Breakers/ Fuses on positive and negative pv wires

ligwyd

Using Solark 15K transformer-less Inverter.

3 strings of 8 panels with each string going to its own mppt.

Do both positive and negative pv wires need to be fused?

BB.

Do you have a link to a manual for your system? (I am not having much luck a manual for that unit?)...

In general, for "floating" power systems (transformerless GT-Inverters are generally "floating")--There should be over current protective devices (OCPD) on each lead (+ and - in the case of solar).

In the US, typically, Double pole breakers so that if one 1/2 the circuit pops a breaker, then the second breaker is also tripped--This helps ensure that neither the + or - leads are energized (I.e., a tripped breaker--Service person touches the "untripped" power lead--Could get a shock/electrocuted.

Using standard fuses--are less than ideal as that one fuse blowing does not "turn off" the other leg from the solar array.

Some examples of 2 pole breakers (scroll down a bit):

https://www.solar-electric.com/catalogsearch/result/?q=Breaker+30amp.+2+polos+120v

With the newer requirements for roof top remote disconnects--Here is an example that includes fuses per +/- line (option), and disconnects all +/- lines for emergency power off:

https://www.solar-electric.com/midnite-solar-mnpv16hv-dltl-4x.html
https://www.solar-electric.com/lib/wind-sun/MNRapidShutdown.pdf

I am really not that familiar with the new industry requirements, the NEC requirements (different athorities can use different "dated" codes, etc.)--And the new hardware out there for supporting these newer requirements.

Our host, NAZ, has engineers that are trained in requirements and know their product lines... As always, start with the installation manual for your hardware--And work with a knowledgeable supplier/installer--Especially if this is your first install. (I do not work for NAZ--Just a volunteer moderator here).

https://solar-electric.com/

The old requirement of just protecting the "Hot Lead(s)" is based on the return lead(s) being grounded to safety ground (I.e., the North American 120/240 VAC split phase power--Has the White/Neutral lead connected to the Green Wire safety ground--Typically in the main breaker panel). When you have Neutrals "ground bonded", the neutral lead cannot go above "zero volts" and therefore does not need a fuse/breaker/switch or 2 pole breaker/switch). (shorting a neutral to ground--Zero volts to zero volts, no "excessive" current flow / over voltage to protect against).

-Bill

ligwyd

Hi there Bill. Here is a link to the product. I will look into the manual also.

Always appreciate your feed back.

https://www.sol-ark.com/sol-ark-15k-all-in-one/

BB.

Looking at the manual:



Because the Solar input has 3 independent MPPT inputs... The "solar panels" each have a dedicated 2 wire MPPT input (3x total). And the wiring specification limits the solar array to 1 or 2x parallel strings per MPPT input...

So, from those specifications, there are no requirements for fuses or circuit breakers (not needed) for the solar array inputs as long as you meet these instructions.

Because you have no parallel connections, there are no fusing/breaker requirements to limit "excessive current" from short circuits (such as 3x or more parallel circuits--One string gets shorted and the other N-1 parallel strings feeding short circuit current into the one bad string).

The only requirement that you may still have--That is a roof top/solar array emergency disconnect. Or if your building inspector (AHJ--Athority having juristriction) required the extra equipment.

-Bill "from what I can see" B.

ligwyd

30A Isc or 44A Isc? The attached file shows to be 30A Isc max or damage occurs. Where in the manual was that taken from? The section posted above stating 44A Isc? Interesting.......

ligwyd

I called Solark and they said the 44A Isc must have been from an original (older) manual and that 30A Isc is the highest it can handle without doing damage. Self limiting to 26A per mppt. They must have changed mppt circuitry over the years this Inverter has been produced......

BB.

Always go with the latest and greatest manual... The 30 vs 44 Amps Isc ratings--Ideally, MPPT should limit to its maximum rating (26 amps?) and that there is higher current available should not matter.

But, I guess it is possible that their MPPT input design is "different".

Obviously, from a safety point of view--There needs to be some max input current limit (so that internal wiring/components don't catch fire with a short circuit failure)--That may be their change in specifications/reasoning.

-Bill