Surge Protection for Victron solar products?

Been down this rabbit hole with my cabin setup and honestly the Victron documentation is like reading ancient Sanskrit — technically complete, utterly baffling.

The OVC II rating on the PV input of something like the Multi RS essentially means it's designed to handle the transient surges you'd expect from normal solar array wiring indoors, but not the kind of brutal spike that comes from a direct or nearby lightning strike. That's OVC III / IV territory and requires external protection upstream.

So practically speaking — do you need a dedicated surge protection device (SPD) on the DC side before your Victron kit? Almost certainly yes if your array is on a roof with any meaningful cable run. I've got a Renogy SPD slapped in before my charge controller on the cabin, which probably cost me less than a decent pub lunch and gives me considerably more peace of mind than the pub lunch ever did.

On the AC output side it's worth thinking about separately — especially if you're running a Multi as a proper ESS and feeding sensitive loads.

Couple of questions worth throwing out to the group:

• Anyone using dedicated Type 1+2 combined SPDs on their motorhome installs, or is that overkill for a vehicle?
• Does the relatively short cable run on a van roof actually reduce your risk enough to skip it?

Feels like this is one of those areas where half the community wings it and gets lucky, and the other half discovers why insurance companies ask awkward questions. Would love to hear what people are actually doing in practice rather than what the manuals suggest you do.

@Mel1980 Ha, know that feeling — spent ages staring at the Victron MPPT docs for my boat setup trying to work out the same thing.

Quick question though: are you running string fusing or relying solely on the combiner box for your OVC protection? I ended up going down a rabbit hole about whether the built-in reverse current protection on the SmartSolar actually covers what you'd need for a proper OVC II compliance scenario.

Also — is this for a static cabin install or does the moveable/transportable classification change the requirements for you? I've seen conflicting info about whether EN 62109 applies differently depending on that.

Has anyone here actually had a Victron install signed off by a DNO or MCS assessor and asked them directly? Feels like that's the only way to get a definitive answer rather than piecing together forum posts and half-translated manuals.

@Mel1980 Victron docs are written by engineers for engineers who apparently communicate telepathically.

On the OVC II rating — that's your overvoltage category, basically telling you how much transient spike the input can handle before it becomes a very expensive paperweight. For PV inputs on the SmartSolar MPPTs it's relevant because

@Mel1980 Welcome to the forum — great first technical post, you'll fit right in here!

To pick up where the others left off on OVC II: in practical terms for a UK installation, the PV input overvoltage category rating tells you what kind of surge the device can survive internally, but it doesn't mean you're protected against transient spikes arriving from the array itself. Those can absolutely exceed the rating during a nearby lightning strike or even just a long cable run acting as an antenna.

For my static caravan setup I added dedicated DC surge protection arresters between the array combiner and the MPPT — specifically rated SPDs with appropriate Uc voltage above your Voc. Victron themselves recommend this in their wiring unlimited guide (page worth finding).

The OVC rating and SPD protection are two separate layers — both matter.

@Mel1980 the OVC II rating basically means your Victron MPPT expects Type 2 surge protection on the PV strings — so you want a proper DC SPD wired in before the charge controller, not just crossed fingers and a fuse. Citel or Dehn are the go-to brands, sized to your array's Voc. Worth checking your actual open-circuit voltage at the lowest expected temperature too, because British "summer" has a nasty habit of producing surprisingly cold clear mornings that spike your Voc higher than the datasheet suggests — ask me how I know. 😬