PV wires - unequal lengths?

[Joeboy]

Masking tape, single wrapped and join as a tab and use a sharpie, works for me. Surprisingly resilient.

[marshman]

All useful suggestions for the future, none of which answer sunrisemikes question

As to "schematics" left by the installer at best they will only tell you if there were one or two strings - i.e. the arrangement of the panels, they will not identify individual cables or their routes up o to the roof.

SO back to the O.P. dilemma.

First you need to go look at where you PV feeds into the DC switch and the inverter. Determine if there are 1 or 2 strings, i.e. how many cables run back tot he switch(s) and the inverter?

Secondly, are all the panels facing the same way in the same orientation? Are the 4 you left in place on a different part of the roof facing a different direction, if so they are likely a separate "string".

You are not clear where the 2 long and 2 short cables come from. Do they all run back to the inverter or do only 2 go back to the inverter and the other two go to the four "unmoved" panels?

I assume the four cables all have the connectors still attached?

You say you have 16 panels so I would assume they were arranged as 2 strings of 8 panels.

I would suspect, but you need to check this, that one of the four wires goes to one "end" of the four unmoved panels. The other three cables will run back to the inverter. Unfortunately you need to do some detective work to identify which cable is which, as there should be one cable from the other end of the four already running back to one of the DC switches (assuming you have 2 - which also means 2 strings).

Without more information it is difficult to give you guidance on how to identify which cable is which.

As a first attempt you could do the following: (assuming it was originally wired as 2 strings of 8 panels)

1. Ensure ALL DC Switches are OFF.
2. Remove the covers of the switches to give access to the terminals.
3. On the roof use a voltmeter to check for any voltage between ANY of the four cables - be careful as with 4 panels still connected there could be around 160V DC on them.
4. I suspect you will not find any voltage, if this is the case then proceed.
5. The connectors are polarised so hopefully you have 2 +ve and 2 -ve. Connect one of the +ve cables to one of the -ve cables.
6. Check on the terminals of the DC switches for a voltage (needs to be daylight - no need for it to be sunny)
7. If you get around 150V then you have successfully identified the cables for one string, the one connected to the four unmoved panels - the other two will be for the other string. If not go back on the roof and disconnect the +ve cable and connect to the other -ve cable and try again. If still no good you know that +ve cable goes to one end of the panels you removed. So mark it and then try the other +ve cable. connecting to the first -ve one. Check for voltage again, if there is a voltage those two cables are for the string with the unmoved panels and the other -ve goes with the first +ve that you marked for the other string. If not then as a final check connect the second +ve to the second -ve and check voltage, you should get something this time. If not then there is something else going on and the wiring is not as I have assumed. If there is a voltage then the two cables that are connected are for string 2 and the other two are for string 1.
8. So now fit 4 panels and connect them together and connect the "end cables" to the two identified as the second string (these couple to the four unused panels)
9. check for voltage on the DC switch - you should now have around 300V on the terminals - BE CAREFUL THIS IS A LETHAL DC VOLTAGE!
10. now fit the other 8 and connect their "end"s to the other two cables. Check for a similar voltage on the other DC switch.
11. If all seems OK DOUBLE CHECK THAT THE POLARITY IS CORRECT, i.e. POSITIVE is actually POSITIVE - follow the wire to the inverter. It should be as the connectors are polarised, but it is easy to check and expensive (new inverter) if it is wrong!
12. Replace the covers on the DC Switches, turn on the DC then turn on the AC and all should be well.

DISCLAIMER !!!! I have made a lot of assumptions about your set up and if you don't feel competent at checking voltages safely don't do it and get someone in - DC at the levels from PV panels is lethal - doubly so if you get a shock whilst on the roof!

[Fintray]

Hi Marshman, that's a detailed reply but how does that help the OP?

[Mr Gus]

if there are schematics / sign off papers by a firm or individual there may well be an installers name to google & ask directly.
my mate remembers jobs from decades past because even in. duplicate housing the electrics are not necessarily identical from new, & certainly not maybe a decade on, the recall was less him & more the trade in general I always thought.

& some people go the extra mile in anticipation of further work down the line, ..welcome conscientious planning.

You never know till you pull out the manual, ..which many don't read

[Joeboy]

Talking about unequal length of wires, I have a conundrum at the moment. We had to take 12 of the panels off of the roof to renew the felt, and re slate. The other four are on another part of the roof. I turned off the a/c and D/C switches and the roofer removed the panels. After reinstating them, neither he or I can figure out how they are wired up. There are two long leads and two short ones. I am guessing that four of the panels are linked to the other 4. Any ideas how they could be wired up? Any advise will be gratefully received!!
Here's a photo, the other 4 are on the lower roof out of shot just to the right.

Mike

I can't see the photo but as a start you could look at the four existing panels and how they are wired along with their operating parameters and be able to extrapolate a scenario for all 16 which falls within the inverter operating limits. Do a line drawing of what you know, get a multimeter and check polarity on the known cables (and MARK THEM UP). If this is outwith your skill to work out (not embarrassing if it is),pay someone to come in and do it and don't make the same mistake again. I'm betting two strings of 8 but don't bet your health on it. Defo learn from this.

[marshman]

Hi Marshman, that's a detailed reply but how does that help the OP?

I was replying to sunrisemikes question further down - have edited my post as I said OP when I meant sunrisemikes question in post 4.

[Fintray]

Hi Marshman, that's a detailed reply but how does that help the OP?

I was replying to sunrisemikes question further down - have edited my post as I said OP when I meant sunrisemikes question in post 4.

I know Marshman, just having a bit of fun, but that's the problem in most forums is that the original question often ends up bearing little resemblance to the answers as thread grows.
P.S. As this reply shows!

[John_S]

Sunrisemike

I found this topic

https://camelot-forum.co.uk/phpBB3/view ... 881#p25881

and your post

We are off grid and registered our panels with edf 10 years ago. I think we were the first, as they demanded wiring diagrams etc before agreeing to accept our install. I have a dc voltage monitor that opens ac circuits at different voltages. As the batteries go into absorb, it switches on one dehumidifier, then another and finally the off peak heater. This keeps the meter whizzing, even with charged batteries.

mike

Do we presume that you don't still have the wiring diagrams etc that you provided to EDF? If you have lost them, perhaps try asking EDF for a copy. If you ask them for a copy of all the data that they hold on you, they would be obliged to send you it if they still have it.

[AGT]

To the OP, it won’t matter.
Think of the panels on the roof numbered 1-8.
One end will have a negative, one end will have the positive back to the inverter no need to worry about keeping them equal lengths.

Marking cables makes it easy for future maintenance, especially when so called professionals turn up and pull things out without marking cables, makes life easier so I’m all for that.

You can use masking tape, coloured tape with different number of bands of tape, critchley markers, whatever you want just make sure you can identify pairs
Good luck