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Old 27-06-2010, 08:48   #1
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Fuse Each PV Panel Before the Voltage Regulator ?

I'm starting to brainstorm about the eventual install of 4x130W PV panels on our vessel. Proabably the most common way to wire them is in parallel at the panels and then run larger wires to the voltage regulator.

A fellow sailor/friend said I should really look into running separate wiring for each PV panel all the way to somewhere near the voltage regulator but fuse each one of them before combining them in parallel and then on to the voltage regulator.

I guess this would be nice if one panel got damaged somehow and one needed to just disconnect easily.

Feedback, thoughts?

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Old 27-06-2010, 12:02   #2
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I think that your friend doesn't understand the purpose of a fuse. Fuses do two things: 1) they protect the wire from overcurrent that could melt the insulation and start a fire and 2) they protect the appliance (motors, etc) that they serve.

Since a PV panel can't be harmed by current that it generates and most have blocking diodes, the only purpose of a fuse is to protect the wire. The fuse needs to be sized to match the ampacity of the smallest guage wire in the circuit. The overcurrent is comming from the battery that it feeds not the panels.

Your 4x130 panels can generate about 30 amps of current combined in parallel. So I would wire each panel together with 12 guage and then wire to the controller with 8 guage. 12 guage is good for 45 amps so a 40 amp fuse near the battery will protect it.

If your controller will accept a high voltage input- 40 volts or double the open circuit voltage of your panels, then you can save a bit on wiring cost by wiring the panels in series/parallel so that double the single panel voltage is supplied to the controller. Then your current is cut in half and you can wire the panels with 14 guage and make the home run 10 guage.

Increase the guage of the home run if it is longer than about 30 ft round trip to minimize voltage drop and power loss.

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Old 27-06-2010, 12:10   #3
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David, that was my thinking at first as well. However, picture a short to ground on one of the wires from a panel. Now you have the other 3 panels shorted to ground through just one wire. The wires should be sized so that they will each handle the max. current of a single panel without overheating and fused so that if the current exceeds that limit the fuse will protect the wire.
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Old 27-06-2010, 15:15   #4
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I think commonly acceptable practice is to fuse the item as close to the item as possible. And that, to me, is at the output of the panel. It can be a bear to seal from the elements but can be done.

Wiring #12AWG between the panels is fine as it's rated for 45A [url][/url] and running #8 would be fine for a run up to about 20' (assuming a 3% line loss max).

My biggest concerns for the #8 is: does it fit into the controller connections without modification; can you get a connector that'll support that size wire for a reasonable price? If not, then you may want to consider bringing multiple smaller sized wire runs down from the panel.
Capt. Douglas Abbott
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fuses, regulator

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