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Old 18-04-2012, 13:42   #1
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Fuse/breaker question for solar set-up

Hi, getting close with my solar install, have the big parts but need to get the "bits" worked out. I have a question regarding circuit and panel protection.

The scenario:

I'm wiring two 225W Sanyo solar panels in series. Specs per panel are Voc=53V, Isc=5.66A, Vmp= 86.8V, 12ga MC4 connections from panel, switching to 10ga for wiring from panel wiring to MPPT charge controller for minimal V drop (not a big concern anyway with such high voltage). (See pic for other specs).

Since I'm putting them in series, I'll have a Voc=106V, Isc= 5.66A. This will run for about 30 ft (each way) to an Outback 60. The Outback 60 will feed into my power busbar about 5 ft away. I'm going to use a #2 AWG to minimize V drop again here. For overcurrent protection I plan on using a 60A 12V breaker close to the busbar instead of a fuse so I have flexibility to isolate the solar system from the rest of my DC system. I'll probably use this one: MRCB 60, 80, 100, 150 Amp DC circuit breakers with switch

I also want (and think it is required) circuit protection in between my controller and panels, located as near the panels as possible (still probably a 12 ft run to get into the inside of the boat). I'd like breakers, again to isolate the panels from the controller easily in case I need to do open it up.

My question:

For those that are using breakers to isolate their series-wired panels, what are you using? Most DC breakers I've seen are rated up to only 48V or so? I found these from Midnite solar: Midnite Solar MNEPV 150 VDC Solar Array Breakers , and I guess I could put it in this box: Midnite Solar Baby Box Enclosure for 1-4 Din Rail Breakers , but it seems kinda bulky and am guessing there is an easier solution. I'd go with the 15A breaker.

Or do folks just add an in-line fuse and pull the fuse if they need to open up their charge controller? Or do you just use a blanket and hope the wind doesn't blow it away?

Thanks!

Frank
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Old 18-04-2012, 14:09   #2
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Re: Fuse/breaker question for solar set-up

Frank:

As you propose to wire your panels, you don't need any fuse or breaker protection between the controller and the panel. With an Isc of 5.66 amps that is way below the current carrying capacity (Ampacity) of the wire. You could short the wire at the controller all day long and the wire wouldn't care.

But you do need a disconnect at the panels but not necessarily a fuse or a breaker.

A Voc of 106 V can kill you. Your system needs to be wired and protected in conduit (or run behind panels that don't normally open) just as if it were 120V AC.

David
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Old 18-04-2012, 14:20   #3
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Re: Fuse/breaker question for solar set-up

GeoPowers,

A Circuit breaker is fine. Most use a fuse, because it is a lot cheaper.

Single Pole Circuit Breaker

I also used circuit breakers close to the controller to turn off one or both of my panels for when I am testing or on shore power.

Switches and fusses would work also.
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Old 18-04-2012, 18:47   #4
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Re: Fuse/breaker question for solar set-up

Thanks for the replies. I wouldn't mind going the switches/fuses route between the controller and panels, but I haven't found any switches that were for a DC rating of over 106V.

I saw those Blue Sea breakers, but they are only rated to 65V DC.

Looks like the midnite solar breaker might be the best thing out there right now for my setup.

Frank
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Old 18-04-2012, 19:09   #5
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Re: Fuse/breaker question for solar set-up

When it comes to anything electricity there is nothing better, or more important, than SIMPLE. Instead of commenting on my understanding, or lack thereof, of your desired system, I recommend this thread: Solar Panel Circuit Breaker Wiring
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Old 18-04-2012, 19:11   #6
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Re: Fuse/breaker question for solar set-up

GeoPowers,

My SunPower panels put out 48.7 volts each and are wired in Parallel, because one is mounted on my bimini and the other is mounted on my davits.
48.7 volts is all I have to worry about.
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Old 18-04-2012, 20:15   #7
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Re: Fuse/breaker question for solar set-up

I would agree with the above: that since the panels absolutely limit the current to about 5A there is no danger of overloading the wiring. Anyway, the fuse or breaker needs to be near the panel, not the controller, to protect the wire. I don't know what the official reg's are (and don't care). I would not put anything in that circuit.

Breaking of DC circuits with breakers and switches is tough duty because of the potential for severe arcing. Panels are not very inductive so maybe it's not as bad as a motor. But don't cheat on the ratings.
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Old 18-04-2012, 20:43   #8
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The Outback 60 manual shows a "typical" installation with a 60A OCPD on each side of the charge controller. With my system I agree with the 60A breaker between the batts and the controller, but not between the controller and panels. I also think the 60A breaker between the controller and batts will protect all the wiring up to the panels as far as ampacity goes, but for panel disconnect and also to protect the panels themselves I think a 15A breaker at the appropriate voltage rating is prudent.

Frank
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Old 19-04-2012, 06:16   #9
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Re: Fuse/breaker question for solar set-up

Check out Carling Technologies breakers, rated to 60, 80 & 120V DC ➥ Carling Tech: Magnetic Circuit Breakers
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Old 20-04-2012, 05:03   #10
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Re: Fuse/breaker question for solar set-up

Thanks, Gord.
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