Hello everyone, I am a new user in photovoltaics and I have a problem with my Voltronics Axpert Max II 11kW, I have a question that I cannot solve regarding the wiring of this inverter.

On page 8 of the manual it says:

WARNING: Because this inverter is non-isolated, only three types of PV modules are acceptable: single crystalline and polycrystalline with class A-rated and CIGS modules.
To avoid any malfunction, do not connect any PV modules with possible current leakage to the inverter. For example, grounded PV modules will cause current leakage to the inverter. When using CIGS modules, please be sure NO grounding.
CAUTION: It's required to use PV junction box with surge protection. Otherwise, it will cause damage on inverter when lightning occurs on PV modules.

I have 30 meters between the panels and the inverter, I installed a DC box at the level of the panels in which there is fuse, circuit breaker, and anti-surge module (bipolar connect to the ground), and another box near the inverter with circuit breaker and surge protection module for each MPPT input.

At the beginning I did not have a box near the panels (only near the inverter), but recently I installed the DC box near the panels, and the inverter sizzles (electronic noise) more than before (even at night).

It is noted that the panels must be isolated from the ground, but the principle of a surge protector is to send the surge to the ground (and a surge protector always has a small current leakage), so this contradicts the manual ...? (what risk?)

Why does my inverter sizzle when the panels are connected? (leakage to earth? two surge protectors per mppt is that too much?)

Does anyone have a clear wiring diagram for wiring the PV part of the inverter (for Voltronics models or equivalent) to confirm my correct wiring(?Solar panels->fuse->Circuit breaker->surge protection->30m of cable->Circuit breaker->surge protection->inverter)

How to protect against overvoltages if we must not connect to the ground?

Thanks for any help/explanations.

18 hours ago, Br999 said:

Why does my inverter sizzle when the panels are connected? (leakage to earth? two surge protectors per mppt is that too much?)

With all these higher voltage SCC models, PV- has a bus voltage square wave with respect to earth. This is because the neutral output of the inverter is at earth potential, and the neutral output of the inverter connects to either BUS+ or BUS- depending on which half of the AC-out wave is being generated. Obviously during the day, PV+ has PV voltage added to that (though the polarity is opposing, so you never see BUS voltage added to PV voltage, fortunately). This is presumably the source of your sizzling noise. I note that if your panel voltage is high (say 480 V), then your bus voltage will be about the same, so you'll have a positive ~480 V square wave to earth from PV+, and a -480 V square wave on PV-.

I don't have a high voltage SCC model, so I've never thought about how lightning protection devices would work. I note that 480 V is a fair bit more than you'd see at the peak of a utility sine wave, so your protection devices might be conducting at too low a voltage. I guess you could check current in the earth lead of the protection devices; I would expect only a few mA of current.

The sizzling might also be caused by something breaking down. If you hear it at night (though then the bus voltage will be lower, so you may not), you could try to use the darkness to try and find any arcing. If the sizzling is really coming from the inverter, it may be arcing in there, or it might just be some capacitors acting like electrostatic speakers. Some capacitors seem to be more acoustically noisy than others.

in fact the sizzling sounds a bit like the noise an induction hob can make maybe that's normal...

on the other hand I still do not understand why in the manual apparently it is clearly indicated that the solar panels must not be connected to the ground, but then what happens if an overvoltage occurs? the surge will be directed to earth by the surge arresters and what will happen? Will the inverter burn ?

is there any other solution to limit surges without having to use earth??

Putting a lightning arrester just after the panels and just before the inverter seems like a good idea to you given the cable distance?

6 hours ago, Br999 said:

in the manual apparently it is clearly indicated that the solar panels must not be connected to the ground,

That's because of the square waves I mentioned. 

6 hours ago, Br999 said:

what happens if an overvoltage occurs? the surge will be directed to earth by the surge arresters and what will happen? Will the inverter burn ?

It will suffer an overload. Whether it burns or not depends on many factors. But you're most likely much better off with the surge arrestors there.

7 hours ago, Br999 said:

is there any other solution to limit surges without having to use earth??

There are protection devices (MOVs) across the AC input (line to neutral), but also similar ones from line and neutral to earth. Utility surges are generally line to neutral, while lightning surges are generally line or PV to earth.

7 hours ago, Br999 said:

Putting a lightning arrester just after the panels and just before the inverter seems like a good idea to you given the cable distance?

If you mean two sets of arrestors, one on the roof and one near the inverter(s), that sounds uncommon to me, but I'm no lightning expert.

thank you for answering me and for all this information