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Thread: Solar system and Eskom supply, (a Neutral Question)

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    Solar system and Eskom supply, (a Neutral Question)

    I am busy installing a Solar system(battries/inverter) which will supply just my lights and my plugs will still be good old Eskom.
    The problem I face is the neutral, should the neutral on the solar system be on its own or can the neutral be the same neutral bar as Supply N/bar. My gut feel is should be a separate and switched when reverting back to Eskom power.
    Can anyone can shed some light on this grey area I have.

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    Site Caretaker Dave A's Avatar
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    I'd suggest read this thread on connecting generators to an existing installation. The principles should be the same.

    Essentially, the installation under alternative power should be seperated from the installation under mains power (which means a seperate neutral bar).
    The trouble with opportunity is it normally comes dressed up as work.

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    Thanks for confirming my gut feel. I did read your posting on generators. I have
    sent my control circuit for review and was told that one contactor can not
    do the switching as the arc between N/O and N/C, will trip the board.

    Back to the drawing Board.

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    Diamond Member AndyD's Avatar
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    Yep you should switch the live and neutral so the Eskom supply and your inverter output never meet.

    I've installed a few solar /inverter systems for lighting and it's often easier to add a small enclosure with an extra MCB or two next to your changeover switch.


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    AndyD - That's what I wanted to achieve with the use of a contactor 2 x NO and 2 x NC but was advised that the arc would
    cause a major problem and that the reviewer had personal experience with such a circuit. I want to automate/remote the switching
    from Eskom to green and back to Eskom. I want to move my lights off Eskom by end of July. I am also buildind a vertical wind gen.
    So far the test have been encouraging.

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    Diamond Member AndyD's Avatar
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    I would use two contactors rather than a single one and add a small delay like 0.5 secs or even a mechanical interlock that physically prevents one of the contactors operating whilst the other is still energised. I agree a single contactor with 4-poles might be a problem with arcing plus a contactor with that 2 x NO and 2 x NC arrangement isn't a common item so it would probably be costly.

    A mechanical interlock with aux contacts is shown on this page.
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    Thanks, that what I'll have to do is user a delay between switching. The problem I want to overcome is that when the inverter
    switches off due to low battery voltage, Eskom must automatically be restored. I'll have a look at the page you sent me and
    do some "kop krap" and re-work my switching.

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    What you basically need is a standard automatic transfer switch. The difference is normally it would switch in an alternative power source if the Eskom supply failed, you need to configure it to work the opposite way around and give priority to the alternative source and use Eskom as a back-up so to speak.

    There are inverter units with all the controls built in such as these.
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    Diamond Member Justloadit's Avatar
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    If you have computers connected to this line, then I suggest you get a mini UPS on each computer, so that during the switching period, the UPS ensures your PCs are running of stable supplies.
    On some occasions during the switch over, depending if you have inductive loads or not, and CFLs are considered as an inductive load, and where the supply peaks are on ESKOM and your alternative supply are on opposite ends, The change over could create a surge in the load line which may hang up your PC and you may lose any unsaved information.
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    Solar and LED lighting solutions - www.microsolve.co.za

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    AndyD – thanks again, I’m going to use the changeover switch to start off with and the
    then setup semi auto, switching system. This project has taken a year to get this far.

    Justloadit, thanks for the advice, but my green power will be powering my light only.
    Last edited by Tinman; 19-Jun-12 at 08:06 PM.

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