sunshine_eggo
Happy Breffast!
Then 2X 6mm, each with a suitable fuse.
Help in determining what happens when you have solar panels wired in series then paralell? (4S4P) to end volts and amps at bus bar?
- Thread starter micko
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Then 2X 6mm, each with a suitable fuse.
Oh ok. Thanks so much for clarifying. I did have a guy install the solar system. Well, its not finished, I have taken over as there are too many mistakes and I am having to redue a lot of it. but, this is not my expertise. So, trying to learn as fast as I can. Really appreciate your help ;-)
sunshine_eggo
Happy Breffast!
More importantly, that means the wire is rated for at least 100A. 1.25X 100 = 125A, so that's in the specified range.
I will never get over 55 amp from my solar panels. I have a 160 breaker here, but, max from victron is 140a. I rang my elecectrial wholesaler, they do not carry any type of fuse in the 120 to 140a range. So might have to see if I can get something online withing that range.
Also, going back to that line coming from the bus bar to the victron charger, what size fuse do you think I need on that. Amps will be around 55 amp at best case.
I am running 35mm2 cable from charger to batteries.
I will get a 125A NH00 Fuse for the battery. thanks once again for your help ;-)
sunshine_eggo
Happy Breffast!
Fuses/breakers protect wires not equipment.
There are circumstances where the battery could short to the PV circuit, thus you would have battery dumping current into your array.
Your PV wires between bus bar and MPPT MUST be able to handle at least 55A, and you must have a fuse/breaker to protect that wire. 1.25X 55A, round up to nearest common size.
You are risking a fire. Default 35mm^2 equivalent in the U.S. is NOT rated for 100A.
You must have wire rated for 100A.
You have 16 * 440W = 7040W on your 250/100. It is over-paneled and will never output more than 5900W @ 59V.
This is why you need 120-140A fuse/breaker.
I am not familiar with that brand, but it would work IF it's a quality brand.
Every circuit in the system should have wiring rated for the peak current and a fuse/breaker 1.25X the wire rating.
You are risking a fire. Default 35mm^2 equivalent in the U.S. is NOT rated for 100A.
the 35mm2 cable I have is rated to 188A.
I just spoke to a solar place, told them what I have, they said it is fine to put a 125A breaker between the mppt 250/100 charger and batteries running 35mm2 wire. They sell this charger. But, it makes sense what you are saying.
You must have wire rated for 100A.
You have 16 * 440W = 7040W on your 250/100. It is over-paneled and will never output more than 5900W @ 59V.
This is why you need 120-140A fuse/breaker.
yes, I have over paneled my system. And yes, the victron will only pull in 5800w max. So the 125A fuse between battery and charger will be fine.
Thanks once again.
Your PV wires between bus bar and MPPT MUST be able to handle at least 55A, and you must have a fuse/breaker to protect that wire. 1.25X 55A, round up to nearest common size.
Yes, thanks, I will do this ;-)
The 4mm2 wire is rated to 57A at 140F.
ELECTRICAL CHARACTERISTICS
Voltage Rating
EN50618 & IEC62930 AC: 1.0/1.0kV; DC: Max.1.5kV
Ambient Temperature -40°C up to 90°C
Insulation Resistance At 20℃ ≥ 709 MΩ.km
Current carrying capacity AT 60℃ 57A
Spark test 10000 VAC
Voltage Withstand 6500 VAC
Conductor Resistance AT 20℃ ≤ 5.09 Ω/km
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I would like to know why, if the fuse is for protection of the wire, one would not choose a fuse of equal or even lesser rating to that of the wire? Why not let the fuse be the weak link in place of the wire? Would there be anything wrong with underrating the fuse?
sunshine_eggo
Happy Breffast!
Metric wire ratings are dramatically different than AWG ratings. 60°C 4mm^2 wire isn't even rated for 30A on NEC tables. Have you checked your voltage drop?
Fuses/breakers should be run at no more than 80% of their rated current, or they will "nuisance" blow.
Worth noting that when an over-current situation happens, it's never simply a few or a dozen amps above rated. It's usually a dead short that causes dramatically higher current than rated.
You can always oversize your conductor and put on a lower rated fuse/breaker, but it should not be run at > 80% rated, e.g., you could put 200A wire on a 100A circuit and fuse for 125A.
Here is the info on the 4mm2 cable I have.
Your PV wires between bus bar and MPPT MUST be able to handle at least 55A, and you must have a fuse/breaker to protect that wire. 1.25X 55A, round up to nearest common size.
So, even though I have each PV series fused just before going onto the bus bar, I need another fuse after the bus bar on the line going from the bus bar to the victron charger?
So, could you check to see if I have this correctly. From the bus bar to the charger, pos only. 55.44A X 1.25 = 69.3A. So, I would need a 70A breaker on this line? Like this one?
So, even though I have each PV series fused just before going onto the bus bar, I need another fuse after the bus bar on the line going from the bus bar to the victron charger?
So, could you check to see if I have this correctly. From the bus bar to the charger, pos only. 55.44A X 1.25 = 69.3A. So, I would need a 70A breaker on this line? Like this one?
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I still wonder why a 100A wire that was overloaded to, say, 400A of current, quickly blowing the 125A fuse would not already have overheated enough to increase its internal resistance, potentially causing more problems down the line. If the Max. load is 100A, and one wishes to use a 125A fuse to avoid nuisance trips, I would think the wire should be rated at 125A or better.
Perhaps this is why I'm planning to use 6mm wire when technically 4mm should suffice. I want my conductors running cool--and being in a hot climate where the wire gets an atmospheric head-start on the temperature climb, this seems the more reasonable.
sunshine_eggo
Happy Breffast!
I have no idea what you mean by this. The WIRE in a 100A rated conductor can handle absurd current. It's the insulation material that limits wire temperature and thus its ampacity.
Heating of wire takes time. 500A through a 100A conductor for a fraction of a second isn't going to raise the temperature substantially.
You could certainly do this.
While all of what you said may be true, in my experience with state electrical codes, breakers for wiring circuits were never to be at greater amperages to the rating of the wire gauge. If the wire was rated for 20 amps, one could not put a 30 amp breaker on it. That's why I'm struggling to understand this "solar math." Does it not follow the same codes?
sunshine_eggo
Happy Breffast!
The 1.25X is consistent with NEC requirements.
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