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Old 01-11-2018, 09:42   #1
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Circuit Breaker on Solar system

Dear all, thank you in advance to anybody helping and sorry for my english.
Just completed the installation of my pv system on my boat.
So far it is like that:

Pv standard module 275wp (V=32V and I=9A)
4sqmm wiring to the solar charger (approx awg 12)
20A Mppt solar charger
10sqmm wiring to 300ah battery bank (approx awg8).
I put a 30A fuse on the positive wire from the charger to the batteries.

Now my question. I'd like to add a protection and a switch on the line from the solar panel to the charger.
I found this on amazon that looks more sexy than the "industrial ones" mounted on the DIN guide and can be easily mounted without too many holes.
The 20A current is ok (maybe 16 would be more appropriate) but it claims "12-24V".
My question is, being a single pole device (only the positive wire is connected) and being only sensitive to current (i think) may i have any problem in connecting it to my 32V solar panel? I found similar products up to 50V, but in this case only for currents above 30A.

Any suggestion?

Thank you!

https://www.amazon.it/dp/B074RJR1JT/..._UCY2BbNDQS66F
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Old 01-11-2018, 14:34   #2
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Re: Circuit Breaker on Solar system

You should have a fuse or breaker, located as close to the panels as practical. The voltage rating needs to be more than the peak Open circuit voltage of the panels, plus 15%. Under solar edge conditions, thatís what you will see. My guess it that you will be looking at something in the 60V range.

You also should have fuses or breakers between the charger and battery at BOTH the charger and and the battery end. Both are power sources, so you need to protect both from dumping unlimited current into the wiring.

Now you can cut whatever corners you choose to cut.
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Old 01-11-2018, 14:55   #3
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Re: Circuit Breaker on Solar system

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You should have a fuse or breaker, located as close to the panels as practical. The voltage rating needs to be more than the peak Open circuit voltage of the panels, plus 15%. Under solar edge conditions, thatís what you will see. My guess it that you will be looking at something in the 60V range.

You also should have fuses or breakers between the charger and battery at BOTH the charger and and the battery end. Both are power sources, so you need to protect both from dumping unlimited current into the wiring.

Now you can cut whatever corners you choose to cut.
I'll disagree here... going in a direction people who work with me would be surprised, since I am always pointing out places where fuses should be ADDED...

There is no need for a fuse at the panel end of the circuit. The reason is that the panels are intrinsically limited to a maximum power output. The wires (of course!) need to be sized to handle that much power (and a bit more.) There is NO scenario under which a solar panel can output more amps than it is designed to.

There is absolutely a need for over current protection at the battery end, because in the event of a failure the batteries can supply more than enough current to melt whatever wires you install.

And by the way.... fuses and breakers are sized by AMPS they interrupt, NOT by volts...
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Old 01-11-2018, 14:57   #4
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Re: Circuit Breaker on Solar system

I just used a standard 20 amp double pole switch for the panel disconnect. Wired an in line fuse before the switch. Whatever the amps are for your panels, size the fuse based on that. The fuse to the battery should match the controller, in your case sounds like 20 amps.
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Old 01-11-2018, 15:08   #5
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Re: Circuit Breaker on Solar system

Quote:
Originally Posted by tanglewood View Post
You should have a fuse or breaker, located as close to the panels as practical. The voltage rating needs to be more than the peak Open circuit voltage of the panels, plus 15%. Under solar edge conditions, thatís what you will see. My guess it that you will be looking at something in the 60V range.

You also should have fuses or breakers between the charger and battery at BOTH the charger and and the battery end. Both are power sources, so you need to protect both from dumping unlimited current into the wiring.

Now you can cut whatever corners you choose to cut.
This advice is actually contrary to that offered from morningstar (the manufacturer of the controller that I use) and other reputable suppliers and installers of this type of equipment.
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Old 01-11-2018, 15:40   #6
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Re: Circuit Breaker on Solar system

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I'll disagree here... going in a direction people who work with me would be surprised, since I am always pointing out places where fuses should be ADDED...



There is no need for a fuse at the panel end of the circuit. The reason is that the panels are intrinsically limited to a maximum power output. The wires (of course!) need to be sized to handle that much power (and a bit more.) There is NO scenario under which a solar panel can output more amps than it is designed to.



There is absolutely a need for over current protection at the battery end, because in the event of a failure the batteries can supply more than enough current to melt whatever wires you install.



And by the way.... fuses and breakers are sized by AMPS they interrupt, NOT by volts...


Point taken on the solar panel end of things. But for land implementations NEC still requires the breaker/fuse. On boats Iím not aware of any particular guidance.

Re the battery end of things, if you want to use the wire as the fuse, OK, but thatís generally frowned on as a practice.

I agree that circuit protection is bas d on current, but it is always current up to a certain voltage limit. Itís all about arcing and welding of contacts, and particularly challenging for DC where there is no zero voltage crossing to self extinguish the arc. The breaker (or fuse) would be selected for the desired current rating, but absolutely needs to also meet to voltage rating of the circuit
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Old 01-11-2018, 15:42   #7
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Re: Circuit Breaker on Solar system

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This advice is actually contrary to that offered from morningstar (the manufacturer of the controller that I use) and other reputable suppliers and installers of this type of equipment.


What do they recommend? Trying to understand where we differ.
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Old 01-11-2018, 15:50   #8
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Re: Circuit Breaker on Solar system

I thank everybody who gave his contrubution so far (and in advance orhers that may follow).
I am pretty sure that from the SC to the batteries, the fuse should be sized on the wiring and not on maximum output of the SC.

My doubt is about the circuit breaker from the pv module to the SC (the reason why i am insisting on the CB rather than a fuse is because i want to have the possibility to switch off the pv panel with the CB if i need it). In particular i do not understand why a single pole circuit breaker (like the one i found on amazon) should be rated on voltage, besides obviously the max amperage. From some of the above comments i have understood that only amperage should be considered. And that makes sense to me. Of course i would be happy to have different opinions to understand what i am missing (if there is anything missing....).
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Old 01-11-2018, 15:54   #9
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Re: Circuit Breaker on Solar system

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Originally Posted by tanglewood View Post

I agree that circuit protection is bas d on current, but it is always current up to a certain voltage limit. Itís all about arcing and welding of contacts, and particularly challenging for DC where there is no zero voltage crossing to self extinguish the arc. The breaker (or fuse) would be selected for the desired current rating, but absolutely needs to also meet to voltage rating of the circuit
I did not read this comment from you before writing my last msg.
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Old 01-11-2018, 17:53   #10
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Re: Circuit Breaker on Solar system

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Originally Posted by Achab65 View Post
I thank everybody who gave his contrubution so far (and in advance orhers that may follow).
I am pretty sure that from the SC to the batteries, the fuse should be sized on the wiring and not on maximum output of the SC.

My doubt is about the circuit breaker from the pv module to the SC (the reason why i am insisting on the CB rather than a fuse is because i want to have the possibility to switch off the pv panel with the CB if i need it). In particular i do not understand why a single pole circuit breaker (like the one i found on amazon) should be rated on voltage, besides obviously the max amperage. From some of the above comments i have understood that only amperage should be considered. And that makes sense to me. Of course i would be happy to have different opinions to understand what i am missing (if there is anything missing....).


Our posts probably crossed in the ethos.

The reason voltage matters is because of extinguishing the arc created when a breaker is opened or closed under load.

With AC itís much easier because the voltage goes to zero and the arc self extinguished twice a cycle, so every 25th or 30th of a second depending on where you are in the world. So you will typically see switches and breakers rated for much higher AC voltage than DC.

With DC there is no zero voltage and no self extinguishing of the arc. This makes higher voltage DC switches and breakers much harder to make, and often much more expensive as voltages go up. At higher solar voltages like 600V you will see fuses much more often for this reason rather than breakers.

If you use a switch or breaker that is under rated on voltage, you risk welded contacts and an inoperative device.
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Old 01-11-2018, 18:19   #11
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Re: Circuit Breaker on Solar system

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Originally Posted by tanglewood View Post
What do they recommend? Trying to understand where we differ.
Morningstar and victron instructions for their PWM controllers say that the controller should be installed as close as possible to the battery with a fuse installed within 7 inches of the battery. They do not advise the installation of another fuse (or circuit breaker) between controller and panels with at least one I have read actually advising against it. If the need is felt that there should be a switch to enable the disconnect of the panels ( I can't imagine why ) then I would guess that a double pole switch of the required amperage or above would do the job.
I am of the belief that when one properly installs a suitable solar system sized to do the job then it should be left to do that job without undue interference. Done properly they operate for years without interference.
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Old 02-11-2018, 06:51   #12
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Re: Circuit Breaker on Solar system

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Morningstar and victron instructions for their PWM controllers say that the controller should be installed as close as possible to the battery with a fuse installed within 7 inches of the battery. They do not advise the installation of another fuse (or circuit breaker) between controller and panels with at least one I have read actually advising against it. If the need is felt that there should be a switch to enable the disconnect of the panels ( I can't imagine why ) then I would guess that a double pole switch of the required amperage or above would do the job.

I am of the belief that when one properly installs a suitable solar system sized to do the job then it should be left to do that job without undue interference. Done properly they operate for years without interference.


Thanks. They are probably applying the same logic a for the panel connection, namely the current delivery capacity is inherently limited, so fusing not required if the wires can handle the limited current.

I wonder if NEC has changed this since I last looks.

ABYC creates a similar puzzle. For a battery charger, ABYC requires fusing at both the charger and battery since both are power sources. By extension, this applies to solar as well. The more complete installations I have are do all the fusing. There is little down side to it other than cost.

Iím not sure ABYC says anything particular to solar, but I also havenít gone looking specifically.
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Old 02-11-2018, 07:42   #13
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Re: Circuit Breaker on Solar system

A fuse between the solar controller and the batteries is essential.

There is some confusion about the need to fuse between the controller and the panels. It is often stated that a fuse here is never needed because the solar panel current can never exceed the wire’s rating. This is only partially correct. The solar panel current cannot exceed the external wire’s rating, but it can in some fault conditions exceed the rating of the internal wires within the solar panel. This can potentially start a fire.

Hence, all solar panel manufacturers recommend a fuse, or circuit breaker, between the controller and the panels, in addition to a fuse or circuit breaker between the controller and the batteries.

You can calculate if a fuse or fuses is really needed, but it is complicated. There are some rough rules of thumb based on the number of connected panels, but I am reluctant to repeat these, as they are not always foolproof. It is also important to install the fuse in the correct place.

If you do this, please make sure the DC voltage rating of the fuse or circuit breaker is greater than the maximum voltage that can be produced by the panels. Don’t assume a device with a very high AC voltage rating will be fine with a much lower DC voltage. The wrong fuse or circuit breaker between the panel and the controller can be more dangerous than no protection. If you have high voltage panels remember that above 50v DC can be lethal.
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Old 02-11-2018, 08:51   #14
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Re: Circuit Breaker on Solar system

For those interested, I found this article that is a nice blend of a technical disussion and something that can be read by the average person:

http://ep-ru.mersen.com/fileadmin/ca...Tech-Topic.pdf
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Old 02-11-2018, 16:36   #15
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Re: Circuit Breaker on Solar system

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There is absolutely a need for over current protection at the battery end, because in the event of a failure the batteries can supply more than enough current to melt whatever wires you install.

And by the way.... fuses and breakers are sized by AMPS they interrupt, NOT by volts...
1) red hot wires are what cause a fire. to assume they'll vaporize before they start a fire is at best wishful thinking. then there's also the issue of then having to rewire the circuit even if you don't cause a fire.

2) fuses and breakers are also specified by voltage. the voltage spec is related to electrical arcing.
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