JohnMo Posted June 27, 2023 Share Posted June 27, 2023 PV panels will be circa 60m from house. 2 PV arrays to one inverter. Inverter can be located indoors or outdoors as long as it has a rain cover over it. So question am I better to locate the inverter next to the PV panels and run 3-core 6mm2 armoured cable, to consumer unit? or run DC (4 core armoured) to inverter located near the consumer unit? If DC anyone know what size cable? In both cases the armoured cable will be surface run, except for a short section under a path. Link to comment Share on other sites More sharing options...
TonyT Posted June 27, 2023 Share Posted June 27, 2023 You need to know the string voltages to compare it against the 230 volt cable, this can of course be 2 core to reduce costs and utilise the Swa as an earth conductor Link to comment Share on other sites More sharing options...
JohnMo Posted June 27, 2023 Author Share Posted June 27, 2023 So open circuit voltage is 38.8v and 6 panels per string. So 232.8V Link to comment Share on other sites More sharing options...
SteamyTea Posted June 27, 2023 Share Posted June 27, 2023 Old Mike Lloyd, over at the other place, had his ground mounted array 40 metres or so from his inverter. The DC cabling was standard 4mm. Seem to remember that the voltage drop was not too bad. Link to comment Share on other sites More sharing options...
joth Posted June 28, 2023 Share Posted June 28, 2023 What's your grid supply voltage typically like? If it's on the end bumping 250V you want the inverter as close to CU as possible, otherwise the long AC run can have a voltage rise along it and the inverter cut out on sunny days due to seeing grid overvoltage. A friend had this issue and electrician ended up putting the whole house on a voltage reducing transformer which seems a silly hack to get around this. Link to comment Share on other sites More sharing options...
JohnMo Posted June 28, 2023 Author Share Posted June 28, 2023 Been doing reading up overnight. My AC and DC voltage is about the same. but I have 2x PV strings feeding a single inverter, so the amps on the AC side is double the DC side. Found a voltage drop calculation online https://photovoltaic-software.com/solar-tools/voltage-drop-calculator-dc-ac Have compared the AC and DC voltage drops and power loss. Looks like keeping DC to close to the CU will work best. AC voltage drop 5V Energy loss 90W DC voltage drop 2.5V Energy loss 17W, but 2x strings so 34W 13 minutes ago, joth said: If it's on the end bumping 250V you want the inverter as close to CU as possible Looks like our voltage is in the 240v range, so it makes sense to have the inverter close to the CU for that reason also. So will look to get some 6mm2 4-core SWA cable. Run PV cables into a DC isolator near panels, 6mm2 4-core SWA cable to inverter. AC from inverter to meter, AC isolation switch, CU. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 28, 2023 Share Posted June 28, 2023 I know you are not going MCS, but I think they specify a 1% volt drop. This is because of metering, so may well be a more general rule by DNOs. Link to comment Share on other sites More sharing options...
JohnMo Posted June 28, 2023 Author Share Posted June 28, 2023 DC has a 1.07% voltage drop based on 60m. The AC 2.24%. If I plan the route I may be able to drop a few metres of the length, and drop the DC percentage voltage drop below 1%. Another reason to stay DC for the long run. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 28, 2023 Share Posted June 28, 2023 (edited) 5 minutes ago, JohnMo said: Another reason to stay DC for the long run. Are there any special rules applied to long, exposed, DC runs? Generally considered more dangerous than AC. Maybe a RDCDD fitted (a DC RCD). Edited June 28, 2023 by SteamyTea Link to comment Share on other sites More sharing options...
JohnMo Posted June 28, 2023 Author Share Posted June 28, 2023 15 minutes ago, SteamyTea said: Are there any special rules applied to long, exposed, DC runs? Generally considered more dangerous than AC. Maybe a RDCDD fitted (a DC RCD). Good question, hopefully someone can answer? Link to comment Share on other sites More sharing options...
SteamyTea Posted June 28, 2023 Share Posted June 28, 2023 2 minutes ago, JohnMo said: Good question, hopefully someone can answer? I can't answer it, and a sales person would just say it is not a problem. Link to comment Share on other sites More sharing options...
TonyT Posted June 28, 2023 Share Posted June 28, 2023 (edited) any cable has to withstand the environmental, voltage and current conditions they are expected to operate So if it was my install I might consider ducting below 600mm or a point where impact is reduced, lower if it a field that gets ploughed for example. cable warning tape in layers above duct and suitable signage at ends of cable, armoured cable into appropriate DC isolators. Edited June 28, 2023 by Nickfromwales Typo Link to comment Share on other sites More sharing options...
JohnMo Posted June 29, 2023 Author Share Posted June 29, 2023 Bought some 6mm2 4-core armoured cable have laid that in to place roughly for now. Will run DC for what looks like about 52m from PV DC isolator to the inverter. Ploughs etc have no access as the PV will be located on a very steep hill, with trees to the rear. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 30, 2023 Share Posted June 30, 2023 8 hours ago, JohnMo said: Will run DC for what looks like about 52m from PV DC isolator to the inverter. Was thinking it may be worth having two DC isolators at each end of the DC line, then thought, you switch the AC line off first, so not really necessary. Except, someone that does not know about PV may not think to isolate the DC side, so maybe one near the inverter is sensible. Link to comment Share on other sites More sharing options...
JohnMo Posted July 7, 2023 Author Share Posted July 7, 2023 To finish thread off. Inverter located around 52m from array. 4 core 6mm2 armoured cable used to transmit DC power to inverter. DC isolator located next to the array and DC isolator also on inverter. AC voltage at inverter is around 145 to 146 volt. If I had located the inverter at the array and run the cable in AC, the resulting voltage drop may have resulted in over voltage issues. 1 Link to comment Share on other sites More sharing options...
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