PV Ultra swa

DC cable and in particular the recent innovation from Doncaster Cables 🇬🇧 and Sam Featherstone in PV ultra has had a lot of attention of late. While industry wrestles with the technical aspects around protective measures in play with DC systems we are perhaps missing the true intent of the problem to be solved. 

It seems the focus is drawn towards the buried aspect of DC SWA and allowing direct burial of said new innovation PV ultra SWA. However most installers would not ever bury DC distribution directly in the ground. Usually they would be in N750 ducts as arrays tend to be on the large side and often have more than one cable/conductor. Historically this was done with standard PV cabling with no armor or with a standard AC typical PVC/XLPE SWA constructed cable. 

PV DC cables, SWA or otherwise should NOT be buried directly in the ground. Pretty simple statement few would argue against and something I have said for a longggg time. Along with others. 

The armored aspect was largely in the fight to keep vermin and wildlife at bay. A mechanical protection if you like. It has crudely been suggested the use of an armored cable would in itself be a design admission of likely damage through to the inner conductors and raise question as to the selection of this particular cable type. However that is a rather basic assessment towards electrical design. We have many environmental factors that lead diligent installers towards selection and erection methods. Much like we don't always earth tray or other metallic containment methods carrying insulated and sheathed cables.

The issues installers face with PV DC systems is the locality to wildlife and vermin in outdoor areas. While innovation around arrays has led us towards safe zones protected from said intruders. The run up to these areas remains a challenge. Be that on ground mount frames, steel containment on warehouse roofs, through lofts, up walls, in voids etc. Even exits from said N750 ducts up towards ground mount arrays. 

This isnt just a challenge in the UK, I took part in a podcast with some international friends around this topic and was surprised to hear about innovations they use. Such as braided socks to place over string cables. I am not totally sold on those ideas tbh but I suppose as we attach PV string cables to metal framework the risk profile remains the same. 

We see the argument around reg 412.2 - wiring systems installed in accordance with Chapter 52 are considered to meet the requirements of Regulation 412.2 if: (i) the rated voltage of the cable(s) is not less than the nominal voltage of the system and at least 300/500 V, and (ii) adequate mechanical protection of the BASIC insulation is provided by one or more of the following: (a) The non-metallic sheath of the cable (b) Non-metallic trunking or ducting complying with the BS EN 50085 series of standards, or non-metallic conduit complying with the BS EN 61386 series of standards

It has been suggested this would mean PV ultra SWA would have to be within non metallic trunking or conduit but from my reading of that regulation I would strongly disagree. We have conductors that have basic insulation and are sheathed along within a bedding material before any metallic armors. 

I would view the cable as a manufactured solution that is enhanced beyond a simple sock covering to resist chewing rodents and wildlife. The whole argument/debate around locality to metalwork seems devoid of real world application of solar cable installation. Much of it is secured off roof surfaces and floors on steel/metal containment/solar rail. By nature it is always around conductive components. This then circles back to the question of keeping DC PV distribution separate from earth paths/parts on the AC side. Again this view enhances the selection of a cable type such as PV ultra SWA rather than direct people away from it. It is much more resilient against coming into contact with earthed parts akin to regular DC cables sited directly upon earthed frames and containment systems. 

Taking a cable into those areas with a high degree of resistance to vermin and wildlife is a great tool to have in the box. All innovated right here in Yorkshire, United Kingdom! Now when those events happen we end up with some exposed metal which can be identified safely during maintenance/inspection. Rather than having circumstances like those shared in the above images flapping in the breeze. That is the reality of the problem those in industry are keen to avoid. 

We do have a wider debate around earthing those armors and this blends towards a much bigger industry discussion around coupled AC voltages into framework on DC systems. Earthing roof mounted array frames and other such challenges. If we like it or not these currents and voltages are cohabiting spaces, containment and plant rooms together more and more often. We can either ignore it or do something about it. Much like Sam and Doncaster cables have done here. 

My view is this could be one of the most important global cable innovations for a very long time. One we should be proud was made right here in the UK with an industry supporting its adoption delivering safer electrical systems around the world. Imagine that! It is already multi award winning Electrical Contracting News 

For context and full disclosure I use PV ultra and PV ultra SWA at full market rates with no discount or paid promotion. For those who want to ask you can speak to Ben Griffin who supplies me with it often. I have no relationship with Doncaster Cables but do cohost the renewables podcast with Sam and am proud to do so. We covered this topic on the podcast a few months ago and I shared a video on my YouTube channel asking for others views on this in the hope of seeing what people think without me leading them. 

This is me setting out clearly what I think and why. Hope that is helpful and we will be going in way deeper on this topic soon in the hope its helpful to others via A121 electrical training and the renewables podcast. 

The above is before we even visit the aspect optimisation and other rapid shutdown protocols bring to the party in combination with an unearthed cable type such as this. 

Written by Mark Allison - Director A121 training Ltd