Best PV panel cables and connectors to use for replacing existing?

ThisIsWeird

Possibly a long shot, but there may be a PV fellow on here? (I asked on a dedicated electrician's forum with a PV section - no reply...)

I've had zero Riso for a while, so I'm going to replace all the external connectors on our ~12-year old panels. Fortunately they are on a garage roof with a high bank beside it, so access should be straight-forward. I also know to be wary of generated DC voltages...

Anyhoo, the Q is - what are the best connectors and cables to use for longevity?

Another Q - why are there two (different) connectors currently on them?!

Oh, and, are these twin-core cables, or are there two separate single-core cables going to each panel?! (Forgot to look)

Thanks.

QrizB

The connector pair in the foreground is a MC4. These are the standard and have been for at least a decade.
https://en.wikipedia.org/wiki/MC4_connector

The connector in the background is less clear. They don't look like the Tyco Solarlok that was fitted to my old panels but more like a straight cable extender? Do you know the make and model of the panel? The manufacturer's data sheet might be Googleable and should tell you the connectors they were fitted with at the factory.

To the best of my knowledge, the only connectors anyone uses for large solar panels these days (from a single rooftop panel to a 50MW solar farm) is the MC4 connector.

Cables are single core and manufactured to a specific EN standard. Common sizes are 4 sq. mm. and 6 sq. mm. 4 is likely to be adequate for a domestic installation (usually rated to at least 1000 volts and 55 amps). This sort of thing:
https://www.elandcables.com/cables/photovoltaic-solar-h1z2z2-k-cable

(Eland are a cable manufacturer. Other brands are available.)

There are people who will sell you a cable, of the length you request (generally up to 100m), already terminated with MC4 connectors. This is not entirely convenient if you need to poke the cable through a hole in eg. a wall, so the other option is to buy the cable and connectors yourself plus a MC4 crimp tool, eg:
https://www.sunstore.co.uk/product/solar-cable-mc4-tool-kit/

I've done this myself for hobby purposes and it's quite straightforward once you get the hang of it!

Edit to add:

I tried to take a photo of the markings on my cable, but it doesn't want to photograph. It's marked "Synergy Solarflex PV1-F 4.0mm 600/1000V". PV1-F is, I think, the DIN standard for solar PV cables; there's also EN50618 which is similar and seems more recent.

ThisIsWeird

That is terrific info - thank you :-)

I'll have a look for the bumph that came with the install - I'm sure the panel make and type is on there.

Interesting - so the cables are single, so there's a + and a -ve? How are they ID'd? And can the MC4s be labelled/ID'd like that too?

Yes, the further-away connector is smaller. I wonder why they'd leave that there instead of cutting the cable and crimping it directly into the MC4?

QrizB

ThisIsWeird said:

Interesting - so the cables are single, so there's a + and a -ve? How are they ID'd? And can the MC4s be labelled/ID'd like that too?

You can buy solar-rated cable with red and black sheaths, but most people don't bother and just use black for everything. Black has the advantage of being more resistant to the sun (although all solar-rated cable should be adequate in this regard).

As foir MC4 connectors, terminology is not straightforward (photo from Wikipedia):

The one on the left (that looks male, and has the red o-ring) is the female connector, and the one on the right (that looks female) is the male connector.

You can see the positive and negative labelling on the picture; this is from the perspective of the solar panel, ie. the panel positive will have the female connector, the panel negative will have the male connector. This will continue be the case when you get to your inverter, with the incoming positive cable having a female connector and plugging into a male terminal on the inverter.

There's a blog here that goes into detail about how MC4 connectors go together:
https://offgridham.com/2016/03/introduction-mc4-connectors/

*** Do check your panels! *** If they weren't fitted withn MC4 connectors from the factory, it's possible (though unlikely) that the installer got them back-to-front. It should be obvious but, if not, check the panel polarities individually with a voltmeter.

Final point: MC4 connectors are not designed to make/break circuits while under load. Make sure your DC switch is off (or wait until nightfall!) before connecting or disconnecting them.

Chris_Type_R

Personally I'd be looking to cut off the old connectors and replace with new MC4s. The tool to make them up is not expensive and relatively easy to use. As above, use a meter to confirm polarity. 

I purchased clips to help with cable management recently ( https://www.amazon.co.uk/dp/B0B21KY7Y4 ) which work well. I'd think that cable tying them to the frame, clipping to the panels would remove the risk of water ingress/chafing. 

I purchased this starter kit which seems to work well enough ( https://www.amazon.co.uk/gp/product/B07Q3TV4XQ/ ), paired with this cable stripper ( https://www.amazon.co.uk/gp/product/B07VN5CNP9/ )

Heedtheadvice

....

and why do you want to replace your cables?

ThisIsWeird

QrizB said:

Do you know the make and model of the panel? The manufacturer's data sheet might be Googleable and should tell you the connectors they were fitted with at the factory.

Panels are Suntech Pluto 200W. I'll do some research. The info that came with it suggests it has a junction box on it, but I don't know if they are openable.

ThisIsWeird

Chris_Type_R said:

Personally I'd be looking to cut off the old connectors and replace with new MC4s. The tool to make them up is not expensive and relatively easy to use. As above, use a meter to confirm polarity. 

I purchased clips to help with cable management recently ( https://www.amazon.co.uk/dp/B0B21KY7Y4 ) which work well. I'd think that cable tying them to the frame, clipping to the panels would remove the risk of water ingress/chafing. 

I purchased this starter kit which seems to work well enough ( https://www.amazon.co.uk/gp/product/B07Q3TV4XQ/ ), paired with this cable stripper ( https://www.amazon.co.uk/gp/product/B07VN5CNP9/ )

Very helpful info - thank you.

ThisIsWeird

Heedtheadvice said:

....

and why do you want to replace your cables?

Long story short - I've been having 'low Risos' for a couple of years, almost always after heavy rain and wind. So I've suspected that some connections were less than perfect.

My Aurora Power One then developed the common EO31 fault, so I duly sent off for a set of relays. Two soldering irons later, and a lifted PCB track, I managed to replace them - wasn't aware that the tracks on each side were joined via some of the relays PCB holes   

Anyhoo, finished the repair, and tentatively replaced it - only to find '0Meg' Riso showing on both arrays. I obviously put this down to a bodged repair of mine, so ordered a professionally-refurb'ed replacement from a reputable company. This initially appeared to work, but the next time I booted it up it, too, returned '0Meg' Riso. So, the one I repaired might be ok after all - IF it's the panels that are being Riso'd.

Since I can get to the panels quite easily myself, my plan was to take them all down and redo all the connectors - there was always some historic Riso issue in any case, so I think it's worth doing. This should also discount the Riso from the inverter issue.

Solarchaser

I run 3 of those aurora/power one /abb inverters and around a year and a half ago I had low Resistance (riso) reported also.
On this occasion my relays were fine.
I took each panel in the array off, cut off their mc4 connectors.... 1 at at time so I was replacing male with male and female with female... and replaced with new mc4 connectors, put it all back together and all has been good since. 

As QrizB has said, make sure your DC switch is off, or it's dark to ensure no shock potential, and just work methodically. 
Once you get into the rhythm of it, it doesn't take too long, however at some point you will put a male crimp on when you meant to do a female, or vice versa, (perhaps several times, quite frustratingly) so if you need 10 sets, id buy 15 or so, to give yourself room for making mistakes without ruining your day.

I bought mc4 crimping pliers, mc4 connectors and 4mm cable from ebay for I think about £40.
I'd expect to pay maybe £50 now with the brexit and cost of living bump.

I should say I bought cable due to wanting to move my inverter.... which I still haven't done, bit it was useful for bypassing individual panels to check if they were the cause... eventually though I figured I'd just replace all connectors for piece of mind.

ThisIsWeird

That's really useful info, Solarchaser - a practical example!

So, the +ve and -ve are usually ID'd by having the male and female ends on the PV cables? Lawdie. Why don't they have bludy proper labelling!

To clarify, I didn't replace the relays due to Riso, but due to the well-known EO31 fault and, sure enough, one relay had a completely burned-out pin. Although I've had a dodgy Riso issue for a good while - which I could get around by leaving the 'dodgy' array disconnected whilst the Aurora booted up, and then I could switch in the second without issue - the new 0Meg Riso issue appeared, seemingly by annoying coincidence, after I replaced the inverter.

A warning to anyone carrying out relay replacements - some of the relay pads are joined to the other side of the PCB by electrical 'tubes', so to release the relays requires enough heat to melt the solder on both sides of the PCB, but not so much that the pads and tracks lift. As part of my bodge, I pulled a still-attached 'tube' out with one relay, and lifted a couple of other tracks... I had to run bridging wires through the PCB hole to make good - it became a 'mare, and I am used to soldering.