Hey guys. I have a technical question so decided to consult the experts - the legends on this thread.
What is the current trunking requirement for DC cables? Does it need to be metal? Was the "5“ requirement ever clarified?
And then, where does the trucking need to start? I have panels on a flat roof, with the cabling needing to run through the wall, across the ceiling, through another wall and then down to the protection box. Can the trunking start inside the ceiling (much easier installation) or do I need to find a way to have the metallic trunking pass through the walls?
It shall be as per the SANS10142-1 as the SANS10142-1-2 is still not released. My recommendation is to also investigate SANS60364-7-712
These will give you a very good answer.(I am just a bit lazy today to go and quote the various parts).
So trunking of DC cables, while metal trunking is not a requirement, it is a good practice. Where you might have a low insulation level situation your inverter would pick it up in the run to the array as well as the array. If your DC run is short, then normal PVC (UV stabilised) can be considered.
Trunking is NB where the cable is exposed to the sun, I do not believe any of the standards specifically cover that (but I might be corrected). The DC cable is supposed to be UV resistant and double insulated.
When the cables go into the house then anywhere where the cables are accessible it should be in trunking or where they can get mechanical damage. I had a difference of opinion with Jaco some time back and he convinced me it is okay to direct install the DC cables in the roof, where they are “out of the way”.
I am intrigued to why it has to go through the wall and not over? If you want to run it through the wall, I would still recommend conduit. If you run naked cable through a hole in concrete you do risk damaging the sheath/insulation. On DC cables this remains a NO NO! You want to avoid that at all costs!
Wrt going through the wall, the panels are on a flat roof adjacent to a pitched, tile roof with a ceiling. The wall under the pitched roof is built up right to the roof structure so the only way to get into the ceiling is through the wall.
Would a pvc conduit per string be acceptable for going through the wall, and then immediately after the wall merge the two strings into a single metallic sprague?
Something I’ve done in the past, is drill a 20mm hole through the wall. Mount the trunking directly to either side of the wall, so that it sits OVER the 20mm hole, with a hole into the trunking. Line the hole with a short bit of 20mm conduit. Voila. Neat as can be, easy to get the cable through, and no risk of damaging the cable where it rubs on the edges of the hole in the concrete.
On a practical level, the insulation on PV cable is quite thick and carefully threading it through a hole in the concrete should not damage it. After that… it is not going to move again, so who cares if the hole in the wall is bare. It just depends how OCD you are
So trunking of DC cables, while metal trunking is not a requirement, it is a good practice.
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I’m a convert to this method: I recently rewired my ‘new’ house electrical wiring. The original was done with steel conduit and these joined together at a number of 4x4 wall boxes. A bit strange but the subsequent sparkys dispensed with the conduit and ran their surfix cables over the ceiling.
Now P8000 trunking runs down the centre of each wing of the house and coinduit tees off to each fitting at the nearest point of the trunking.
Pity this system isn’t more common. I suppose the surfix curse is to blame :
Trunking threw the wall will also make things much more future proof in terms of adding or changing cables at a later stage down the line.
R400 or so to rent a hammer drill with the correct bit from your local Coastal Hire or similar, then getting threw a double brick wall is literally a 5 minute job.
SANS 10142-1-2 of which the 2021 edition was quickly withdrawn (if anyone can point to a final draft that can be read in the interim, please do - the two drafts found online are very old and differ)
SANS 10142-1:2021 should in all seriousness not be updated on a regular basis, if they do it is minor in nature. (Unless they go from Ed. 3 to Ed. 4, apparently Ed. 2 was a total waste of money).
SANS10142-1-2, still unhappy about the retraction. This has been theorised for YEARs and it seems that we will wait again.
So summary: Anyone’s guess is as good as the other as there are a lot of egos playing in here to delay it.
I cannot formally share the document as it remains copyrighted, but you can send me a quick message via e-mail (karel.rautenbach@offrian.com) and we can “chat” through it.
Thanks, much appreciated.
Wouldn’t it make sense to merge 10142-1:2021 and the 10142-1-2 re-release into one document, and publish this? It may be the scale of update that SANS 10142 users need to motivate many people to update and do a refresher.
Good Day All, I’m new here and came across this thread which has been very helpful. The case for metal trunking has bugged me for quite a while now and the way I see it, it is a matter of trade offs without one or the other being unanimously superior. This quote from Rautenk specifically stood out to me.
If your separate MPPT or inverter with built in MPPT has ground fault detection AND protection (clears the fault) metal conduit would make sense in the context of what Rauten said. Problem is not all MPPT’s have it. Of the Victron’s for instance only the Smartsolar MPPT RS has insulation resistance monitoring (i.e. just detection not even clearning) while the smaller Victron MPPT’s have nothing of the sort. The Sunsynks have it from what I’ve heard but I cannot vouch for that.
So my opinion (and merely an opinion) is if GF’s aren’t detected and cleared automatically I would feel much safer with PVC conduit (UV stable) all the way through ceiling to wherever the MPPT and Inverter is with each pos and neg in its own conduit while keeping them as close as possible to each other to still try and minimize induction loops (if not in high lightning frequency area). This way barring damage to the conduits the only place where insulation faults can occur is on the roof at the PV panels, not inside the building. Ontop of this I would double check my MPPT has atleast GF detection and ensure good bonding of PV frames.
Also take into account if your PV system is ungrounded i.e. no SYSTEM GROUNING (both pos and neg are floating) you would need to encounter 2 ground faults before fault currents can flow.
So I believe running in PVC this way is the safest(perhaps overkill) in terms of avoiding insulation faults and potential arcs and fires.
But it comes at the cost of not having absolute minimum induction loops and slightly increased risk of induction surges in high lightning areas. Plus the other pro’s of metal trunking such as strength, heat dissipation if heat source is cable inside etc. are lost.
Perhaps if others here can add more benefits of metal trunking it would help as I probably don’t see them all. For instance perhaps someone can elaborate on EMI (electro magnetic interference) benefits since I am a layman on this topic.
