DC combiner / Fuse / control box

[Isetech]

I had my first proper whack from DC, which got me thinking.

What is the obejective of installing DC isolators, fuses and surge arrestors in a sperate box.

To protect the soalr panels, the wiring from the solar panels to the MPPT or to protect the inverter.

It cant be to protect the inverter, apparently the inveter has built in protection both surge and overload and a DC isolator on the side of the inverter.

I think people just climbed on the band wagon whern they saw a "DC combiner box" used for large solar installs. The box is used to combine, fuse and isolate many strings.

It is not neccessary for small domestic installations, or is it.

What it taught me, was it creates a false sense of safety while working on the system.

YOu can fit an isolator and fuses thinking if you switch it off and pull the fuse, you could for exapmple work replace the surge arrester, I dare you to try.

If you are going to create this false sense of safe isolation you better make sure you mount a diagram with a safe isolation proceedure.

Mounting a DC isolator in a domestic solar installtion serves no pupose, why because if you swith off the isolator ther could stil lbe power on the bottom of the isolator, unless you remove the fuse there is still power on the surge arrester.

Something you need to consider, MPPT' are bridged in the inverter.

So the only way to safely work on a small Dc box is to make sure you switch off the DC isolator on the side of the inverter.

Hence the reason I beleive these DC boxes being installed are just creating more places for loose connections.

I am still living and learning so feel free to correct me or share your opinion on this topic.

[Isetech]

A separate DC isolator mounted next to the inverter, in case you need to remove the inveter, might not be a bad idea.

[Justloadit]

The purpose of the combiner box is to be able to connect a number of arrays in parallel and then have one wire to the inverter.
As an example you could have 5 arrays of 2 panels which have an open circuit voltage of 104V, and placing 3 PV panels may exceed the Inverter O/C voltage specification.
So in total if each array is 11Amps as an example, then at MPPT would be approximately 84V at 55Amps.

A proper combiner box, should have a suitably selected overload disconnect device on each array to disconnect from the bus.
There are 2 reasons for this,
1. To be able disconnect and service one array if required.
2. To protect one array in the case that it fails for what ever reason, from the full power of the other arrays feeding into the faulty array, the over current should blow the fuse or trip the breaker to isolate the faulty array.
Using the above example, if the one array has a short circuited cell, which can happen due to over heating, then that specific array voltage would be lower than the other 4 arrays. This would cause the other 4 arrays to directly feed into the faulty array, causing 44Amps to flow into the faulty array at midday. This extended over current, would cause the faulty array to heat and might possibly cause a fire.

[Isetech]

I understand how a DC combiner box works and why I would install one in a large installtion with many strings.

My concern is for the domestic units being installed in homes with 2 strings or 4 strings. The ones which dont serve the purpose of a "combiner box" but rather just an extra cost to the installtion.

Some people havent read the equipment manuls and are not aware that the equipment has the safety features built in.

Some might say its a nice to have feature, with the budgets getting tighter and tighter, we need to find ways to drop the equip cost t oan absolute minimum. YOu can get a full 5 kva solar system with panels and a COC for around R100k

[Thys LOW Elektries]

In the land of the blind, the man with one eye is king!
The problem is most installations are done by unqualified people with very little to no knowledge of electricity.
I had been to a house with a combiner box that had no spd, and only fuses. The combiner box was bought online, very cheap, and from a reputable dealer.
I am pretty sure that the box has a purpose somewhere but protecting three strings of pv panels, I doubt.
People must stop watching YouTube and stop looking for cheap stuff on the internet.
If you buy something make sure that you do you your homework and make sure whatever you buy will be able to do what it is supposed to do

[Isetech]

It goes both ways, some solar installers have a much better understanding of how solar sytems work and electrcians a better understanding of the electrical industry (not when you look at COC's).

I dont believe elctricians should be doing solar installations without some form of official training and certification.

The same with solar installers, they should have some form of elctrical training and certification.

It is sad that we have been forced into this situation creating a dangerous environments for the public.

The bottom line is we need to "all" get togetehr thrasdh this out until a standard and set of regualtions are published, until then its going to be a free for all. The only people who are going to suffer is the public (they always get the short end of the stick).

People in the renwable indsutry are smiling all the way to the bank.

Load shedding stages go up and the smile gets wider, you see the importer posting pics of new sports cars, they are printing money. If you climbed on this gravy train in June last years, if you havent increased your turnover by 10X, you doing something wrong.

It is good to see other people have realised the opportunity and starting to import, stuff like solar panels. At tleast now we dont have to wait for tier 1 panels, they are availbe by the container load.

IF are waiting for solar panels, shop around there are containerr loads of panels arriving.

As with everything beware of grey market products, I hear people are importing solar equipent directly to SA, I dont know if these panels are from the supplier or just not going via the registered importer.

[GCE]

Be careful of just buying panels because they are available from some or other outlet that you do not know.

When the panels do not produce what they should be producing you could end up having to replace at your cost

Even simply things like transportation and handle by suppliers in there warehouse is important if you don't want to end up with hairline cracks coming back down the line to bite you