shutoff switch for Panel wires before going to inverter - Junction Box/Combiner Box?

[Blue Grouse]

Hello,

Our roof top panel system will utilize 4 Arrays with 1 negative cable and 1 positive cable (8 pv cables total) so....before this wiring is routed to the Inverter, we'd like to have a shutoff switch that can handle each of the 4 arrays.

Which box would we use and....is it a Junction Box w/circuit breakers or a combiner box?

Thanks!

[Droo71]

Typically you would combine the 4 arrays with a combiner box; each array would go to a breaker (or fuse) in the combiner box; then you have a single wire at the same voltage, but combined amperage going from the combiner to your inverter.

I use a Midnite MNPV6-DISCO , so the breakers on each array are ganged together with the external disconnect handle, providing me disconnect *and* overcurrent in the single box. I see fuse-based combiners as well, where you could put a signle disconnect on the combined line external to the combiner box.

[SunEagle]

I will agree with Droo71 except to say you MUST wire the 4 arrays to a combiner box. If not then it will not be legal in the USA.

The Midnite Solar combiner provides circuit breakers which are rated for the DC voltage and I believe can be opened under load.

I have a DIY fused combiner box but feel the Midnite is a better way to go.

[Droo71]

SunEagle, I have seen arrays with voltage combinations where the array matches the MPPT controller, or the inverter -- and so the wiring is a straight home run into the controller and is never combined - so there are situations where a junction/combiner may not be the appropriate thing. NEC isn't mandating that you must combine arrays that are 'at capacity' is it? I'm not in the USA.
I *can* see that it would mandate a disconnect for each array - but I will defer to a resident to say if each disconnect would be separate, or if you'd need an enclosure to provide overcurrent and disconnect for each run.


One thing to be aware of for fused combined boxes is the VoC voltage of your array. The standard Midnite breaker is good up to 150VDC. I have 4 panels in series in my arrays -- which means my max VoC is almost 160V, not including temperature differentials.

This means I had to get the MPNV6-250DISCO , and use 300V breakers - so only 3 arrays in *that* box. Please check your array voltages and size the combiners accordingly.

If I manage to get enough off the 'to do' list, I will rewire mine to be 4 arrays of 3 panels. Yes, the amperage goes up to 36 instead of 27 , but I'm wired for 65, so lots of headroom. There's a balance between cost in breakers and cost in copper wire...

[Mike90250]

I JUST today, used the breakers on my midnight combiner box, to test the 3 strings against each other. A couple days ago, I saw ONE panel on the array, was fogged up differently ( right at sunrise ) than the others ! Arghh !! Not a section of 1 panel, but 1 perfectly even discolor panel against all the others. Today, I confirmed in about 10 minutes of flipping the breakers for each string, each 1kw string was within 15w of the others. So it's not totally dead via a quick check. About 2 weeks of rain in the forecast, so further testing will have to wait.

[Droo71]

I JUST today, used the breakers on my midnight combiner box, to test the 3 strings against each other. A couple days ago, I saw ONE panel on the array, was fogged up differently ( right at sunrise ) than the others ! Arghh !! Not a section of 1 panel, but 1 perfectly even discolor panel against all the others. Today, I confirmed in about 10 minutes of flipping the breakers for each string, each 1kw string was within 15w of the others. So it's not totally dead via a quick check. About 2 weeks of rain in the forecast, so further testing will have to wait.

They are convenient. And yes, SunEagle, they are rated to open under load. I prefer the DISCO boxes - they have a big red handle on the outside that gangs all the breakers together for 'on/off' -- but you CAN easily pop a handle out of the gang to have it off - or on - by itself.

Like i said, the only thing to watch is if you need 150V or 300V breakers for your array; they are designed for residential arrays so the expectation is generally not to get up above 300V.

dt

[SunEagle]

SunEagle, I have seen arrays with voltage combinations where the array matches the MPPT controller, or the inverter -- and so the wiring is a straight home run into the controller and is never combined - so there are situations where a junction/combiner may not be the appropriate thing. NEC isn't mandating that you must combine arrays that are 'at capacity' is it? I'm not in the USA.
I *can* see that it would mandate a disconnect for each array - but I will defer to a resident to say if each disconnect would be separate, or if you'd need an enclosure to provide overcurrent and disconnect for each run.


One thing to be aware of for fused combined boxes is the VoC voltage of your array. The standard Midnite breaker is good up to 150VDC. I have 4 panels in series in my arrays -- which means my max VoC is almost 160V, not including temperature differentials.

This means I had to get the MPNV6-250DISCO , and use 300V breakers - so only 3 arrays in *that* box. Please check your array voltages and size the combiners accordingly.

If I manage to get enough off the 'to do' list, I will rewire mine to be 4 arrays of 3 panels. Yes, the amperage goes up to 36 instead of 27 , but I'm wired for 65, so lots of headroom. There's a balance between cost in breakers and cost in copper wire...

Unless someone says where they live I have to use what I know is Electric Code in the USA. Here the NEC says that any more than two parallel strings require some type of combiner box. Now if the inverter can handle 3 inputs and you want to run 3 pairs of wires a long way you should be ok. But the OP was looking for a way to run a single pair of wires from 4 strings which requires some type of combiner box with over current protection for each "string".

[Droo71]

Unless someone says where they live I have to use what I know is Electric Code in the USA. Here the NEC says that any more than two parallel strings require some type of combiner box. Now if the inverter can handle 3 inputs and you want to run 3 pairs of wires a long way you should be ok. But the OP was looking for a way to run a single pair of wires from 4 strings which requires some type of combiner box with over current protection for each "string".

I've seen rule 690.9 (A) .. it specifies physical disconnects / load breaks..-- and a related rule now specifies rapid shut off. I've not seen a 'must be combined'. I always thought combining requirements were a function of voltage/amperage/other end device, and it was only the load break per string /physical disco/rapid shutdown that was the 'hard and often misunderstood' requirements.

Learn something new every day. Not that I'll ever be using the NEC in my installs. Its interesting some of the odd differences.

[SunEagle]

I've seen rule 690.9 (A) .. it specifies physical disconnects / load breaks..-- and a related rule now specifies rapid shut off. I've not seen a 'must be combined'. I always thought combining requirements were a function of voltage/amperage/other end device, and it was only the load break per string /physical disco/rapid shutdown that was the 'hard and often misunderstood' requirements.

Learn something new every day. Not that I'll ever be using the NEC in my installs. Its interesting some of the odd differences.

I don't currently have a copy of the NEC but I know that somewhere it states you are required to use a combiner with over current protection if you have more than 2 strings. The over current protection keeps you from backfeeding into another string should one short out and it also provides a way of disconnecting each string safely instead of opening up the connectors like the MC4 type.

The NEC is similar to the codes in Canada but your are correct other countries follow their own rules if any.

[peakbagger]

The soladeck roof boxes had space for breakers and could be used for a combiner. I think mine came with just pull out disconnects mounted on a Din Rail but there was plenty of room. I got creative and mounted a midnight solar SPD on one of the knockouts and wired to the wires heading into the house. One thing to note, it requires a screwdriver to open the cover to get to any of the internal switches or breakers. I like it as it flashing into the shingles nicely and was relatively low profile.

[Droo71]

I don't think that'll meet code for the OPs situation -- i believe you have to be able to disconnect via a handle or a switch - not 'having to open a box with tools to access the disconnect'....

[nerdralph]

IMO makes DC isolators. 4 of them may do what you want.

https://www.imopc.com/pages/sim