This weekend, weather permitting I'm hoping to install 5 100 watt solar panels on the roof of my fifth wheel. The controller I'll be installing is a Bogart SC-2030 working in conjunction with a trimetric 2030. I have 10 AWG wiring I'll be running to a junction box on the roof for a parallel connection, then drop down to the battery compartment using either 6 AWG wiring on 4, depending on the route I'm able to take and how long that ends up being. My initial thoughts were to fuse each panel using a small automotive fuse block and 7.5amp fuses in the junction box, but now that I'm thinking about it, is there any reason to do this? Looking over the panel specs, the short circuit output for the panels isn't much more than the normal nominal output which would more than likely result in any fuse I used that would handle the normal max output not blowing even if my wiring shorted straight to ground. Are there any gains to be had that I'm not thinking about? I'll put a switch in line between the panels and charge controller so that I can isolate it if desired, and I'll fuse the output side of the controller as I can see where there could be issues there a fuse would provide protection for.I'm open to thoughts, ideas, or lessons learned by others the hard way.

Searching_Ut wrote: My initial thoughts were to fuse each panel using a small automotive fuse block and 7.5amp fuses in the junction box, but now that I'm thinking about it, is there any reason to do this?Not that I've ever considered.

I dont think its neededi have almost 700w my fusing is at the input to the controller,NOT on each panel

MrWizard wrote:I dont think its neededi have almost 700w my fusing is at the input to the controller,NOT on each panelI guess my primary question is why fuse the input side of the controller at all. If the fuse is sized large enough to handle the peak power output of the panels, it will more than likely be large enough it won't blow even with a dead short. There isn't really any "Current pool" waiting in solar panels to dump in the case of a short like there is in a battery, or other type power supply. Being a PWM type controller, when the batteries demand it, the controller pretty much passes full panel output straight to the batteries anyway with the possible current flow going up less than an additional amp per panel under dead short when you take the battery resistance out of the circuit. On the output side of the controller, you could get a large current flow from the battery back to controller if something shorted in the controller, so it makes sense to me to fuse there, I just can't envision any situation on the solar panel side of the circuit where a fuse would protect anything, or add any safety to the circuit.

Searching_Ut wrote:I guess my primary question is why fuse the input side of the controller at all. I don't know such a reason. For a convenience, you may have just a switch on the input side, in case if you need to work on the controller. On the controller output you need a fuse or breaker.

From the Rogue MPT-3048 Manual wrote:Pursuant to National Electric Code requirements (and others which may have jurisdiction in your locale), disconnects and/or overcurrent protection devices are required for both the input and output of the MPT-3048. It is recommended that the PV overcurrent protection device be rated for 30 amps to comply with NEC requirements.So, as I wanted a switch anyway on the solar inputs to the controller, I used a 30A breaker. It's right next to the breaker controlling output going to the batteries.No idea why NEC wants it.

Fusing Solar Installation | Good Sam Community

14 Replies

Almot
Explorer III
Apr 27, 2016
Searching_Ut wrote:

I guess my primary question is why fuse the input side of the controller at all.

I don't know such a reason. For a convenience, you may have just a switch on the input side, in case if you need to work on the controller. On the controller output you need a fuse or breaker.
Searching_Ut
Explorer
Apr 27, 2016
MrWizard wrote:
I dont think its needed
i have almost 700w my fusing is at the input to the controller,
NOT on each panel

I guess my primary question is why fuse the input side of the controller at all. If the fuse is sized large enough to handle the peak power output of the panels, it will more than likely be large enough it won't blow even with a dead short. There isn't really any "Current pool" waiting in solar panels to dump in the case of a short like there is in a battery, or other type power supply. Being a PWM type controller, when the batteries demand it, the controller pretty much passes full panel output straight to the batteries anyway with the possible current flow going up less than an additional amp per panel under dead short when you take the battery resistance out of the circuit. On the output side of the controller, you could get a large current flow from the battery back to controller if something shorted in the controller, so it makes sense to me to fuse there, I just can't envision any situation on the solar panel side of the circuit where a fuse would protect anything, or add any safety to the circuit.
MrWizard
Moderator
Apr 27, 2016
I dont think its needed
i have almost 700w my fusing is at the input to the controller,
NOT on each panel
2oldman
Explorer II
Apr 27, 2016
Searching_Ut wrote:
My initial thoughts were to fuse each panel using a small automotive fuse block and 7.5amp fuses in the junction box, but now that I'm thinking about it, is there any reason to do this?
Not that I've ever considered.

Forum Discussion

Fusing Solar Installation

14 Replies

About Technical Issues

Related Content

Solar Install

Inverter install

Another solar question.

New Solar Install

Truck Camper A/C instalation