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Old 01-02-2022, 12:26 PM   #1
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Parallel Solar Panel Fuses

Technically a number of solar panels in parallel should have individual fuses at the panel. Code specifies this to be the case when you exceed the individual panel maximum short circuit current which is not always specified. Practically speaking it does make sense that a short in one panel could cause all current from other panels to flow through the wire of that panel and cause a fire. So back of the envelope 4/5 x 100 watt panels could push 30 amps through 10 gauge (or less) wire which might cause a fire. AM Solar says nothing about this and I am thinking they probably don't ever add panel fuses. Anyone here with say 4 or more 100 watt panels have fuses on each individual panel? I am converting from a 2x2 series/parallel array (100 watt panels) with factory pre-wire to a 5 panel parallel array with my own 6 gauge drop and trying to decide it it would be smart to add panel fuses. All opinions and thought experiments on this are welcome!
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Old 01-02-2022, 01:18 PM   #2
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Technically a number of solar panels in parallel should have individual fuses at the panel. Code specifies this to be the case when you exceed the individual panel maximum short circuit current which is not always specified. Practically speaking it does make sense that a short in one panel could cause all current from other panels to flow through the wire of that panel and cause a fire. So back of the envelope 4/5 x 100 watt panels could push 30 amps through 10 gauge (or less) wire which might cause a fire. AM Solar says nothing about this and I am thinking they probably don't ever add panel fuses. Anyone here with say 4 or more 100 watt panels have fuses on each individual panel? I am converting from a 2x2 series/parallel array (100 watt panels) with factory pre-wire to a 5 panel parallel array with my own 6 gauge drop and trying to decide it it would be smart to add panel fuses. All opinions and thought experiments on this are welcome!
I think for your shorting scenario to be a potential problem would be if the short were in one of the wires leading to a panel. My Renogy panels have diodes in their junction boxes which prevents backflow of current into a panel which is internally shorted. Do all panels have diodes?
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Old 01-02-2022, 02:47 PM   #3
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Yes, all panel have these diodes. They are actually bypass diodes which are in parallel with each series string in the panel. They are there to prevent shaded cells from blocking all current flow and/or potentially burning out. You are probably thinking of blocking diodes which would be in series with a string and don't come standard with panels in general. That said, let's run with the bypass diode(s) shorting. In that case all other panels would send current through the shorted panel.
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Old 01-02-2022, 03:27 PM   #4
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Yes, all panel have these diodes. They are actually bypass diodes which are in parallel with each series string in the panel. They are there to prevent shaded cells from blocking all current flow and/or potentially burning out. You are probably thinking of blocking diodes which would be in series with a string and don't come standard with panels in general. That said, let's run with the bypass diode(s) shorting. In that case all other panels would send current through the shorted panel.
I think some do come with blocking diodes as well

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Old 01-02-2022, 03:40 PM   #5
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Yes, all panel have these diodes. They are actually bypass diodes which are in parallel with each series string in the panel. They are there to prevent shaded cells from blocking all current flow and/or potentially burning out. You are probably thinking of blocking diodes which would be in series with a string and don't come standard with panels in general. That said, let's run with the bypass diode(s) shorting. In that case all other panels would send current through the shorted panel.
Well then it depends on total wattage and wire gauge. I have only 200 watts of panels. 14 amp panel output total, at solar noon in summer. I have 10 gauge from each panel, good for 30 amps. I have 6 gauge from the combiner to controller, good to 50 amps. No fuse needed.
By the numbers, I wouldn't need to be fused with 400watts, but that's too close for me. I would fuse at 400 watts with my wiring.

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Old 01-02-2022, 04:13 PM   #6
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Yes, you are fine. I am exactly at that cusp you describe. 6 gauge down from combiner with a breaker down below, 10 gauge to panels which is good for 30 amps up top. At 5 x 100 watt panels you could push over that 30 amps, theoretically. My electrical sense tell me to add fuses to the panels even though it sounds like a pain and is arguably only needed for a severe corner case. I wonder how many people with 400+ watts in parallel have done this considering one of the go-to places (AM Solar) has no mention or method of integrating panel fuses with their cabling methods. Would love to hear from some of the installers on this forum.
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Old 01-02-2022, 04:35 PM   #7
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Yes, you are fine. I am exactly at that cusp you describe. 6 gauge down from combiner with a breaker down below, 10 gauge to panels which is good for 30 amps up top. At 5 x 100 watt panels you could push over that 30 amps, theoretically. My electrical sense tell me to add fuses to the panels even though it sounds like a pain and is arguably only needed for a severe corner case. I wonder how many people with 400+ watts in parallel have done this considering one of the go-to places (AM Solar) has no mention or method of integrating panel fuses with their cabling methods. Would love to hear from some of the installers on this forum.
It seems to me this theory has changed or evolved over time. About 6 or 7 years ago, Lewster took the position it wasn't necessary....but I don't recall the particulars. He may have been discussing the presence of blocking diodes.

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Old 01-03-2022, 12:00 PM   #8
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I donít have individual fuses on my five panels, just a break on the whole array at the end of the 6ga drop. I doubt in practice all of the panels at high noon could produce enough current to melt the 10ga wire insulation in the event of a short but maybe thatís my internal optimist talking. I am certain those roof-top fuses would be source of failure that would be hard to detect. Either they would corrode or blow prematurely from heat and cause a panel to go offline. From the ground youíd have no way of knowing.
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Old 01-03-2022, 01:21 PM   #9
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I donít have individual fuses on my five panels, just a break on the whole array at the end of the 6ga drop. I doubt in practice all of the panels at high noon could produce enough current to melt the 10ga wire insulation in the event of a short but maybe thatís my internal optimist talking. I am certain those roof-top fuses would be source of failure that would be hard to detect. Either they would corrode or blow prematurely from heat and cause a panel to go offline. From the ground youíd have no way of knowing.
Thanks for the feedback. I am in total agreement, not likely 5 panels could cause 10 gauge wire to flame. This reminds me a bit of UL/CSA testing where you are trying to prevent fire from every worst case corner. Reality is 5 x 100 watt panels will never produce 30 amps. 8 panels, maybe you have a concern.

I am talking to the AM Solar EE later this week. They are exclusively using Zamp panels now. I talked to Zamp about this today. They used to advocate no fuse at panel but a fuse or thermal breaker in the roof combiner box. They have switched and now are installing fuses in all their panels inside the junction box and recommend only a breaker down below before the charge controller. I believe the thermal breaker in their old junction box has problems (pretty sure mine does).

I have been watching and admiring all your fine work and tinkering in various posts. Where did you finally decide to drop down from the combiner box to your charge controller? I am thinking you ended up with is coming down the bedroom closet. If so, did you have any problem fitting the combiner box under the front road side panel?
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Old 01-04-2022, 12:03 AM   #10
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I have been watching and admiring all your fine work and tinkering in various posts. Where did you finally decide to drop down from the combiner box to your charge controller? I am thinking you ended up with is coming down the bedroom closet. If so, did you have any problem fitting the combiner box under the front road side panel?
Mine is a FC25FBT and in that model the bathroom has two 45 degree panels on either side of the door. AS uses the ne near the toilet for the black tank vent pipe. I ran my 6ga wire down from the combiner box straight down inside that chase next to the vent pipe and from there through the wall and under the twin bed to the solar charge controller with all the other electronics. I mounted the BMV712 so itís visible in the hall and penetrating into the other chase

I used AMSolarís combiner. You can see it circled in red in this photo. I used AMSolarís over priced panel mounts which allow you to adjust the height to miss it.
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Old 01-04-2022, 06:13 AM   #11
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Mine is a FC25FBT and in that model the bathroom has two 45 degree panels on either side of the door. AS uses the ne near the toilet for the black tank vent pipe. I ran my 6ga wire down from the combiner box straight down inside that chase next to the vent pipe and from there through the wall and under the twin bed to the solar charge controller with all the other electronics. I mounted the BMV712 so itís visible in the hall and penetrating into the other chase

I used AMSolarís combiner. You can see it circled in red in this photo. I used AMSolarís over priced panel mounts which allow you to adjust the height to miss it.
I have removed the panel you are talking about and was considering coming down into that chase but have not got a good bead on locating it from the roof yet. That black vent pipe must not go straight up so I am afraid I may drill into it not knowing its path yet. I am planning to mount my TX-50 display on the hall side of that chase so it would be nice to route the solar wire with it to the electronics under the bed. Did you use the overpriced AM Solar duplex cable? I used it 4 years ago when I did my series/parallel panel to Airstream prewire junction box install. Honestly it did not hold up to sun/UV exposure as well as I expected (or they advertised). Seriously considering using good PV wire this time but not sure if it would do any better. I will probably use the AM Solar combiner box as there does not seam to be any other good alternative that I have found.
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Old 01-04-2022, 06:59 AM   #12
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I have removed the panel you are talking about and was considering coming down into that chase but have not got a good bead on locating it from the roof yet. That black vent pipe must not go straight up so I am afraid I may drill into it not knowing its path yet. I am planning to mount my TX-50 display on the hall side of that chase so it would be nice to route the solar wire with it to the electronics under the bed. Did you use the overpriced AM Solar duplex cable? I used it 4 years ago when I did my series/parallel panel to Airstream prewire junction box install. Honestly it did not hold up to sun/UV exposure as well as I expected (or they advertised). Seriously considering using good PV wire this time but not sure if it would do any better. I will probably use the AM Solar combiner box as there does not seam to be any other good alternative that I have found.
I would get the PV wire. Mine has held up very well to sun. (6 years??). The duplex is not an "outdoor" wire, I don't think. I used 6 ga Marine tinned stranded duplex inside. Very flexible and stands up to vibration very well.
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Old 01-04-2022, 08:19 AM   #13
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Technically a number of solar panels in parallel should have individual fuses at the panel. Code specifies this to be the case when you exceed the individual panel maximum short circuit current which is not always specified. Practically speaking it does make sense that a short in one panel could cause all current from other panels to flow through the wire of that panel and cause a fire. So back of the envelope 4/5 x 100 watt panels could push 30 amps through 10 gauge (or less) wire which might cause a fire. AM Solar says nothing about this and I am thinking they probably don't ever add panel fuses. Anyone here with say 4 or more 100 watt panels have fuses on each individual panel? I am converting from a 2x2 series/parallel array (100 watt panels) with factory pre-wire to a 5 panel parallel array with my own 6 gauge drop and trying to decide it it would be smart to add panel fuses. All opinions and thought experiments on this are welcome!
AM solar sells Zamp solar panels. Each has a fuse on the underside. I just installed 4.
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Old 01-04-2022, 09:26 AM   #14
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Quote:
Originally Posted by OrangeCrush View Post
I have removed the panel you are talking about and was considering coming down into that chase but have not got a good bead on locating it from the roof yet. That black vent pipe must not go straight up so I am afraid I may drill into it not knowing its path yet. I am planning to mount my TX-50 display on the hall side of that chase so it would be nice to route the solar wire with it to the electronics under the bed. Did you use the overpriced AM Solar duplex cable? I used it 4 years ago when I did my series/parallel panel to Airstream prewire junction box install. Honestly it did not hold up to sun/UV exposure as well as I expected (or they advertised). Seriously considering using good PV wire this time but not sure if it would do any better. I will probably use the AM Solar combiner box as there does not seam to be any other good alternative that I have found.
The black vent pipe does make a 90 degree turn once it makes it past the ceiling. I just went straight up with a long drill bit from the chase as I could see I wouldn't hit anything. If you are worried about it, a cheap endoscope will let you peer around in there.

I used PV wire and so far it seems to be holding up to UV just fine.

I use Victron solar controllers (there are two, one for the roof and one for the ground panel) which have bluetooth capability. That meant all I really needed to be able to see is the Victron BMV712 battery monitor. It just has a little CAT5 cable that needed to be routed from the shunt in my electronics bay to the display in the hall. While it would be mildly entertaining to see the solar charge controller performance, there isn’t anything I could do with that information most of the time. On occasions when I care, I fire up the app on my phone.
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Old 01-04-2022, 11:14 AM   #15
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Thanks all for your input.

Fuses
I talked to Zamp and they put them in all their panels now and believe they are a good thing with little or no risk of inadvertently blowing. The head guy at AM Solar believes they are not necessary with only 20V and says Zamp puts them in just to appease people. You be the judge. My take is up to 5 panels they are not necessary but beyond that I think they are a good idea. I will probably add them as I am experimenting with some TI SM7611 smart bypass diodes and may need to protect me from myself on this one.

Wire
Below is a picture of 4 year old AM Solar UV resistant round duplex wire jacket ($3.00/ft). Right side is sunny side up, left was on trailer. I doubt the jacket would make many more years before cracking through. In all fairness, our trailer is parked outside in the intense Colorado sun year round. Thanks for all your inputs as it has helped me decide to go with PV wire next.
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Old 01-04-2022, 11:18 AM   #16
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The black vent pipe does make a 90 degree turn once it makes it past the ceiling. I just went straight up with a long drill bit from the chase as I could see I wouldn't hit anything.
Great! I think I will do the same. I will probably drill as close to the bathroom door inside the chase as possible so I can clear my front panel which is quite a bit more forward than your. I need to do some more measurements before I know this will work.
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Old 01-04-2022, 11:20 AM   #17
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This is the wire I got for interior solar wiring.

https://gregsmarinewiresupply.com/Du...product_id=166

I would not use this on the roof.
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Old 01-04-2022, 03:08 PM   #18
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This is the wire I got for interior solar wiring.

https://gregsmarinewiresupply.com/Du...product_id=166

I would not use this on the roof.
Thanks. That looks like very good stuff for running from roof down.

FYI - AM Solar told me they had a bad batch of roof cable about when I purchased mine. It did not hold up to UV. They are going to warranty replace it so thought I would let everyone know that the pic I showed of 4 year cable jacket should not be the norm for their cable.
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Old 01-09-2022, 01:11 PM   #19
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Technically a number of solar panels in parallel should have individual fuses at the panel. Code specifies this to be the case when you exceed the individual panel maximum short circuit current which is not always specified. Practically speaking it does make sense that a short in one panel could cause all current from other panels to flow through the wire of that panel and cause a fire. So back of the envelope 4/5 x 100 watt panels could push 30 amps through 10 gauge (or less) wire which might cause a fire. AM Solar says nothing about this and I am thinking they probably don't ever add panel fuses. Anyone here with say 4 or more 100 watt panels have fuses on each individual panel? I am converting from a 2x2 series/parallel array (100 watt panels) with factory pre-wire to a 5 panel parallel array with my own 6 gauge drop and trying to decide it it would be smart to add panel fuses. All opinions and thought experiments on this are welcome!
Since your existing array is 2S 2P, then I assume that you have an MPPT controller of some kind. Most of those require a panel Vmp to be at least 4 - 5 volts higher than the V battery to really work at all and 10+ volts is a lot better.

If you switch to a 5 P array and they are typical ~ 18 Vmp type panels, then really consider strongly to also change to a PWM controller like a bogart, as it will turn on with much less light (mornings / evenings / overcast).

It is a trade off in how it will operate. Under non perfect lighting conditions and just a small Vmp - V bat difference like your proposed setup, PWM will operate more hours per day vs MPPT. When lighting is perfect, the the MPPT will be slightly more efficient.

In an array that is setup for 2 x 18 Vmp panels in series, then clearly an MPPT controller is much better than PWM under really any conditions.

If your goal is to add a panel to the existing 2S 2P array and to keep using the existing MPPT controller, then it might be better to try to find a single panel with a Vmp that matches the 2S voltage of the existing array and tie it in that way.
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Old 01-12-2022, 06:32 AM   #20
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Please follow this website on the solar panel fusing. I think that will answer all of your questions.
https://www.explorist.life/how-to-fu...y-not-need-to/

As for parallel/series strings and wire gauge this can get complicated. I did an analysis of this last year creating a calculator that will show the wire losses and efficiency of the system based on numbers that are more true to the solar panel real world using the NOCT rating of the panels. One key takeaway was that wire gauge is absolutely key in parallel systems. You have a whole lot more leeway in series parallel as the VMP is much higher. One thing that my calculator takes into effect is the temperatures that is it operates on and that my calculator uses the calculations for stranded wire versus solid which is what most online calculators will use (also the charts that you get). In any event the solid versus stranded made a small difference (perhaps one wire gauge), but the biggest losses for the panels is temperature. If you are operating on temperatures below 25C which the panel was rated at then you can use most of the panels numbers, but as soon as you go above the 25C mark you need to de-rate the panel. Which also affects your wire losses and your panel losses which all affect your VMP. That is why an MPPT controller is pretty much useless on a parallel system. It will yield good results in the cold but in the warmth not so much. Also, your panel temperature is much higher than the ambient temperature. So this is where the bulk of your losses come from. If you are using series/parallel configurations then you can use the Victron calculator. It works very well although it uses a metric wire gauge and meters for length. I actually took their calculator apart to see how they are calculating things and then changed their calculations to use feet and added AWG as an option as well. It did take a while to break their password protection on the calculator. Lol. In my own calculator I am not trying to achieve what they are, but it was merely an exercise in going through an in depth analysis on parallel and series and how wire gauge and temperature affects the end results in PWM and MPPT efficiencies. If you have the time I encourage you to do some digging on these subjects as well.
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