Pv combiner box

allinthehead

I'm getting another 15 panels fitted on my roof in a couple of months and I was thinking about string overcurrent protection and dc surge protection.

I never hear anyone talking about it.

Was thinking of installing something like this -

https://www.etek-china.com/combiner-box/ekdb-pv-2-2-m

Any thoughts?

Big Lar

Perhaps your not but if your putting 15 panels on a single string then you would deffo be in the overvoltage and possibly overcurrent category.

Have a look at your inverter stats and see what's the max voltage per string, then check the panels, depends on your inverter but bout 12 seems to be the max from my knowledge.

jasgrif11

In general is it advised to add surge protection to a solar install? I don’t have it on mine

allinthehead

https://www.boards.ie/discussion/comment/121501982#Comment_121501982

No, that won't be an issue for me.

allinthehead

https://www.boards.ie/discussion/comment/121502093#Comment_121502093

Ac and dc surge protection is a regulation in is10101 but I rarely see it installed or hear any talk of it especially dc.

bullit_dodger

Good point - where would you get a DC surge? I guess the sun coming out from behind a cloud might be a cause. But thats something that is a regular day-to-day action that the inverter doesn't even think about and should handle it as it's inherently designed to?

allinthehead

https://www.boards.ie/discussion/comment/121502717#Comment_121502717

Lightning.

bullit_dodger

https://www.boards.ie/discussion/comment/121502886#Comment_121502886

Ha - forgot about that. You think a DC surge protector could handle a lighting strike? I'd have my doubts :-)

allinthehead

https://www.boards.ie/discussion/comment/121502911#Comment_121502911

Not much survives a direct strike, would help with indirect.

2011

https://www.boards.ie/discussion/comment/121502218#Comment_121502218

I had a look at this. It would seem to me that IS10101 states that surge protection on the DC side may be required. See the last line in the table below.

allinthehead

https://www.boards.ie/discussion/comment/121508776#Comment_121508776

That would seem to suggest that it's practically never required as you wouldn't see a residential installation where the panels are that far from the inverter.

2011

https://www.boards.ie/discussion/comment/121509085#Comment_121509085

That is the way I am reading it too.

However, given the choice I would install them on both sides of the inverter.

10-10-20

https://www.boards.ie/discussion/comment/121508776#Comment_121508776

What's "Ng" in the table referring to?

allinthehead

https://www.boards.ie/discussion/comment/121509158#Comment_121509158

Lightning ground flash density.

allinthehead

https://www.boards.ie/discussion/comment/121509095#Comment_121509095

Ya, I'm still installing it anyway along with the overcurrent/short circuit protection.

graememk

It for sure won't do any harm. And if it's a personal project, the cost of surge protection is trivial.

10-10-20

https://www.boards.ie/discussion/comment/121509188#Comment_121509188

Ok, so how do you work that out? Is that a constant?

allinthehead

https://www.boards.ie/discussion/comment/121509201#Comment_121509201

Agreed.

https://www.boards.ie/discussion/comment/121509239#Comment_121509239

Ya I think it's a constant here. Number of ground strikes per km2 per year.

For Ac surge protection there's a similar formula or a risk assessment. Basically if the cost of putting in surge protection is less than the cost of the equipment installed in the installation then surge protection is required. Risk assessment goes like this, is there a tv/computer/fridge? If yes then surge protection required.

2011

https://www.boards.ie/discussion/comment/121509239#Comment_121509239

"lighting ground flash density", which is lighting strikes per km squared per year. I assume that this can be looked up somewhere, not sure where to be honest. Perhaps Met Eireann can advise.

I found this though:

https://nhess.copernicus.org/articles/14/815/2014/nhess-14-815-2014.pdf

10-10-20

https://www.boards.ie/discussion/comment/121509280#Comment_121509280

https://www.boards.ie/discussion/comment/121509304#Comment_121509304

Funny that. I had a lightening strike around 15m from the house this year and it was the Virgin Media signal cable which brought the surge in to the house. Zero effect on the electrical/solar side of things, but wiped out my ethernet by propagating into my CAT5 off the Virgin Media box. Anyway.

So going off that PDF parts of Ireland appear to be Np of 0.1.

So L = 115 / 0.1 = 1150

So only if you were doing a 1.15km run of cable would you install an SPD.

But in places like Eastern France the Np would be 3.0, so:

L = 115 / 3 = 38.3

So a run of greater than 39m of cabling would be recommended to have surge protection on it. Makes sense.

graememk

https://www.boards.ie/discussion/comment/121509392#Comment_121509392

1.15km run LOL! you could be in the next townland .. what would the cable losses on that be?

2011

https://www.boards.ie/discussion/comment/121509411#Comment_121509411

That depends, the losses (in Watts) are the square of the current times the resistance of the cable.