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Question regarding fuse board

  • 04-10-2022 2:36pm
    Registered Users Posts: 3,096 ✭✭✭

    The main fuse board is in the house but there is a smaller one in a shed fed from the main one.

    Does a solar pv system need to be wired to the main fuse board? I'm thinking the shed is behind the house so wiring would be out of sight


  • Registered Users Posts: 2,228 ✭✭✭bullit_dodger

    It depends is the best answer people here can give you. The main issue is the guage (thickness) of the cable supplying the secondary small fusebox. Your inverter for the solar panels can output 6kw, and that requires a fairly sizeable cable going back to the main fuse box. You could burn out your exissting cable and potentially start a fire if it's not rated for the current.

    A spark would be able to tell easy enough, but I suspect you'll be routing a new seperate cable back to the main fusebox

  • Registered Users Posts: 1,824 ✭✭✭Markus Antonius

    I also have this exact same question and am hopeful that because the shed fusebox is catered especially for electrical equipment that it would be able to handle solar too, but probably best to get a sparky to confirm.

    If everything above board though, all the household appliances/grid would then draw from the shed fusebox via the main fusebox on sunny days I gather?

  • Moderators, Home & Garden Moderators Posts: 4,486 Mod ✭✭✭✭graememk

    My Inverter is 2 consumer units away from my main consumer unit.

    I do have 16mm2 going to them though.

    Main consumer unit - Meal Shed consumer unit - Barn consumer unit - Solar inverter.

    Its a straight inverter, no batteries so I didnt have to run CT's back to the main grid.

    I know some installers are using a wireless transceiver (LoRA i think, Its transmitting the RS485 signal, not Raw CT signal) if they cant bring back a cat 6 cable for hybrid inverters.

    The grid tie inverters always try to slightly exceed the grid voltage so anything that is not used by the house, is exported/put into batteries.~

    House always gets priority.

  • Moderators, Sports Moderators Posts: 17,889 Mod ✭✭✭✭slave1

    16mm2, lol, future proofing!!!

  • Registered Users Posts: 3,096 ✭✭✭Ginger83

    My issue is that the front of the house faces almost south but it's an old building with thick stone walls. Getting cables back to the main board would be a nightmare and they would be seen.

    If we considered a smaller system the panels might possibly fit on the shed roof (southwest) and then put everything in the shed.

    The fuse board in the shed currently runs power for light, socket, kerosene burner, water softening system and robot lawnmower.

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  • Moderators, Home & Garden Moderators Posts: 4,486 Mod ✭✭✭✭graememk

    I not digging up the street again, Have a couple of cat6 over there too.

    Also have a 2*2.2kw motors on a crusher down there, so we needed the extra power (you should see the current spike when they start, even under no load, about 100amps for a split second)

    All depends on what cable size going out there.

    Its likely only a 2.5mm2 cable, esp if its an old building.

  • Registered Users Posts: 3,096 ✭✭✭Ginger83

    Is there a minimum size the cable should be?

    The house was fully rewired in 2011/2012 and the shed built around then also.

  • Moderators, Home & Garden Moderators Posts: 4,486 Mod ✭✭✭✭graememk

    All depends on load, an indication of cable size is what size is the breaker that goes out there, if it's 32 you may be good

  • Registered Users Posts: 3,096 ✭✭✭Ginger83

    I have located it but I'm not sure. The trip switch has a few numbers on it. If I have uploaded the photo correctly it's the second last one on the bottom row.

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,832 Mod ✭✭✭✭Jonathan

    That's a 20A MCB, so given the length is likely 2.5mm². You could probably fit a 3kW inverter on that cable, but I put any more on that.

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  • Registered Users Posts: 3,096 ✭✭✭Ginger83

  • Registered Users Posts: 2,228 ✭✭✭bullit_dodger

    It's not so much distance of the cable, but the current going over it. As the lads above have said, that's a 20Amp breaker. So to avoid it tripping, I'd probably stay under 18Amps. which is (18 x 230) ~ 4.1Kw watts. So your max inverter size really is a 4kw with the existing cable.

    You might get lucky though and the spark used a heavier cable than the 20A breaker alludes to, but that would be unlikely. Most electrians won't do that as heavier cables are more expensive. As in there's no need to spend money on a cable which doesn't have the load.

    But don't be discouraged, most sparks are used to this type of stuff and can come up with a solution when they see your place, or put the inverter in the attic of your house etc.

  • Registered Users Posts: 3,096 ✭✭✭Ginger83

    Thanks. If the cable is as you and others have said I take it that I'm aiming for a max 4kw system subject to discussing with the installer?

  • Registered Users Posts: 1,824 ✭✭✭Markus Antonius

    I'm hoping in my situation that if the cable is undersized for the solar system I'm planning on putting in (6.4KW), that the electrician will be able to use the current wire to pull through a thicker one without having to dig up anything.

  • Registered Users Posts: 3,096 ✭✭✭Ginger83

    Yes it would be great if that works. I am happy enough with a smaller system to start with, it will help us reduce the bill a little.

    What is your views on a battery? Some do, some don't