I have been looking at a couple of my friend’s combiner box installations and have noticed wiring differences between them. Further to this I have searched online and found a number of pictures where the wiring is also different (see pictures below).

This has made me question what the correct way would be to wire a combiner box and if there is a set standard?

So, what is the correct way?

From what I can make out through numerous searches, one solution is for your incoming positive & negative wires (from the solar panels) to each go into a Fuse Holder and then into the top of an isolator which doubles up into your SPD. The bottom of your Isolator then goes to your Inverter - I have posted a stick drawing of this below as Option 1 and an alternative as Option 2.

Are any of these correct and if not, what would be the better/preferred way?

 

Note: The hardware (fuses, Isolator & SPD) is also very different between installations - I have posted these questions under a different thread: https://powerforum.co.za/topic/24599-how-to-correctly-size-solar-combiner-box-components-fuses-isolators-spd%E2%80%99s/

 

Ok, I'll bite...

Option 1 seems the correct one, but...

if you are going to turn off the isolator manually, when T&L comes around and for the duration keep the panels disconnected from the inverter, then Option 2 seems like the betterer candidate, I reckon...

What about a third option?

Option 3: Panels -> Isolator -> Fuses -> SPD

Isolator to switch off to work on fuses / SPD

Fuses before SPD to blow if a surge is suppressed by the SPD

On the older low voltage MPPT inverters, where string were paralleled, I have seen: Panels-> Fuses on each string of panels-> combined into a single SPD -> isolator -> inverter

(I believe having the fuse first was to protect when combining strings if one string were to go short circuit, the fuse would blow because of the combined current of the other strings)

1 hour ago, JacquesVDM said:

What about a third option?

Option 3: Panels -> Isolator -> Fuses -> SPD

Isolator to switch off to work on fuses / SPD

Fuses before SPD to blow if a surge is suppressed by the SPD

100% logic, and when lightning is present, by isolating the fuses and SPD's, nothing can be blown up. Option 1 your fuses and SPD's can be blown by lightning.

Edited November 16, 20232 yr by TimCam

Just some clarification on the terminology use as"Isolator". Dc Mcb should be used as an Isolator. Isolator can not be opened under load, but an Mcb could. In one of the above pictures the Noark Mcb has a ka rating of 15KA so it can safely isolate the solar array under load.            Panels→Mcb→Fuses→Spd

 

Interesting question, I see the following as the safest:

PV -> Fuses -> Isolator -> Inverter

The SPD is in parallel so it doesn't fit into the chain here, but should hang off before the isolator. Otherwise if you turn off the isolator you then remove over voltage protection.

The fuses should also be on the PV side of the isolator for the same reason, otherwise you remove over current protection if you isolate the panels.

 

 

I recently managed to obtain a Solar CoC for "my" solar installation which consists of 8kw Deye Inverter, 24 x Canadian panels (10360w) and 2 x Dyness 5.2kwh batteries and have attached the pictures of my Combiner Box as reference.

In this installation, as can be seen in the picture of my combiner box, I have 3 strings. 2 of the strings are paralleled at the inverter (MPPT1) and 1 string is on its own (MPPT2). Each of the strings have their own fuses (x2), a No-Ark MCB (and SPD).

For my installation, each wire from the solar panels (positive & negative) goes through their own separate fuse (entry at bottom of fuse), which then go to an MCB (isolator) and doubles to an SPD.

From the bottom of the MCB, the wires go to the inverter with 2 strings going to MPPT1 (paralleled at the inverter) and the 3rd string going to MPPT2.

An interesting point (relating to combiner boxes) that has come to light, through the process of my recently obtaining a Solar CoC (Dec 2023), is that within the Combiner Box, you need to fit Bootlace Ferrules at the end of each Solar wire (stranded wire). This is required for both single wires (single wire bootlace ferrule) and where 2 wires are going into a MCB (twin wire bootlace ferrule).

A CoC discussion can be found here:

 

@Marcodp just one question?  from your picture I can see the AC incomer and output cables are 6 mm2 is that ok for 8 KVA 

@Antonio de Sa, you have a good eye - it is 6mm which is incorrect ....it must be changed to 10mm.

The original install was a 5kva and was later upgraded to 8kva but the wire was not upgraded at the time so must be re-done which is such a huge irritation 😞 - in the interim the 6mm cable is being protected by a 32A MCB.

Without a doubt, the Deye/Sunsynk 8kva requires 10mm Cable as the inverter spec has a max AC output current of 38.3Aa.c with a continuous passthrough of 50Aa.c.

Edited January 5, 20242 yr by Marcodp

14 minutes ago, Marcodp said:

@Antonio de Sa, you have a good eye - it is 6mm which is incorrect ....it must be changed to 10mm.

The original install was a 5kva and was later upgraded to 8kva but the wire was not upgraded at the time so must be re-done which is such a huge irritation 😞 - in the interim the 6mm cable is being protected by a 32A MCB.

Without a doubt, 8kva requires 10mm Cable ...

@Marcodp why not run another 2 X  6 mm2 surfix and connect in parallel? that should work, I see there stil enough place in the DB to install extra glands. 

Thanks @Antonio de Sa - that would be an option although I already have the 10mm cable 🙂 - just need the time to actually do the work 🙂 

Your sharp eye caught me out before I got the chance 🙂 

37 minutes ago, Antonio de Sa said:

@Marcodp why not run another 2 X  6 mm2 surfix and connect in parallel? that should work, I see there stil enough place in the DB to install extra glands. 

The 6mm can be directly out of the manual for a 8kW. I was pointed this out when I indicated this to be 10sq mm. Luckily the person accepted my size and duly changed it straight away. 

I would also add a 2nd one unless the inverter is very close to the main DB. 

45 minutes ago, Scorp007 said:

The 6mm can be directly out of the manual for a 8kW. I was pointed this out when I indicated this to be 10sq mm. Luckily the person accepted my size and duly changed it straight away. 

I would also add a 2nd one unless the inverter is very close to the main DB. 

@Scorp007 That is what years of professionals at work do to you, just a glance you see immediately the shortcomings. However, nice and very professional work. I've also used bootlace ferrules in my installation. 

53 minutes ago, Antonio de Sa said:

@Scorp007 That is what years of professionals at work do to you, just a glance you see immediately the shortcomings. However, nice and very professional work. I've also used bootlace ferrules in my installation. 

Yes but also being in the industry you have some sizes of cables and their currents hidden in a volatile memory 😀😀😀

7 hours ago, Marcodp said:

@Antonio de Sa, you have a good eye - it is 6mm which is incorrect ....it must be changed to 10mm.

The original install was a 5kva and was later upgraded to 8kva but the wire was not upgraded at the time so must be re-done which is such a huge irritation 😞 - in the interim the 6mm cable is being protected by a 32A MCB.

Without a doubt, the Deye/Sunsynk 8kva requires 10mm Cable as the inverter spec has a max AC output current of 38.3Aa.c with a continuous passthrough of 50Aa.c.

I found with my 8.8 kW SunSynk even with 10mm cables, if I run between 8 kW to 11 kW in pass-through the 10mm heated up even to touch. All my main DB's are now running 16mm, except out-houses and generator. 16 mm is a real pain to work with though.🤔

6 hours ago, TimCam said:

I found with my 8.8 kW SunSynk even with 10mm cables, if I run between 8 kW to 11 kW in pass-through the 10mm heated up even to touch. All my main DB's are now running 16mm, except out-houses and generator. 16 mm is a real pain to work with though.🤔

Just saying .....

6mm PV wire rated at 71 A

Nice and soft.

Use bootlace ferrules.

The origin of using 6mm house wire cable for AC output on a 8kW inverter can perhaps be found in the Deye manual. They quote it up to 12kW as per below. 

@Marcodpthis is what I call Solar Porn. What a beautiful installation & well labelled. Makes the next technicians job so easy & nothing is left to the imagination. 

I haven't read the entire thread but this labelling of cables is magic & tells of a person with pride in their work.

12 hours ago, Steve87 said:

@Marcodpthis is what I call Solar Porn. What a beautiful installation & well labelled. Makes the next technicians job so easy & nothing is left to the imagination. 

I haven't read the entire thread but this labelling of cables is magic & tells of a person with pride in their work.

Yes, labels are great for the next tech, but even for yourself in a years time. Makes life so easy for upgrading or fault finding.. 👍

20 hours ago, Steve87 said:

@Marcodpthis is what I call Solar Porn. What a beautiful installation & well labelled. Makes the next technicians job so easy & nothing is left to the imagination. 

I haven't read the entire thread but this labelling of cables is magic & tells of a person with pride in their work.

@Steve87 I fully agree.

The only 2 things I would have done differently,

1. Installing rubber grommets/glands between the trunking and the combiner box.

2. Remove the earths on the Grid and Load connections and go for the Neutral/Earth bond relay. 

Edited January 7, 20242 yr by Virwat

I am also in favour of the relay bond & not the permanent kind. It's been beaten to death on so many platforms, have something in place, don't let the neutral float dangerously. 

Edited January 7, 20242 yr by Steve87

@Steve87 and @Virwat, for clarity and learning, could you elaborate on the Neutral/Earth bond relay ...what it is/looks like and how one would connect this? (Pictures would also help) ?

 

Edited January 7, 20242 yr by Marcodp

Here is a link on the downloads section of the forum: 

 

In a nutshell, the Deye & Sunsynks do not tie the Load Neutral to Earth when in off grid mode. The Kodaks & Axperts use a relay to accomplish this internally built in. Why is this so imperative? Because your homes DB as supplied from Eskom has the Neutral tied to Earth not inside your DB physically but at a designated point further upstream in the network be it at mini sub or street level. This is why an E/L or RCD will trip in the event of a leakage detected. The Sunsynk allows this Earth Neutral bond when the Grid is present, however, when it loadsheds that bond is gone because the Inverter islands (Goes Off Grid & separates from the Grid). 

This makes your E/L or RCD useless. The press to test is no way to test it's operation, you must use a plug tester & if used without a permanent or temporary bonding of the Load Neutral to Earth during Islanding you will find the E/L RCD does not trip. Making for a potentially dangerous outcome if you have a fault. 

@Marcodp Also read through this whole thread. Lots of useful information and opinions.