January 30, 20233 yr Hi All I had an issue where half my panels were not generating anything at all. Original installer couldn’t come in so I had my electrician take a look. He sorted out the issue but also pointed out that the original installer had used 1mm cabling from the panels to the DB when it should rather be 4mm. Can anyone advise me around this?
January 30, 20233 yr 3 hours ago, JK844 said: Hi All I had an issue where half my panels were not generating anything at all. Original installer couldn’t come in so I had my electrician take a look. He sorted out the issue but also pointed out that the original installer had used 1mm cabling from the panels to the DB when it should rather be 4mm. Can anyone advise me around this? Wires need to be correctly sized for the current and voltages used in your system. You did not mention this information in your post making it difficult to answer. In any event, I do not see many scenarios where the 1mm2 cable will be sufficient. Also remember that PV cables are moisture, sunlight, and flame-resistant and behave extremely well in very hot temperatures. Undersized cables are a major fire risk.
January 31, 20233 yr I was told minimum 4mm square wire over short distances and recommended was 6mm square.
January 31, 20233 yr 18 hours ago, JK844 said: Can anyone advise me around this? also @I84RiS, @Chris_S and @razzor13bt the cable diameter is tied to the amount of current that is supposed to be supported, 4mm^2 for a 6m run at 28Ampere is generally considered fine for DC 250V tension, that would be 250 * 28 = 7kWp since the panels would not neccesarily produce that current and voltage constantly, with MPPT in play the voltage may float up and down and the current is what one takes for specifying the cable, should drop from 28A as this should be the Isc or short circuit current of the deployed panels... So, the above example is for a high voltage MPPT inverter, if your inverter is the low voltage type and you run, let's say 100V and thus 2.5 * 28 Ampere for 70 Ampere to also end up with 7kWp, then the cabling for a 6m run should really be closer to 70mm^2... Note the cabling diameters specified are to keep losses at a minimum no more than a 2V drop out of 250V and 100V in each case over the distance, which is nuts, no-one would cable things up with this size cable, unless funds were not an issue, if you look at this page and look at the table as snipped and pasted below you will see that the 1x4.0 is rated at 55Ampere, but resistance/length play a role and not mentioned here is temperature, which also impact the conductors resistance... colder is betterer and warmer... maybe 60+°C in places where the sun lights up a cable directly or the coduit it may be running in will increase the resistance of the cable and thus increase the losses in the system... Edited January 31, 20233 yr by Kalahari Meerkat
January 31, 20233 yr Exactly. The higher the voltage the thinner the cable can be. 8 x 550W panels in series can even use 2.5mm2 cable. 4mm is plenty
January 31, 20233 yr 2 hours ago, Kalahari Meerkat said: also @I84RiS, @Chris_S and @razzor13bt the cable diameter is tied to the amount of current that is supposed to be supported, 4mm^2 for a 6m run at 28Ampere is generally considered fine for DC 250V tension, that would be 250 * 28 = 7kWp since the panels would not neccesarily produce that current and voltage constantly, with MPPT in play the voltage may float up and down and the current is what one takes for specifying the cable, should drop from 28A as this should be the Isc or short circuit current of the deployed panels... So, the above example is for a high voltage MPPT inverter, if your inverter is the low voltage type and you run, let's say 100V and thus 2.5 * 28 Ampere for 70 Ampere to also end up with 7kWp, then the cabling for a 6m run should really be closer to 70mm^2... Note the cabling diameters specified are to keep losses at a minimum no more than a 2V drop out of 250V and 100V in each case over the distance, which is nuts, no-one would cable things up with this size cable, unless funds were not an issue, if you look at this page and look at the table as snipped and pasted below you will see that the 1x4.0 is rated at 55Ampere, but resistance/length play a role and not mentioned here is temperature, which also impact the conductors resistance... colder is betterer and warmer... maybe 60+°C in places where the sun lights up a cable directly or the coduit it may be running in will increase the resistance of the cable and thus increase the losses in the system... Regarding temp of cable on a flat roof. I know people use steel conduit outdoors but I'm thinking pvc would be better for less heat. PVC should be fine for a 4 meter outdoor section right?
January 31, 20233 yr 6 minutes ago, Chris_S said: Regarding temp of cable on a flat roof. I know people use steel conduit outdoors but I'm thinking pvc would be better for less heat. PVC should be fine for a 4 meter outdoor section right? well, if you have lightning in the area, using a steel conduit will lessen the potentially induced energy from a nearby strike, whereas plastic won't give you any benefit in this regard... how about metal within a large plastic conduit to try and keep the temperature down? I'm running my ground mounted panels' power cables in a 32mm PVC irrigation pipe which is about 30cm below ground. (And yes, its supposed to be different and this was/is a temporary installation which will change in the (hopefully) no too distant future.)
January 31, 20233 yr PVC will not last over time. There is a reason the SANS 10142 dictates Metal or galvanised conduit. The Solar PV Array is designed to last 25 years. PVC does not have such life especially in the high UV conditions & elements. There is method to the madness. I know it's expensive & it's not pleasant to work with but it's a product that lasts.
February 2, 20233 yr On 2023/01/31 at 9:33 PM, Steve87 said: PVC will not last over time. There is a reason the SANS 10142 dictates Metal or galvanised conduit. The Solar PV Array is designed to last 25 years. PVC does not have such life especially in the high UV conditions & elements. There is method to the madness. I know it's expensive & it's not pleasant to work with but it's a product that lasts. What's the easiest way for me to go about this. If I use galvanised pipe I'll have to buy a pipe bender right or can it be bent with a spring like pvc?
February 2, 20233 yr It has Bosal connectors, couplers & 90° bends designed for cables exactly the same as the PVC conduit. No bender required. You cut it with a hacksaw. It's actually just hard to work with as it gets sharp edges & gloves are a very good idea.
February 9, 20233 yr On 2023/02/02 at 7:04 AM, Steve87 said: It has Bosal connectors, couplers & 90° bends designed for cables exactly the same as the PVC conduit. No bender required. You cut it with a hacksaw. It's actually just hard to work with as it gets sharp edges & gloves are a very good idea. Steve, how are you sealing the bosal connecter to prevent water getting in the pipes? Silicone?
February 9, 20233 yr You could very well use Silicon sealer yes. PVC weld is used on the PVC pipes so something similar definitely would also work well
February 9, 20233 yr I can tell you something else that will be very necessary when working with this Bosal pipe. You will need to fish the cables with Fish tape & also use gloves. These pipes can rip your fingers in minutes & wires need the fishtape it's a must.
February 10, 20233 yr 13 hours ago, Steve87 said: I can tell you something else that will be very necessary when working with this Bosal pipe. You will need to fish the cables with Fish tape & also use gloves. These pipes can rip your fingers in minutes & wires need the fishtape it's a must. How well does the fish tape push through the 90 degree bends?
February 10, 20233 yr It depends on the length of the pipe and the number of bends. Normally if you use the short bend you won't be able to pass more than one bend. You can always install bends that have inspection covers. When using the long bend it is possible to pass a few.
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