups of cables, equally loaded so same size conductors, same loading (Note 1 under 4C1, p268).

 

[peterduckett]

Oh dear this is not going to be easy!

So has anyone got an ideal arrangement of conduit / trucking to fit to put these cables in

 

[GaryMo]

So has anyone got an ideal arrangement of conduit / trucking to fit to put these cables in

Chri5 answered that above.

 

[ban-all-sheds]

If doing plastic trunking I go 2 x drops- 2.5mm + 1.5mm's in 40 x 16mm and the 10mm in 25 x 16mm.

Might as well use 40mm wide for all of it - easier to get some clips in to support the 10mm².

 

[peterduckett]

Cables loaded at less than 30% of their rated capacity can be ignored.

Are you saying that any lighting circuit wired on 1.5mm 18amp cable protected by 5/6amp would never reach 30% or their about of its loaded capacity

 

[ban-all-sheds]

1.5mm 18amp cable

What reference method gets you to 18A for 1.5mm²?

 

[peterduckett]

http://www.tlc-direct.co.uk/Products/CA1dot5G.html

 

[ban-all-sheds]

1) That is not a reference method, it's a wholesaler's web page.

2) Are we to take it that you are attempting to do electrical design work without having access to details of installation methods, de-rating factors, tables of current carrying capacity and voltage drop, etc?