Wiring sizes, disadvantage to larger?

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bluewickedburner
bluewickedburner Solar Expert Posts: 78 ✭✭✭✭
in Solar Beginners Corner #1
My first round is 3 100 watt panels in parallel going to a Midnight Classic 150 controller. Yes, I know the Classic is overkill but I'll be adding more panels and there are other features of it I just want to have. Each panel is fused and there is a 90 amp fuse between the breaker box and the controller (or plans to be)

I'm thinking about using #6 stranded from the roof mounted combiner (motorhome) down to the controller. Is there a disadvantage to using the larger dia #6 as opposed to a lesser gauge wire?

The distance I'm talking about is about 15 feet total. From the charge controller to the batteries will be about 4 feet where I will use at least #000.

I have #0000 running from the batteries to the Inverter/charger (2000 watt).

12 volt system, 4 6 volt batteries with 720 amp @ 20 hrs.

There will eventually be a total of about 1300 watts of panels on the roof.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Wiring sizes, disadvantage to larger?

    Disadvantages to using larger-than-necessary wire:

    #1. Costs more.
    #2. May not fit in connectors.

    That's about it.

    If the panels are wired in series (the Midnight can take very high input Voltage) the current would be the same as one panel. 6 AWG is definitely overkill for less than 10 Amps current potential, and only 15 feet of distance.

    Even quadrupled you get less than 40 Amps, and really 10 AWG is about all you'd need.

    Your 4/0 is over-sized too, but I wouldn't change it.

    Someone else might have a different opinion.
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  • bluewickedburner
    bluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    #3
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    Re: Wiring sizes, disadvantage to larger?

    Thanks for that. I happen to have the wire already in quite a few sizes so either way the costs would be the same. I don't have enough to sell off though.

    I'm going down through the roof and once it penetrates there is a short of in-between wall area between two rooms. The wire would just sort of hang there (I can't get into that space other than fish it) but I was thinking about using conduit so to keep it somewhat rigid and from banging around. I could drill holes in the walls and manage some hold downs but that seems kind of messy.

    From there the wire will go through an already existing floor penetration where other electrical system wires go. Next is into a bay next to the battery bay. The bay the charge controller will reside in is sealed but I'm adding some convection ventilation with a back up fan for active ventilation if temperatures get above 90 F.

    I saw some liqui-tight (or something similar sounding, gray in outside color) and some plastic and was going to use one of them. I'd rather go better than just okay. Any comments on that? I'm measuring three times before cutting and am at the point of throwing the materials list together for that part.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Wiring sizes, disadvantage to larger?

    Could you fish some flexible conduit through that inaccessible space? Some armour around the wires in case it bangs into something you can see which happens to be sharp, pointed, and connected to ground (like the business end of a machine screw).

    I don't do RV's. And I have a great dislike of putting holes through any roof. Too many years of fixing holes in roofs I guess. :p But there are some guys on here who have done this sort of thing successfully. They'd probably know how best to keep the water out.
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  • bluewickedburner
    bluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    #5
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    Re: Wiring sizes, disadvantage to larger?

    There is a small 5 watt panel on the roof that came with the MH for keeping with the normal discharge of the AMG engine batteries. The ran the wire from that down through so I was going to use the same path. Since the hole is already there I was going to use it, just open it up a bit.

    My plan is to put a weatherproof box there (small pelican case or similar) over the hole and seal it in place. The conduit could start out (going down) from there so I can seal that with Silka or Dicor sealant). Then it is a straight shot down which I can fish and get the conduit to the top of the storage bay, going through the stop and likewise being sealed there. That way I'd have a sealed (around circumference) conduit through which I can easily send down the panel wires to the breaker and onto the charge controller.

    The conduit is 2: diameter. I also want to run some wires up to the roof for cameras at each of the 4 corners looking down for a sort of poor mans packing assistance and security system. As I added more panels I want to avoid any heating issues in the conduit. The wire going up will carry power over ethernet for the wireless cameras. Pretty low voltage stuff.

    Those cameras will be supplied power via an isolated AGM deep cycle battery maintained by a 50 watt panel on the roof.
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  • SCharles
    SCharles Solar Expert Posts: 123 ✭✭
    #6
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    Re: Wiring sizes, disadvantage to larger?
    bluewickedburner wrote: »
    My first round is 3 100 watt panels in parallel going to a Midnight Classic 150 controller. Yes, I know the Classic is overkill but I'll be adding more panels and there are other features of it I just want to have. Each panel is fused and there is a 90 amp fuse between the breaker box and the controller (or plans to be)

    I'm thinking about using #6 stranded from the roof mounted combiner (motorhome) down to the controller. Is there a disadvantage to using the larger dia #6 as opposed to a lesser gauge wire?

    The distance I'm talking about is about 15 feet total. From the charge controller to the batteries will be about 4 feet where I will use at least #000.

    I have #0000 running from the batteries to the Inverter/charger (2000 watt).

    12 volt system, 4 6 volt batteries with 720 amp @ 20 hrs.

    There will eventually be a total of about 1300 watts of panels on the roof.

    Since you are only running fifteen feet, the 6 ga. is more than adequate, but I'd be using that gauge, too. The critical part is batteries to inverter, and you have that covered with heavy cable, which is just right.

    I even have my panels wired together with 6 ga., and we're talking 15" or so between terminals on the smaller panels. I happened to have a bunch of 6 ga. lying around at the time. The larger gauges are stiffer and take a bit more work to run around and through openings and so on. The lugs and connectors are also more difficult to find around my area, any ga. larger than 10 you can forget it, Home Depot and Lowe's don't carry them and I have to order online and wait. Not a huge deal, but inconvenient.

    My combiner boxes, circuit breakers, controllers, and inverter all readily accept larger ga wire, no problem.

    You could get by with smaller ga. wire between panels and from panels to controller, but with only a few feet to run, you are saving very minor money to go with smaller ga. just because it is less expensive per foot. You are doing fine.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
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    Re: Wiring sizes, disadvantage to larger?

    it is critical between the classic and the batteries too as voltage drops could fool the cc into thinking the batteries are farther along than they are.

    as to the large wire i say keep it as you indicate you plan on expanding later. any extra pvs plus your present ones could be sent to a combiner and different voltage configurations (more series voltage) on the pvs too can help in an expansion on the pvs. planning ahead is a good thing to avoid wasting what you already purchased.
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