Driving me crazy!!! PV breakers are "polarizing"

[will_fish]

Good afternoon, I was about ready to purchase my panels and associated breakers but can’t quite figure out the PV breaker situation. I’ve read several “heated” debates (literally) and now I’m not really sure what’s considered safe and/or effective. Several experts seem to indicate that polarized PV breakers should NOT be used and their logic seems reasonable to me. @Hedges

Initially, I was planning to use Midnite Solar products (MNPV6 + MNEPV20 [4] + MNSPD-300-DC). Then I made the mistake and decided to do a little more research and went down a path that does not seem to end. Before I knew it, I was reading posts back from 2010 (from Robin @ MidNite Solar).

I was planning to use 8 Rec Alpha 365W panels with 4 series. Here are the key questions I can’t figure out:

• Is there an ideal (and potentially NEC compliant) solution for non-polarized PV breakers? Or would fuses be the best option?
  (I read somewhere that Midnite Solar was coming out with a new non-polarized version this year but I don’t see any options on their site)
• Is there an NEC requirement to breaker/fuse the negative PV wire for transformer-less inverters (e.g., Growatt SPF 3000)?
  (this pdf currently posted at MidNite solar for the MNPV12 seems to indicate that it’s required for transformer-less systems – see top of Page 7)
• What is suggested for odd breaker specs?
  (e.g., Rec Alpha states a max fuse rating of 25A but I don’t see 25A PV breakers or fuses from MidNite Solar. Based on ISC for the panel which is 10.52, I would have assumed that a 20A would be recommended)

Any suggestions or guidance would be greatly appreciated. Hoping to end analysis paralysis with some help ?

 

[Kcdaniels]

Good afternoon, I was about ready to purchase my panels and associated breakers but can’t quite figure out the PV breaker situation. I’ve read several “heated” debates (literally) and now I’m not really sure what’s considered safe and/or effective. Several experts seem to indicate that polarized PV breakers should NOT be used and their logic seems reasonable to me. @Hedges

Initially, I was planning to use Midnite Solar products (MNPV6 + MNEPV20 [4] + MNSPD-300-DC). Then I made the mistake and decided to do a little more research and went down a path that does not seem to end. Before I knew it, I was reading posts back from 2010 (from Robin @ MidNite Solar).

I was planning to use 8 Rec Alpha 365W panels with 4 series. Here are the key questions I can’t figure out:

• Is there an ideal (and potentially NEC compliant) solution for non-polarized PV breakers? Or would fuses be the best option?
  (I read somewhere that Midnite Solar was coming out with a new non-polarized version this year but I don’t see any options on their site)
• Is there an NEC requirement to breaker/fuse the negative PV wire for transformer-less inverters (e.g., Growatt SPF 3000)?
  (this pdf currently posted at MidNite solar for the MNPV12 seems to indicate that it’s required for transformer-less systems – see top of Page 7)
• What is suggested for odd breaker specs?
  (e.g., Rec Alpha states a max fuse rating of 25A but I don’t see 25A PV breakers or fuses from MidNite Solar. Based on ISC for the panel which is 10.52, I would have assumed that a 20A would be recommended)

Any suggestions or guidance would be greatly appreciated. Hoping to end analysis paralysis with some help ?

I'm sorry I can't be much help but I do understand how you feel ?
I've researched for months now and feel like I'm drowning in information overload !!!! A lot of conflicting information out there and for a newbie like me it could be dangerous ?

 

[Bud Martin]

Good afternoon, I was about ready to purchase my panels and associated breakers but can’t quite figure out the PV breaker situation. I’ve read several “heated” debates (literally) and now I’m not really sure what’s considered safe and/or effective. Several experts seem to indicate that polarized PV breakers should NOT be used and their logic seems reasonable to me. @Hedges

Initially, I was planning to use Midnite Solar products (MNPV6 + MNEPV20 [4] + MNSPD-300-DC). Then I made the mistake and decided to do a little more research and went down a path that does not seem to end. Before I knew it, I was reading posts back from 2010 (from Robin @ MidNite Solar).

I was planning to use 8 Rec Alpha 365W panels with 4 series. Here are the key questions I can’t figure out:

• Is there an ideal (and potentially NEC compliant) solution for non-polarized PV breakers? Or would fuses be the best option?
  (I read somewhere that Midnite Solar was coming out with a new non-polarized version this year but I don’t see any options on their site)
• Is there an NEC requirement to breaker/fuse the negative PV wire for transformer-less inverters (e.g., Growatt SPF 3000)?
  (this pdf currently posted at MidNite solar for the MNPV12 seems to indicate that it’s required for transformer-less systems – see top of Page 7)
• What is suggested for odd breaker specs?
  (e.g., Rec Alpha states a max fuse rating of 25A but I don’t see 25A PV breakers or fuses from MidNite Solar. Based on ISC for the panel which is 10.52, I would have assumed that a 20A would be recommended)

Any suggestions or guidance would be greatly appreciated. Hoping to end analysis paralysis with some help ?

So you will have 8 PV panels and you are going to wire them up as 4s2p, correct? So if you read that 'heated debate about the polarized circuit breakers, post #6 is how you do it by using fuse for each string of the PV panels and then you feed that to the polarized breaker as Hedges had explained.

DC breaker wiring

The topic of DC breaker wiring polarity (ie, which side of the breaker is the source and which is the sink) has been raised a few times on the forum. I'm not sure if this clip has been posted before, but if not this is a must for everyone to watch.

diysolarforum.com

 

[rhino]

It does say MAX rating so there is nothing wrong with using 20A breaker with that panel.

 

[will_fish]

So you will have 8 PV panels and you are going to wire them up as 4s2p, correct? So if you read that 'heated debate about the polarized circuit breakers, post #6 is how you do it by using fuse for each string of the PV panels and then you feed that to the polarized breaker as Hedges had explained.

DC breaker wiring

The topic of DC breaker wiring polarity (ie, which side of the breaker is the source and which is the sink) has been raised a few times on the forum. I'm not sure if this clip has been posted before, but if not this is a must for everyone to watch.

diysolarforum.com

Thanks for the info. Yes, the panels will be wired as 4s2p. So I could put 4 fuses (max allowed) in an MNPV6 and then add another MNPV6 with a polarized breaker (~70A breaker). I wonder if I could use a non-polarized breaker (MNEDC70) for the disconnect which would save me an additional box (already have a quad box with battery breaker). I'm not clear on the value of the polarized disconnect breaker if there are also 4 fuses (one for each string).

 

[rhino]

I'm not quite sure why you are wanting to use a polarized breaker? All of my arrays are 5 or 4 in series and 2 in parallel using 2 Midnite non-polarized breakers for each string (so 2 breakers per array in an MNPV6) along with a Midnite lightning protector. My caveat being they are on a top of pole mount which does not have as strict of requirements if they were on a house roof.

 

[will_fish]

I'm not quite sure why you are wanting to use a polarized breaker? All of my arrays are 5 or 4 in series and 2 in parallel using 2 Midnite non-polarized breakers for each string (so 2 breakers per array in an MNPV6) along with a Midnite lightning protector. My caveat being they are on a top of pole mount which does not have as strict of requirements if they were on a house roof.

I may be missing something important here. Does Midnite Solar make a non-polarized din breaker (that fits in the MNPV6)? I'm only finding the MNEPV din breakers on their site which are all polarized. Also, my panels will be ground mount or on a detached shed so no panels on the house roof. Thanks for the help

 

[rhino]

Are you looking at their breaker poster? http://www.midnitesolar.com/pdfs/breakers_11x17.jpg (and I actually have the MNPV6-250)

Edit: I'm using MNEPV15-300

 

[rhino]

I think I see your problem... If you do have the MNPV6 and not the MNPV6-250 you are limited to 150V breakers non-polarized instead of the 300V non-polarized breakers available with the MNPV6-250. Four of the REC 365W panels in series would put you well over 150V Voc and the MNPV6 only has option for polarized 300V breakers. The polarized ones are less than half the price and half the width of the non-polarized ones so that must be why there is case for polarized ones.

 

[will_fish]

I think I see your problem... If you do have the MNPV6 and not the MNPV6-250 you are limited to 150V breakers non-polarized instead of the 300V non-polarized breakers available with the MNPV6-250. Four of the REC 365W panels in series would put you well over 150V Voc and the MNPV6 only has option for polarized 300V breakers. The polarized ones are less than half the price and half the width of the non-polarized ones so that must be why there is case for polarized ones.

Apologies for the confusion....the plan is for 2s4p (I misstated when I responded to @Bud Martin). My inverter (Growatt SPF3000LTM) only supports 145V open circuit so I cannot have 4s2p with the Rec Alpha panels (since it would be 176V). Regarding the Midnite breakers, the breaker poster does not match their web site for available breakers and I cannot find anywhere to buy the non-polarized 150V din breakers that are listed as "NEW".

 

[Colorado_Al]

Why wouldn't you use something like this:

4 String PV Combiner Box with Lightning Arrester & 10A Rated Current Fuse & Circuit Breakers for On/Off Grid Solar System | ECO-WORTHY

ECO-WORTHY 4 String PV Combiner Box is suitable for photovoltaic grid-connected and off-grid power generation systems. Its main function is to converge the input of PV array. It can support solar panel system up to 700W in 12V system, 1400W in 24V system, 2800W in 48V system. Easy installation...

www.eco-worthy.com

Or does that not have enough capacity?

 

[chrisski]

Why wouldn't you use something like this:

4 String PV Combiner Box with Lightning Arrester & 10A Rated Current Fuse & Circuit Breakers for On/Off Grid Solar System | ECO-WORTHY

ECO-WORTHY 4 String PV Combiner Box is suitable for photovoltaic grid-connected and off-grid power generation systems. Its main function is to converge the input of PV array. It can support solar panel system up to 700W in 12V system, 1400W in 24V system, 2800W in 48V system. Easy installation...

www.eco-worthy.com

Or does that not have enough capacity?

Not a fan of the Ecoworthy Combiner Box.

I tried to order it, but poor customer service and bait and switch made me cancel my order. Other reasons I don’t like it is to make it appeal to the new DIY crowd, they add MC4 for quick disconnection When adding a string of panels. It’s not that hard to feed a wire through a cable gland and screw it into a circuit breaker. Looks like they have you do that to the combined power anyway. If you buy theif kit, then you will need 10 amp C/B for their panels, but if you have 15 watt panels, 10 amps is not enough, you’d need 15 amps. If you have 2 strings coming in, you’ve just paid for two more strings you’ll probably never use.

 

[Colorado_Al]

Not a fan of the Ecoworthy Combiner Box.

I tried to order it, but poor customer service and bait and switch made me cancel my order. Other reasons I don’t like it is to make it appeal to the new DIY crowd, they add MC4 for quick disconnection When adding a string of panels. It’s not that hard to feed a wire through a cable gland and screw it into a circuit breaker. Looks like they have you do that to the combined power anyway. If you buy theif kit, then you will need 10 amp C/B for their panels, but if you have 15 watt panels, 10 amps is not enough, you’d need 15 amps. If you have 2 strings coming in, you’ve just paid for two more strings you’ll probably never use.

The OP has 4 strings.

 

[will_fish]

Why wouldn't you use something like this:

4 String PV Combiner Box with Lightning Arrester & 10A Rated Current Fuse & Circuit Breakers for On/Off Grid Solar System | ECO-WORTHY

ECO-WORTHY 4 String PV Combiner Box is suitable for photovoltaic grid-connected and off-grid power generation systems. Its main function is to converge the input of PV array. It can support solar panel system up to 700W in 12V system, 1400W in 24V system, 2800W in 48V system. Easy installation...

www.eco-worthy.com

Or does that not have enough capacity?

Thanks for the suggestion. I had looked at that box but need 20A (per fuse/breaker minimum) and ideally 25A (per Rec Alpha specs). The ISC for the panels is 10.52 so multiplying that by 1.56 would be 16.42 so rounding up means minimum 20A per fuse/breaker. Also, I'm not sure any of the parts in that box are "listed". I'm all for saving money but I'm trying to get this "right" from a safety perspective. If I burn down the shed, my wife is likely to shut down my solar project

I'm good with spending a few extra bucks in this area but the "right" parts just seem difficult to find. It seems Midnite Solar has acknowledged the need for a non-polarized PV breaker (and even built one) but unfortunately they are not being sold anywhere. At this point, I'm considering going down to 2 strings and buying another inverter that will support more voltage (up to 250V). Fewer issues with 2 strings and I'll sleep better

 

[rhino]

This one should work: https://www.solar-electric.com/midnite-solar-mnepv-20-amps-circuit-breaker.html even though it is polarized the MNPV6 manual clearly shows how to install it (facing up like a normal breaker would look).

 

[will_fish]

Good afternoon, I woke up this morning and had an idea for my solar panel breakers/fuses which hopefully fills the gap from the polarized PV breakers. Here's what I'm thinking:

1) Place 25A inline fuses on each series (25A aligns with panel spec)
2) Use Midnite Solar 20A PV breakers (MNEPV20) for each series in a combiner box with Midnite Solar SPD (which would be located out by panels). The 20A breakers should somewhat prevent the 25A inline fuses from blowing. So hopefully the inline fuses are just precautionary and won't have to be replaced very often (if at all)
3) Add 2 70A breakers (MNEDC70) near the inverter (on positive and negative lines and probably gang together). I came up with 70A by multiplying ISC X # of series X 1.56 (10.52 ISC X 4 series X 1.56 = ~66A and round up to 70A breaker)

The goal was to fill the gap from the polarized PV breakers and hopefully the inline fuses accomplish that goal. Also, I still want the PV breakers per string for maintenance/testing/troubleshooting. Our initial set of panels will be facing 3 directions and I want to understand panel production per direction so we can plan the best direction for future panels.

I've attached a draft design. Feedback welcome....

 

[chrisski]

If I’m reading this correcty you have a 25 amp fuse and a 20 amp circuit breaker on the same line. I’d just go with one or the other.

You have a 48 volt system and I have only built 12, so the rest may not apply. Post combiner, if you’re pllanning on having 50 to 70 amps through AWG 6 wire, first be sure the ampacity is there (Doesn‘e exceed the Mac amps for the wire at a given temp). My gut tells me that 6 AWG is good only for very short runs, and solar combiners are unlikely to be that close to the main battery pack.

As a gauge, my trailer battery can push 50 amps. The original single battery for my solar upgrade was 6 AWG, but was 2’ long. I moved that to between six and 8 feet away, and upped the gauge to 2 AWG.

On an unrelated note, you may getmore people to review the diagram by positng a pic in the body instead of a PDF.

 

[will_fish]

Good afternoon, I woke up this morning and had an idea for my solar panel breakers/fuses which hopefully fills the gap from the polarized PV breakers. Here's what I'm thinking:

1) Place 25A inline fuses on each series (25A aligns with panel spec)
2) Use Midnite Solar 20A PV breakers (MNEPV20) for each series in a combiner box with Midnite Solar SPD (which would be located out by panels). The 20A breakers should somewhat prevent the 25A inline fuses from blowing. So hopefully the inline fuses are just precautionary and won't have to be replaced very often (if at all)
3) Add 2 70A breakers (MNEDC70) near the inverter (on positive and negative lines and probably gang together). I came up with 70A by multiplying ISC X # of series X 1.56 (10.52 ISC X 4 series X 1.56 = ~66A and round up to 70A breaker)

The goal was to fill the gap from the polarized PV breakers and hopefully the inline fuses accomplish that goal. Also, I still want the PV breakers per string for maintenance/testing/troubleshooting. Our initial set of panels will be facing 3 directions and I want to understand panel production per direction so we can plan the best direction for future panels.

I've attached a draft design. Feedback welcome....

Here's the current plan that I mentioned above...

 

[will_fish]

If I’m reading this correcty you have a 25 amp fuse and a 20 amp circuit breaker on the same line. I’d just go with one or the other.

You have a 48 volt system and I have only built 12, so the rest may not apply. Post combiner, if you’re pllanning on having 50 to 70 amps through AWG 6 wire, first be sure the ampacity is there (Doesn‘e exceed the Mac amps for the wire at a given temp). My gut tells me that 6 AWG is good only for very short runs, and solar combiners are unlikely to be that close to the main battery pack.

As a gauge, my trailer battery can push 50 amps. The original single battery for my solar upgrade was 6 AWG, but was 2’ long. I moved that to between six and 8 feet away, and upped the gauge to 2 AWG.

On an unrelated note, you may getmore people to review the diagram by positng a pic in the body instead of a PDF.

Thanks for the reminder on the wire distance. I just ran the numbers through this calculator with 2% loss and said 6 AWG would suffice. For 1% loss then I would need to use 4 AWG.

 

[jameshowison]

Thanks for the suggestion. I had looked at that box but need 20A (per fuse/breaker minimum) and ideally 25A (per Rec Alpha specs). The ISC for the panels is 10.52 so multiplying that by 1.56 would be 16.42 so rounding up means minimum 20A per fuse/breaker. Also, I'm not sure any of the parts in that box are "listed". I'm all for saving money but I'm trying to get this "right" from a safety perspective. If I burn down the shed, my wife is likely to shut down my solar project

I'm good with spending a few extra bucks in this area but the "right" parts just seem difficult to find. It seems Midnite Solar has acknowledged the need for a non-polarized PV breaker (and even built one) but unfortunately they are not being sold anywhere. At this point, I'm considering going down to 2 strings and buying another inverter that will support more voltage (up to 250V). Fewer issues with 2 strings and I'll sleep better

For anyone else coming this way and confused about the Midnite 150v non-polarized breakers. As of October 2022, They are shown in a jpg on the front page of the website, but not in their product list. So I called and they said,”oh, those were going to be made when we made that brochure about 2 years ago, but they didn’t get made”. I asked why they didn’t take them off the brochure and, well, the conversation wasn’t useful past that point. A bit bizarre.