camelot-forum.co.uk

Hi Gents.
We have some upcoming projects this summer to extend our solar capability.

The larger arrays will go through the sunsynk mppts just fine,

But we are planning 2 strings, which would not hit the start up voltage and even if could, would be woefully inefficient if run through the sunsynk.
As a result ive bought a 45A Victron SmartSolar 150-45 -150 Voc, PV Charge Controller to run these strings with.
But i will need a solar disconnect, especially as the cables will be underground for 10m (planned swa)

As space is a precious commodity, i was thinking about a 2 string isolator, but i am just coming up confused with what will do the job

Strings will be 3 panels of 440W.
Voc 38.9V so 38.9x3, x1.2 = 140.04V
Isc 14.31A so 14.31x 1.25 = 17. 89A

So i am looking for something that can handle 18A or 20A and 150V per string.

Some 4 pole switches ive looked at last night have a 20A rating, but their specs say only do a max of 8A per string, which suggests the max Amps is split between the two strings evenly with some buffer room

Another ive looked at is 25A and does 18A per string, which clearly is not splitting the main number evenly between the two, but suggests the strings are both able to take the max amperage.

And the majority just have a table that doesnt make clear if the values are per string or not.

Can anyone help?

Some good info

https://niceic.com/newsletter/connectio ... isolators/

With a tight space, I would use a pair of these (one for neg, one for pos) for each string. Could just mount a piece of DIN rail, or use an enclosure.

https://cpc.farnell.com/mersen-ferraz-s ... dp/FF04040

jonc_uk wrote: ↑Sun Apr 13, 2025 1:43 pm With a tight space, I would use a pair of these (one for neg, one for pos) for each string. Could just mount a piece of DIN rail, or use an enclosure.

https://cpc.farnell.com/mersen-ferraz-s ... dp/FF04040

Thanks for this.

However you have to watch as that can’t be used as an on load isolator…

AGT wrote: ↑Sun Apr 13, 2025 8:23 pm However you have to watch as that can’t be used as an on load isolator…

Yes duely noted thanks.

The Niceic link went over alot of what i already understood, but also did not specify if a 4 pole switch splits the main rating or is for both strings equally.
I presume if they dont say it is split, it is because there is no need for a warning as such, but it is not clear given what the manufaturers of such are saying.

I will ask my electrician what he recommends.
I may have to use singles instead if i cant get an adequate answer. At least then i know for sure they will be adequate.
It makes sense to have the din rail fuses in the shed and DC isolators before each string goes underground, but id really like to be able to shut off from one place in the shed if a problem arose, rather than walk to individual arrays dotted in the garden.

You can use a 4 pole on a 2 wire system, you use links to effectively switch the 1 conductor through 2sets of poles.

So feed comes in say top of switch , broken via switch coming out of bottom of switch, link inserted feeding it into another pole at the bottom and then switched again coming out of the top.

Hi, yes thanks i understand that, whatni wanted to know is if the rating was across every contact or spilt between them.
Electrician just responded that it would apply for each contact so a 20A 4 pole switch would have 20A per pole dependant on voltage.

I was overthinking things.