Adam2 Posted November 12, 2021 Share Posted November 12, 2021 Probably not going to install PV now but may in future so thinking to install cables from flat roof to meter room now. What spec cable sighs I install? Will not be a huge setup. Link to comment Share on other sites More sharing options...
Conor Posted November 12, 2021 Share Posted November 12, 2021 (edited) 6mm² DC cables. You need two per string. They need to be labelled as well. Edited November 12, 2021 by Conor 1 Link to comment Share on other sites More sharing options...
ProDave Posted November 12, 2021 Share Posted November 12, 2021 .... Install them in conduit and do something to keep the roof ends out of the weather until needed. Use proper high voltage DC rated cable e.g. https://www.ebay.co.uk/itm/203648797875?hash=item2f6a6a0cb3:g:v6wAAOSwgydhZfAJ That's a random link to show you what you want, not a recommendation to buy from that particular source. 1 Link to comment Share on other sites More sharing options...
joth Posted November 12, 2021 Share Posted November 12, 2021 If the conduit is not entirely visible and labeled, (e.g. if hidden behind plasterboard at all), it should be armoured. 1 Link to comment Share on other sites More sharing options...
TonyT Posted November 12, 2021 Share Posted November 12, 2021 4 or 6mm 2 core swa. Wrap the external cable in amalgamating tape and leave clipped to wall so it’s not damaging roof.( or gland it into a plastic box) leave plenty at either end to allow for a neat termination. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 12, 2021 Share Posted November 12, 2021 2 hours ago, joth said: If the conduit is not entirely visible and labeled, (e.g. if hidden behind plasterboard at all), it should be armoured. We just run 2-core SWA and terminate to the DC singles at each end with rotary isolators. That's just to get a means of converting from cable type to cable type. 1 Link to comment Share on other sites More sharing options...
Adam2 Posted November 12, 2021 Author Share Posted November 12, 2021 Great thanks will run 2 x 6mm cable down to elec room with other cables 80 quid now to save hassle in the future seems good value Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 12, 2021 Share Posted November 12, 2021 9 minutes ago, Adam2 said: Great thanks will run 2 x 6mm cable down to elec room with other cables 80 quid now to save hassle in the future seems good value You cannot just run these DC cables as you wish. These things are the most dangerous cables in the house. Regs, and your insurance ( and any chance of getting a retro-fit PV install signed off ) will rely on you doing this to the letter, photographing it for downstream evidence, and following the rule-book to the letter. Link to comment Share on other sites More sharing options...
TonyT Posted November 13, 2021 Share Posted November 13, 2021 You could say that about any cable though, but running it in SWA, in safe zones protecting cables at timber holes, adding safe plates over cabling will all help, totally agree about the photos for evidence. Link to comment Share on other sites More sharing options...
Adam2 Posted November 13, 2021 Author Share Posted November 13, 2021 OK thanks for the info, I was maybe a bit carefree as in my camper I have a couple of full size panels on the roof and didn't consider the greater power/risk of more panels on the house. 12/24V DC doesn't trigger the same anxiousness as dealing with 240V AC. Why is running this down behind plasterboard riskier than running AC cables the same way - they don't have any extra protection. Will check with my electrician and make sure he's happy with the protection/routing plans anyway. Link to comment Share on other sites More sharing options...
TonyT Posted November 13, 2021 Share Posted November 13, 2021 Quote. MCS installation guide. ’Because PV array cables almost exclusively rely on double or reinforced insulation as their means of shock protection they should not be buried in walls or otherwise hidden in the building structure as mechanical damage would be very difficult to detect and may lead to increase instances of shock and fire risk. Where this cannot be avoided conductors should be suitably protected from mechanical damage, suitable methods may include the use of metallic trunking or conduit or the use of steel wire armoured cable in accordance with BS 7671’ 1 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted November 14, 2021 Share Posted November 14, 2021 12 hours ago, Adam2 said: 12/24V DC doesn't trigger the same anxiousness as dealing with 240V AC With PV you may be dealing with up to 1000V DC. 12 modules in series will often have an open circuit of 530V DC, though it is usual to split that into two. Link to comment Share on other sites More sharing options...
joth Posted November 14, 2021 Share Posted November 14, 2021 18 hours ago, TonyT said: ’Because PV array cables almost exclusively rely on double or reinforced insulation as their means of shock protection In other words, AC has RCDs/RCBOs but PV doesn't. Also PV has higher peak voltage, and even if the sun is hiding, DC can kill at lower voltages anyway. Juicy. Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 14, 2021 Share Posted November 14, 2021 Even in safety zones, I would use additional cation as to where these ( SWA ) cables are run eg to avoid any likelihood of someone hanging up a signed picture of Tony Blair for darts night. Link to comment Share on other sites More sharing options...
Adam2 Posted November 14, 2021 Author Share Posted November 14, 2021 Thanks again, great info which I hadn't seen covered on here before Link to comment Share on other sites More sharing options...
gramos Posted January 11, 2022 Share Posted January 11, 2022 I just came across this thread , thankfully, I am just installing an off grid system for a new house . I tested the output of 7 panel , 4 X strings and all 4 string were producing over 300 volts , total output 1280+ volts , this on a partially sunny day . I have to take this power to the " power station" steel shed so am looking at suitable cable . The highest solar rated cable found is 10 mm2 . Does this cable size have enough capacity for this voltage ? I have tried some if the online converters but there are big variations. Link to comment Share on other sites More sharing options...
joth Posted January 11, 2022 Share Posted January 11, 2022 1 hour ago, gramos said: The highest solar rated cable found is 10 mm2 . Does this cable size have enough capacity for this voltage ? Can't tell, would need the specific product data sheet, as max voltage is as much about the insulation thickness as the conductor area. Cross section area is only useful for gauging max current. I think all PV cable should be good for 300V though? 1000V is typical rating. Link to comment Share on other sites More sharing options...
ProDave Posted January 11, 2022 Share Posted January 11, 2022 2 hours ago, gramos said: I just came across this thread , thankfully, I am just installing an off grid system for a new house . I tested the output of 7 panel , 4 X strings and all 4 string were producing over 300 volts , total output 1280+ volts , this on a partially sunny day . I have to take this power to the " power station" steel shed so am looking at suitable cable . The highest solar rated cable found is 10 mm2 . Does this cable size have enough capacity for this voltage ? I have tried some if the online converters but there are big variations. Be VERY careful, that voltage will kill you and what's worse it will bloody well hurt all the time you are dying. You normally leave at least one panel unplugged so the string is not completed until you have done ALL the DC wiring. Go and unplug one panel off each string before you do any more. As above 4mm or 6mm cable will be fine, make sure what you buy is sold as DC solar PV cable with a voltage rating of at least 1000V it is available in red and black colours. 1 Link to comment Share on other sites More sharing options...
dpmiller Posted January 11, 2022 Share Posted January 11, 2022 what inverter has a 1.5kV input? Surely these strings are going to be separate or series pairs at the most? Link to comment Share on other sites More sharing options...
ProDave Posted January 11, 2022 Share Posted January 11, 2022 I read it as 4 strings. So you will need to take each string individually to the inverter via a DC isolator switch. So that will be 4 lengths of red and 4 lengths of black cable. So each string is 7 panels, and you have 4 of them, that's likely to be an 8kWp system Link to comment Share on other sites More sharing options...
SteamyTea Posted January 11, 2022 Share Posted January 11, 2022 @gramos Are you doing this install yourself? If so, be very careful. PV is, as @ProDave says, deadly. Link to comment Share on other sites More sharing options...
markc Posted January 11, 2022 Share Posted January 11, 2022 50 minutes ago, SteamyTea said: @gramos Are you doing this install yourself? If so, be very careful. PV is, as @ProDave says, deadly. DIY installers often forget PV is the opposite way around to most installs. Guy near me wanted some help … when I said “this thing is live” his response was … no it’s not, it’s not connected to the mains yet ? Link to comment Share on other sites More sharing options...
epsilonGreedy Posted January 11, 2022 Share Posted January 11, 2022 (edited) 2 hours ago, ProDave said: Be VERY careful, that voltage will kill you and what's worse it will bloody well hurt all the time you are dying. Are you a reincarnation of your former self Dave? 2 hours ago, ProDave said: You normally leave at least one panel unplugged so the string is not completed until you have done ALL the DC wiring. Go and unplug one panel off each string before you do any more. Now you tell me. I was hoping to get 3 panels fixed on the roof and electrically terminated in the loft before taking the scaffolding down. Then 6 months later finish off the install adding the inverter and 240v feed into the main CU. Is there a safe way to achieve that? Thinking aloud, could I terminate the raw PV in the attic with a hefty double poll master rotary switch, then 6 months later install everything else before connecting up to the attic double poll switch? Then the final commissioning event would be to throw the master switch in the attic, hence no external roof access is required. Edited January 11, 2022 by epsilonGreedy Link to comment Share on other sites More sharing options...
TonyT Posted January 11, 2022 Share Posted January 11, 2022 A DC rotary isolator in the loft for your install that will be completed at a later date makes perfect sense. Link to comment Share on other sites More sharing options...
gramos Posted January 12, 2022 Share Posted January 12, 2022 On 11/01/2022 at 10:11, joth said: Can't tell, would need the specific product data sheet, as max voltage is as much about the insulation thickness as the conductor area. Cross section area is only useful for gauging max current. I think all PV cable should be good for 300V though? 1000V is typical rating. On 11/01/2022 at 10:11, joth said: this is the cable spec : Rated voltage 1,500 VDC (max. 1,800 VDC) so will be high enough Link to comment Share on other sites More sharing options...
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