PV circuit breaker: single pole vs double pole

SeattleNewbie

2013 NCV3 2500 170" WB
I have my 4x100 watt solar panels wired in series and typically get less than the rated 5.29 amps at between 65-80 Volts. The system works well with my mppt controller and I have no complaints.

I have however been lazy/busy and neglected to install a Circuit Breaker on the wires going from the panels to the mppt controller.

Looking at low voltage DC breakers on Amazon I see some single pole ones and some double pole ones

I was under the impression that double pole breakers are used for 220 volt connections which have two hot wires.

1 Would you please help me understand what the trade offs are between low voltage single pole and double breakers such as these?
https://www.amazon.com/dp/B07KNPCS18
Vs
https://www.amazon.com/dp/B07KNQF4QX


2. What is the appropriate size for such a breaker in my application? 6 amp? 10 amp?
 

calbiker

Well-known member
What’s the purpose of the breaker? It will never trip.

A simple switch works well. That’s what I installed.
 

SeattleNewbie

2013 NCV3 2500 170" WB
Given that you're running 80 volts, are "low voltage" breakers applicable?

--dick
That's also a good question. I don't know.
I see in the Amazon reviews that folks are using these for PVs and that the they seem to be rated for 400V which isn't exactly like as the description says
 

SeattleNewbie

2013 NCV3 2500 170" WB
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hein

Van Guru
Agree with Calbiker that a switch is fine. The only case where a breaker would trip is if there is a failure (short) in the controller. An inline fuse would also work. Or both. You would want a switch rated for DC and 10A. If you do decide on a breaker then it should probably be rated for DC. I believe the contacts are more prone to arcing with DC.

Here is a nice heavy duty fuse holder: https://www.amazon.com/gp/product/B000CZ2Z92

You can make your own by using two female spade connectors: https://sprinter-source.com/forum/showpost.php?p=599486&postcount=916

Another option is MC4 inline fuse holders: https://www.amazon.com/Renogy-30-Waterproof-Line-Holder/dp/B00YG2IAQ4

I used an inline fuse for our solar panels.

All the best,
Hein
DIYvan
541 490 5098
 
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SeattleNewbie

2013 NCV3 2500 170" WB
Agree with Calbiker that a switch is fine. The only case where a breaker would trip is if there is a failure (short) in the controller. An inline fuse would also work. Or both. You would want a switch rated for DC and 10A. If you do decide on a breaker then it should probably be rated for DC. I believe the contacts are more prone to arcing with DC.

Here is a nice heavy duty fuse holder: https://www.amazon.com/gp/product/B000CZ2Z92

Another option is MC4 inline fuse holders: https://www.amazon.com/Renogy-30-Waterproof-Line-Holder/dp/B00YG2IAQ4

I used an inline fuse for our solar panels.

All the best,
Hein
DIYvan
541 490 5098
Thank you. I think I have a couple of these fuse holders left over from other projects.

Are the blade fuses rated for 12/24v though? Will they work when the voltage is higher at 80v ?
 

hein

Van Guru
Thank you. I think I have a couple of these fuse holders left over from other projects.

Are the blade fuses rated for 12/24v though? Will they work when the voltage is higher at 80v ?
Littelfuse makes blade fuses rated at 58V.
https://www.littelfuse.com/~/media/...blade-fuses/littelfuse_maxi_58v_datasheet.pdf

Beyond that you may need to use their high voltage fuses;
https://www.littelfuse.com/~/media/...es/littelfuse_lowcurrenthevfuse_datasheet.pdf

All the best,
Hein
DIYvan
541 490 5098
 

calbiker

Well-known member
Anybody that advocates installing a circuit breaker between a series solar panel and the charge controller doesn't understand the technology. I don't see a scenario where this breaker can trip; this includes any charge controller faults.

Circuit breakers are used if you have a system with 3 or more parallel strings. Each string has its own breaker.

Some people do install a breaker at that location. It's used as an on/off switch, not a breaker. It becomes a pricy switch.

Simple toggle switch
https://www.ebay.com/itm/5X-12V-SPST-Solid-Metal-Toggle-Switch-ON-OFF-Single-Pole-for-Marine-Automotive/333274731386?hash=item4d98b8d37a:g:wwoAAOSwYTpdNyGb



I was reminded of my lack of CB/Switch when looking at the picture here
https://sprinter-source.com/forum/showthread.php?t=83440

It seems like he's just following the Victron recommendation. My Renogy controller's manual doesn't have such a recommendation.

What switch do you use?
 

DavidEM

Member
I totally agree with calbiker. Solar panels are fixed current devices. There is no way that the current will ever exceed its Ioc value, (unless you camp in the astrosphere a lot closer to the sun). Since the current is fixed, it can never cause a breaker to trip, so why install a breaker.

Looking at the other end of the circuit I suppose that there can be two simultaneous failures that could cause a fire: the controller would have to develop a dead short to the battery and the wiring to the panels would also have to short to ground creating a fire situation. A fairly simple way to protect from that is to make sure that the panel wiring has a greater ampacity than the breaker near the battery. That may not work well with the OP's situation with lots of panels hooked in parallel.

David
 

russinthecascades

Active member
Anybody that advocates installing a circuit breaker between a series solar panel and the charge controller doesn't understand the technology. I don't see a scenario where this breaker can trip; this includes any charge controller faults.

Circuit breakers are used if you have a system with 3 or more parallel strings. Each string has its own breaker.

Some people do install a breaker at that location. It's used as an on/off switch, not a breaker. It becomes a pricy switch.

Simple toggle switch
https://www.ebay.com/itm/5X-12V-SPST-Solid-Metal-Toggle-Switch-ON-OFF-Single-Pole-for-Marine-Automotive/333274731386?hash=item4d98b8d37a:g:wwoAAOSwYTpdNyGb
That describes me! Using a BS 7210 15A as an on/off, but it didn't cost too much.
https://shop.pkys.com/Blue-Sea-7210-Single-Pole-Circuit-Breaker-15-Amps-White_p_1632.html
 

Kevin.Hutch

2011 Mercedes 313 906
Given that you're running 80 volts, are "low voltage" breakers applicable?

--dick
Low voltage is defined as below 1000volt, what you are thinking of is Extra Low voltage and the issue is not the voltage but AC or DC. It is a question of the passing the 0-volt point every cycle reduces the arcing. Most low voltage AC breakers are nowadays designed to handle DC at 20% of their AC rating and are not priced differently to robust switches.

An isolator is defined to disconnect the solar power for fault finding and maintenance, some rely on plugs which help isolate a single panel to identify its output.

A double pole switch is to ensure the panel is isolated, although both live wires out of a solar panel should be isolated from the chassis, so a single-pole switch is adequate. Solar panels can be shorted out with no side effect but this requires access to the bare wires.
 

HarryN

Well-known member
I have my 4x100 watt solar panels wired in series and typically get less than the rated 5.29 amps at between 65-80 Volts. The system works well with my mppt controller and I have no complaints.

I have however been lazy/busy and neglected to install a Circuit Breaker on the wires going from the panels to the mppt controller.

Looking at low voltage DC breakers on Amazon I see some single pole ones and some double pole ones

I was under the impression that double pole breakers are used for 220 volt connections which have two hot wires.

1 Would you please help me understand what the trade offs are between low voltage single pole and double breakers such as these?
https://www.amazon.com/dp/B07KNPCS18
Vs
https://www.amazon.com/dp/B07KNQF4QX


2. What is the appropriate size for such a breaker in my application? 6 amp? 10 amp?
The label on the breakers indicates that they are for AC use - not DC.

There are breakers that are rated for both DC and AC use. The AC portion is the "easy" part. Breaking a DC circuit at even a modest 80 volts can be... "Exciting"
 

Kevin.Hutch

2011 Mercedes 313 906
The point of a circuit breaker or fuse for that matter is to protect the wiring and should be specified accordingly. In the case of solar output, it's short circuit current should be lower than the cable spec to minimize voltage drop and as such a short should never provide enough current to operate a circuit breaker making circuit protection redundant.

Isolation is another issue, be it circuit breaker, switch or plug, be sure it is suited for isolating the maximum current possible out of the solar array without arcing excessively.

Having said this a breaker will only be used as a switch and as it will rarely be switched its shortcomings for isolating a DC circuit are unlikely to surface.

Double pole switching is always better than single-pole but rarely called for or justified if it is a quality permanent installation.
 

Snoops

New member
Agree with what others have said here as an Electrician and Solar Installer - solar panels cannot generate any fault current and won’t get above their rated current even under perfect conditions, so there’s no chance of them damaging the cables. In fact, it is quite safe to short a solar panel out indefinitely and this is how you test them as well so a breaker is not necessary, I’d just use a switch as an isolator which is all that’s used in domestic installations as well.
 

SSTraveler

2014 LTV Unity Murphy Bed
If you want to go with a circuit breaker vs a fuse, Amazon has some low amp 80vdc rated circuit breakers, https://www.amazon.com/dp/B07MZPKG89/ref=twister_B07PGRG773?_encoding=UTF8&psc=1 or https://www.amazon.com/Tocas-Hydrau...=80v+dc+circuit+breaker&qid=1582804024&sr=8-2 or https://www.amazon.com/dp/B000MMDLPM/ref=twister_B01MQD1FE5?_encoding=UTF8&psc=1. A single pole 10a CB would be your best option placed in line on the positive wire. I used CBs as well, they serve the dual purpose of providing and on/off switch making it very easy to disconnect the solar before I need to disconnect my batteries. You can burn up a solar controller if you don't disconnect the panel input before disconnecting the batteries.
 
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