Installing AWA in Trefoil

4 core SWA of that size is almost unmanageable in a confined space, it is more applicable to burial. Or to long runs cleated along a structure.

Single core AWA is commonly used for this sort of application and is bit better to handle. If reliance is being placed upon the aluminium armouring for earthing, then it needs connecting at both ends. Single point bonding  can give slightly higher current carrying capacity on long runs, but is insignificant on a short length as is being proposed.

When terminating large single core cables, beware eddy currents in ferrous metals ! Aluminium is fine, but double check that this is actually used and NOT STEEL.

A large bonding conductor is probably required between the aluminium gland plate and the main switch-gear enclosure. Reliance on the fixing bolts is unwise at this sort of current.

I would use cleats that support all four cables,.

Broadgage's comments are helpful.

Do be mindful of the fault rating of any cleats you select; reputable manufacturers will state it. If you do use a cleat per core (rather than a quad or trefoil cleat) make sure they're not steel ones designed for multicore cables. Personally I would also be mindful of routing around other steelwork, for example support struts across the cable entry and incidental loops like bolts securing cleats (others may consider this OTT)

I presume for this size you're not looking at parallel conductors but if you are the phase rotation and placement of conductors within the bundle can affect the current sharing. Normally the neutral is bundled with the line conductors or fixed adjacent to the trefoil.

For the length - and I don't know what your load or protection is - I doubt you're considering reduced neutral but it is an easier conversation with singles. More likely with parallel circuits, e.g. 3 per phase and 2 neutral. You may require overload protection for the neutral though.

I did a similar install a few years ago, we needed to supply a new panel board from the existing DNO head/isolator, around 8 metres to the other side of the small room. We settled on tri-rated 185mm parallel cables in 200mm trunking, as there was no way we'd be able to bend the 300mm swa around the corners of the room.

Many thanks for all the replies. That was our other thought to install Tri rated singles in parallel. It's a toss up between what's going to be easiest and cost effective!  

Thankfully it is a reasonably straight run with a single horizontal 90 on the ladder then down to the new panel. We're not looking at parallel conductors, as the 300mm should suffice for the 600A we're looking at. We also are installing a separate 120mm CPC.  Its the coordination of the phases within the trefoil and the position of the neutral (if this can have effect on current rating) that I still don't don't quite have a grasp on. Again, many thanks for your input.

Tim

There are two things to consider when tri- or quara- filing wires. the first is heat, and that wants you to spread them out into many separate strands, fresh air between and get a good current rating, and the second is magnetic fields, which manifest as an additional inductive voltage drop, and coupling of induced currents into adjacent structures. That unfortunately says you want them as close as possible - currents only perfectly cancel when the flow and return currents are based on the same geometric centre (so for high frequencies, like radio,  where this inductance is a show-stopper, we use coaxial cables.)

The result is something of a compromise. Neutral usually carries less current so can be further from the bundle for the same magnetic effect, but there is not a lot in it, especially with unbalanced phases and or electronic loads.

When it gets bad we make many strands of each phase and bundle them so that in each triplet or quad  currents are more or less summing to net zero, but each bundle only makes a fraction of the heat and the bundles  can be spaced out.

Mike.

I think most DNOs will not terminate tri-rated cables at the supply end, at least UKPN will not. Also they will not earth AWAs at their end so you will have to earth them at the load end. This is to prevent circulating currents in the armour. You will need to run a separate earthing conductor in parallel to provide the means of earthing for your installation. 

An important factor in the design when single cores are installed on racking, is the bursting strength for SC conditions and the spacing of cleats. 

Jaymack