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Installing AWA in Trefoil

gibb01

Hi All,

We have a project installing a 630A Panel board from an LV panel board within the same room.  Due to space constraints we no longer think the 300mm SWA we were looking to install is going to be physically feasible.  So we've been looking at running 300mm AWA's in Trefoil instead. It's a short run of around 13m & the panel board is going to contain a mixture of different loads.

We're obviously using the Aluminum glands & terminating into an Aluminum plate either end, however not having had to install cables in trefoil before - I'm not sure if there is anything else we need to be mindful about. 

It's being installed on a 450mm ladder & I've checked within table 4C5 for spacing factors. I'm unsure if the neutral should be installed as close as possible to the trefoil? It's also been mentioned that Quad cleats are available to include the Neutral, Lastly it's been mentioned about potential single point bonding of the conductors - again something I've never had to do before.

I will be looking to get a design carried out, I just wondered if anyone had advice as it's not something we've had the need to carry out beforehand - So unsure whether there any pros / cons of doing this way as opposed to a standard 4 core SWA (Other than the physical impracticalities!)

Many thanks in advance. 

Tim

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  • 0

    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

  • 0 in reply to gibb01

    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.

  • 0 in reply to mapj1

    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. 

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  • 0 in reply to mapj1

    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. 

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