Distances questions .....

Good afternoon,

I am going to have the inverter and batteries in my garage.  It currently looks like an AJ array of panels, a Solis inverter and some Pylontech either US300 or US500 batteries.  The issue is that I have my consumer unit in one half of my double garage and I would prefer to have the batteries some 25 feet away in the other half of the garage.  It is a shorter garage and already has an oil boiler in it and my own car is fairly long and resides in the half of the garage that has the meter and consumer unit.

Are there any tough issues for us to have this distance between inverter (if it has to be by the grid entry isolating switch) and the batteries being that distant please?


  • QrizB
    QrizB Posts: 13,822 Forumite
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    edited 24 September 2022 at 4:56PM
    You need to keep your batteries close to your inverter.
    Why does your inverter need to be adjacent to your consumer unit? Mines in the loft while my consumer unit is under the stairs, so two floors away.
    Edit to add: is it because the wiring regs need there to be an isolation switch adjacent to the inverter, and one adjacent to the consumer unit? That's usually handled by fitting two isolators, one in each location. Is your installer trying to save the £30 cost of a switch by making you buy 50 feet of 60A DC cable instead? That seems a poor choice.
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  • ABrass
    ABrass Posts: 1,002 Forumite
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    The distance between inverter to consumer unit can be large as it's high voltage. The connection between inverter and battery is low voltage so a long run of cable has much higher losses.

    My battery is 30cm from my inverter, my inverter is about 10m from my CU.
    8kW (4kW WNW, 4kW SSE) 6kW inverter. 6.5kWh battery.
  • uk1
    uk1 Posts: 1,839 Forumite
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    Thanks both.  Fundamental misunderstanding of my options on my part and what you've told me is good news. 
  • To echo the above, my batteries are close to the inverter.. the Pylontech cabling is short but the connection to my consumer unit is wired from my garage up into the loft and down the other side of my house
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  • Heedtheadvice
    Heedtheadvice Posts: 2,459 Forumite
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    edited 25 September 2022 at 10:24PM
    To add a bit of engineering to those good responses regarding distances.
    There is no need to have an inverter close to the consumer unit but it is often convenient to have the electrics together for visibility of equipment and also to kerp the inverter in a lower ambient temperature compared to a loft as an example (general reliability benefits). There may be overvoltage issues if the distance involves a higher resistance path requiring a higher inverter voltage to overcome it and resulting in an overvoltage shutdown. Suitably sized cable usually overcomes any problem as the voltage difference is then small for a 16 or 20Amp current for an approx 4 or 5kW generator.

    Inverter to battery connections also will suffer a voltage drop both on charge and discharge. In this case being low voltage (and sensitive to value change) it requires much higher current values and is more susceptible to higher resistances in cables/connectors etc. The cables are usually rated for non enclosed operation and longer cables might have (but not necessarily) poorer cooling in trunking walls etc. causing a slight resistance increase. It all comes down to ohms law i.e. V=I x R when the current I is higher, for the same voltage loss the Resistance R needs to be correspondingly lower by ratio. So a typical 70 or 80 Amp charge/discharge an a smaller voltage variation together means very low resistance and hence bigger cable.

    Slightly bigger mains cable is quite cheap. Bigger DC battery cables are more expensive length for length and that adds up for much bigger long cables!
    (16mm2 cable say £5 per metre, 75mm2 at £25 per metre and then terminations might not fit too)
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