Doubling up conductors

[Amp David]

Is it an exceptable method to double up conductors in a 4 core cable to increase the CSA and then put in a seperate CPC?

If so, then as there are no tables for doubled up sizes eg. 5mm, 8mm squared etc, would it just be a case of doing the calcs for the single core size then dividing by 2

 

[High Tower]

someone told me that as long as they are exactly the same length then you can but please dont take that as gospel, i dont know how reliable it is

 

[tonys]

Do you parallel them up?

 

[johnboy6083]

Yes. In some situations its the only way, because it means smaller cables canbe used, with smaller bending radius ect. As for calcs, current carrying capacity is doubled, voltdrop and resistance is halved. Don't think though that you can use the values given for a 50mm2 cable for 2x 25mm2 for example, as the 50mm values may take other things into account, ie capacitance.

 

[topquark]

I would say that it's fine for cpc but for phase conductors no. If you dropped one of the connections for a cable in parallel then you'd run a very high risk of overheating.

Even if it's a distribution circuit only terminated at either end, I still wouldn't risk it, with what device would you protect the cable?

 

[johnboy6083]

In my experience, it's only ever used with distribution circuits, or radial circuits, that are wired with SWA. Both cores of each phase and neutral must be terminated at the same place, and the cables must be the same length, so the load is split evenly across the cores.

 

[topquark]

I guess if you took each core into a separate MCB/RCBO then that would be safe but definatley not both cores into one protective device.

 

[johnboy6083]

I've installed parallel cables onto the same Acb before. Most large incomers are parallel cables installed onto the same fuses or mccb/Acb. I was looking at one today. It would something pretty violent that would cause the loss of one phase conductor, and IMO, the kind of condition that causes that would probably be more likely cause a short, causing near instataneous operation of the protective device.

 

[Mr Mike]

Hi Amp David,
As johnboy has, so have I have installed SWA in parrallel, again into an Acb.
At the time the MEB (Midland Electricity Board) were required to certify the installtions at the job; it was for public use and they had no problem with the parrallel cables.
Hope this helps some
Kindest regards
Mike.

 

[Engineer54]

Hahaha, Running parallel cables is standard practice, it can increase current carrying abilities enormously. Example a 300mm csa cable is required for say a given load or sub-main. If you run in 2 x 120mm cables the cost of cable is reduced, the current carrying ability is increased, volt drop halved etc etc.... I've been on projects where each phase from a transformer was run with 9 single core cables on tray to the Main Distribution Board.

paralleling distribution cables works, and it works VERY well!!!!