I accept the corrosion issues.
I was at Cabstrut recently and they quoted me on a new aluminium cabstrut that they now have.
Pity the marketing dept hasn’t got it on the website yet (an advantage of being a fat cat on the Bidvest gravy train)
It looks like DIN rail with similar elongated slots in the sides…(R360/6m ex Vat)
1 Like
That can work. Nice to know it exist. Cant help to wonder what caused them to develop this new product. I guess the renewable energy demand played a role.
The anodized coating on aluminium is not a good conductor and earth clips etc. need to pierce the anodizing. For DIY home install it’s simple to bond panel to panel and take care of galvanic action. My comments are confined to Unistrut type mounts (subject in case) I never knew SANS allowed bonding of just the mounting structure so thanks for that. I’m aware that other countries require panel to panel grounding regardless of the system used so there may be good reasons do so, maybe belt and braces.
1 Like
I worry about strength or deformation in high wind loads. I have used it before as well as the anti theft clips and now used rails and clamps (Renusol)… More peace of mind.
1 Like
If my chemistry is not completely deserting me, the outer layer of aluminium actually oxidises (aka rusts) and forms a layer of aluminium oxide, which then protects the rest of the material. You can improve this process by anodising the material, which is essentially electrical treatment that makes this layer even thicker. For solar panels, this also makes the material harder, so it does not dent or bend.
What I found somewhat interesting, is the decision of what fastener to use with those aluminium rails. I’ve always used stainless steel, which works well enough, although I also now that chromium oxide (which is what you have on the outside of that bolt) has a galvanic index quite different from aluminium. On some of the frames I made myself, there was certainly some white build-up in the bolt holes, but nothing that was ever worrying. Conversely I could also use good galvanised bolts, and if you look at a galvanic index table that would be the better option, but then it has to be proper galvanised stuff, not the thin stuff that also just rusts some time down the line.
Or… just use the purpose made kit of a good solar mounting solution and be done with it. For the small amount of money saved nowadays, I honestly would not bother with Unistrut anymore. It is a not a bad product, in a pinch it is probably fine, but for new installs I will always prefer a good aluminium rail.
Stainless steel is fine. The surface area of the fasteners is much smaller than the aluminium. As long as the small thing is not the anode, it won’t be a problem (as in the case of stainless fasteners). That is why the renusol fasteners are stainless. If you use galvanized fasteners, they will be the anode which is what you don’t want.
Another thing to note: there is a big difference between different stainless steels in this regard, but I cannot recall the detail. (I vaguely recall 400 series is preferred, but don’t quote me on that)
1 Like
I noticed that Cabstrut have both galvanised as well as stainless spring nuts.
The other way around. 304 is the best stainless steel to get. 430 is the more cheaper option and will be more likely to rust faster and is not recommended for costal areas. There are other grades used for things like acid resistance (316), etc. But the important grades consumers would see are 304 and 430 (cause they make your SS braai out of one of these two metals 
)
Intresting that the cost of SS is determined by the nickel content (the most expensive ingredient) while chrome content of 10.5% or more make it a stainless steel metal. Stainless Steel also do rust(oxidize), but the other metals in SS reacts to oxigen faster that iron so no red iron oxide (FeO). This makes for a self healing material.
2 Likes
So the SS metal we see is an oxide, not the metal itself?
1 Like
Correct, the bit you see is technically Chromium Oxide 
Edit: Similar for most aluminium you work with. That nice matte finish is aluminium oxide.
Missed this, sorry. Won’t touch the stuff. 9/10 when you see photos fo panels blown off a roof - ie. failed mounting structure, it is P2000/unistrut.
There are no good reasons to use something designed for cable routing as a mounting structure.
Purpose made aluminium profile and stainless stell mounting structure is not expensive. Use it.
Their own description:
Unistrut is a “light structural support, often for supporting wiring, plumbing, or mechanical components such as air conditioning or ventilation systems.”
Ps. There are Unistrut ™ products that are designed for PV but they are not galvanised mild steel like we’re use to see in ZA:
1 Like
@warwickchapman what then are you advocating instead?
2 Likes
Bugger, I was looking for ideas to not drill more holes in roof sheets!
Thank you @mmaritz
I didn’t drill as much as I expected…
I measured and removed existing roofing screws for many of the “dowel screws”.
I have a fibre cement roof with wooden trusses. Then only drilled where I had gaps…
I’ve managed to do all my corrugated roof installs using only the holes from existing roof screws. You drill out the hole below to 8mm, and the hole in the metal to 10mm (if I recall) so the seal fits nicely, and then you simply screw in the hanger bolt.