Can you use SWA for solar PV DC distribution buried in the ground.....

[@protectiongeek]

Another great video, Mark, that gets the grey matter working. I have to say, however, as a retired DNO Protection and Control Engineer there is perhaps a danger of overstating the hazards and risks associated with DC distribution and an equal danger of reinventing the wheel - not by you, of course, but the industry in general. A typical DNO Grid Supply Point (say 275/33kV) uses DC very widely over thousands of metres of SWA cable, earthed via glands at both ends of each cable. Now, I accept that these cables don't necessarily carry the same level of voltage (a typical tripping battery at a GSP floats at about 125V), nor do they carry significant currents for hours on end but neither of these parameters should really obviate the use of SWA, how the armour is earthed or how earth faults on these cables are monitored and protected against. I do, on occasion, wonder at the rationale behind some of the regs included in BS7671. As an aside, I have recently installed a short section of an EV Ultra style cable (although not the actual EV Ultra product) to provide power and data in one cable to a small outbuilding. It is a 6sqmm 3-core + CAT 6 data SWA cable and is ideal for the application. The very short (about 1.5m) section that is buried is within a 40mm service rigiduct for additional mechanical protection.

[@colingoode3702]

Interesting subject & one that I have experienced first hand - as a homeowner. The first part of my solar / battery system was installed in March 2023. 10 x panels, 3.6kW GE Gen2 Hybrid Inverter & a 9.5kWh GE Gen 2 battery. The installers used SWA for the 2 x DC strings from the roof down the back of my house & then buried a section of it under some existing gravel next to a paved walkway up the side of my house before it enter my attached garage where all the gear was mounted next to my replacement consumer unit. A nice tidy solution. 1 year later I decided to add 5 extra panels & an extra 9.5kW battery. This would involve re-stringing the original 10 panels (ESE facing) into a single string (no shading issues) & adding the 5 new panels (NW facing) on the 2nd string (max 2 strings on my GE 3.5kW inverter). All good I thought except my installer said that they would need to replace the original SWA cable with a new PV Ultra cable to meet new regs that prevented SWA being used for DC because it wasn't double insulated. OK I thought but, there was a snag. The installer said that they couldn't bury the new PV Ultra cable under the gravel up the side of my house. Instead it had to be clipped externally to the side of my house 2m above the ground. So I have gone from a relatively tidy buried cable to a highly visible chunky cable running down the side of my house. Question. Would an armoured version of PV Ultra allow it to be buried under the existing gravel next to the house brick wall as per the original SWA, without the need for any additional trunking? I'm just looking to make the install look a bit tidier & less obvious.

[@electrician247]

Direct burial is tricky with PV ultra in SWA form imho. Can be engineered to a safe state via optimisers and inverters monitoring for fault conditions. But it would be a deviation presently to regulations in my view. A simple work around would be to use a 750N duct that way you can use PV ultra with or without armours. One a good installer will help you with.

[@CaptainProton1]

If I had a sip of beer every time you said 'In and of itself' I would be quite drunk by now :)

[@markrainford1219]

On a schoolday?

[@electrician247]

Enjoy the drinks

[@seymourpro6097]

The trouble at the moment is that by the time a solar job gets from customer enquiry to job completed the regs will have changed at least once.

[@electrician247]

The guidance books definitely will lol

[@EverydayLife621]

.. if practically possible just sleeve all cable (incl. armoured) individually with PP Flex Conduit (~£1/m if only needing 25mm) as if the cable needs replaced, it gives a chance to be pulled through again rather than digging the trench out again.

[@justingrant3346]

Hi, Thanks for the video and weblink. Is Graham Kenyon (webinar) video on KZbin or do I need to sign in to the IET website to view it?

[@effervescence5664]

Cable selection is always a pain, arguably in times gone by we would of just used junction boxes to swap from SWA to PV Ultra or alike depending what you're trying to achieve. I can understand not wanting to introduce a fault path that's unregulated to the system but potentially an RCD could prevent the issue installed on the DC side. The trouble is no installation is cookie cut and technology is moving faster than the regulations can keep up or predict.

[@electrician247]

100% the regulators will be obsolete if they don't adapt. That is my worry atm. This will be taken out of their hands due to roll out demands etc.

[@YewDuct]

I'm looking to relocate inverter and batteries from the loft (where the installer dumped them on the beams in 2021!) to the garage, where the batteries can be in a climate controlled cabinet kept warm by a radiator on my ASHP return flow so that they don't get cold and shut down or charge slowly any more in winter when they are of course most needed! I'm intending to use Doncaster Cables' PV-Ultra non-armoured version as the cable will nearly all be indoors, aside from a 1 metre bridge (lintel) between my home and my garage. Doing my homework, provided you have galvanic isolation from the AC, I learned that either DC conductor can be earthed (so the PV voltage is relative to earth) and it would seem to me that if you do that, then you could also bond the armouring on the armoured version of PV-Ultra. However, for my 1 metre bridge I'm well aware that metallic conduit is not allowed because of the risk of high voltage DC arcing so something like your double wall tube would suffice. I've been spectacularly unsuccessful in identifying any ducting products intended specifically to meet PV DC standards! My interpretation is that earthing the armour on PV-Ultra without also earthing one of the conductors would fall foul of the same constraints - i.e. you would be introducing the potential for high voltage DC arcing between conductor and casing, and thus it should normally be kept isolated and its role be purely for physical protection of the cable.

[@gino2465]

That os a brilliant set up. Have you seen the price for these snart clever units . Add them up per pannel. It puts on 2k per system

[@TheTechOnline]

How would you terminate each end of the duct? I have a run I need to do between my garage (separate building) and to inside of the house. I could core drill on the garage side but would rather not on the house side. I was thinking bringing the ducting up into a small manhole (earth rod pit) and then running out there and clipping to the wall. What's your thoughts?

[@electrician247]

Lots of ways to do it. Manholes of some description usually the default approach. Just ensure the ducts are sealed well. They often flood or allow access to rodents. Special sealing compound is available.

[@alexrakhshani7588]

Interesting topic, this surly makes a DC SWA cable not fit for purpose. Armour is classed as mechanical protection, if that could become live under fault conditions and earthing it poses a "potential danger", surly its safer unarmored and installed in a duct. This also questions earthing arrays and bonding DC equipment to an installation. If you have a potential to introduce un isolatable DC voltage to the equipotential zone, it makes sense to me to have full separation between any DC components and AC installations? How long before optimisers are mandatory in all installs.

[@electrician247]

Viewing the armours as "earth" in terms of ADS i agree. But in the DC world using double and reinforced insulation it doesn't work in the same way with ADS. However those armours can aid lots of other routes to safe states via faults. With capacitive coupling and such a lot of mechanical damage to DC PV cables this is a much needed innovation and will be everywhere inside 12 months.

[@BROOMEngineeringTMIET]

This looks more like the regs being used to market new products for manufacturers.

[@electrician247]

Or perhaps a move to put safety before profit. Solar fires and accidents are no joke around the world. We seem to be last to adopt optimisers and such in terms of safety. Also it has to be said the regs are not currently suggesting ANY of this is required.

[@BROOMEngineeringTMIET]

@@electrician247 I would be interested to see any safety data to try and ascertain the associated risk of using conventional SWA for DC solar PV applications, and how many fires and accidents are attributable to using SWA. I thought using SWA between panels and inverters was now frowned upon? I suspect there are far more issues on the strings, (poor quality) MC4 connections, and cabling under / around the panels causing fires / safety issues than any SWA cables.

[@electrician247]

@BROOMEngineeringTMIET you seem to be drawn towards the SWA aspect alone which is strange. The issue is distribution of DC voltages on PV systems when buried. As shown in the video that doesn't need to involve SWA. However benefits can be found with the right setup. Data at a global level due to rodent and vermin damage is substantial. The issues around MC4s and DC isolators usually boil down to poor installation by operatives. Usually the same operatives selecting inappropriate cable such as standard SWA which does not allow for double insulation between polaritys and potentially earth. The insinuation towards manufacturers making money is negligent towards the safety impacts on solar arrays. We should do better and innovation such as this can allow for that. A strange approach to want to argue against that tbh.

[@BROOMEngineeringTMIET]

@electrician247 yes - I most definitely am struggling to get my head around why we now seem to have an issue with cables that have historically been ok with 400+V between conductors, albeit AC, and the regs have clearly stated that these cables are ok for DC applications. So then it raises the question of whether the regs are increasingly becoming a marketing tool, both for new products. Why would vermin activity be a greater issue now than previously?

[@electrician247]

@BROOMEngineeringTMIET you understand the protective measures for DC PV are double - reinforced insulation and not ADS as with AC distribution. The single insulated conductors and earth path are the reason that is allowed for AC or DC that isn't derived as PV which uses a protection method of class 2. This isn't a new concept. It's been regulated for decades. The vermin activity is defeating the protection method of those double insulated non SWA properties resulting in countless failures, repair work and worse. Having a steel containment with a bespoke PV cable akin to SWA helps mitigate that. It's not that complicated tbh. A strange view to believe manufacturers have that much influence on regulations. Input to JPEL64 yes. Control? Not even close lol

[@fredflintstone1428]

I do like your channel, but on this topic I find myself asking, what is the chance versus risk. For example, if someone is digging up the ground where an overhead PV system is located, shouldn't they identify where that power is going before setting to? I think in most circumstances, you can't regulate or legislate ignorance or downright stupidity away.

[@electrician247]

underground strikes are surprisingly common for utilities and consumer owned systems. Having the right duct/installation method is key to avoiding it. Installed correctly as I am trying to outline here, with cable marking and plans etc actual strikes can be elimated/reduced. The fault detection aspect is very much more around rodent damage (very common), landslip and such. Thanks

[@octymocty132]

Nyj c all the way ?