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Critical Load Wiring with CU

  • 16-05-2022 10:39pm
    Registered Users Posts: 3,398 ✭✭✭

    Hi All,

    Just wondering how people have wired up their critical load from the Hybrid/Battery.

    A lot of people just seem to have a plug coming out but I'd like to wire it into the CU if possible.

    My understanding is I'd need to update the CB of the main load coming into the house so it swaps from main load to backup?

    Any advice appreciated.

    // Gary


  • Registered Users Posts: 793 ✭✭✭reklamos

    I am not sure what the Irish regulation says about it. There is a reason why inverters are grid tied and have to meet Irish standard.

    Critical load is meant to be critical load only and not normal house load. The easiest option is to have dedicated sockets, lights that are always powered from inverter's backup port. This way you keep isolation between grid and battery. This can be easely done by running backup cable to your switch board and then by moving some RCBO from grid to backup power.

  • Registered Users Posts: 2,334 ✭✭✭SD_DRACULA

    Would running the backup cable to a mini CU beside the main one and powering the lights from it work with the stupid way they ran some of the lighting circuits in here, like my house, without the neutral wire?

    N wire is at the light but not at the switches that is.

  • Registered Users Posts: 3,398 ✭✭✭randombar

    Is there constant current from the back up even when there's no power in the battery?

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,169 Mod ✭✭✭✭Jonathan

    Nothing stupid about how they are wired. You just don't like it because it makes it more difficult for home automation 😉 Yes, no reason why it won't work.

    @randombar Your options are to get your EPS output wired in one of three ways;

    1) get a basic backup socket

    2) pick a number of low load circuits that are always wired into the EPS feed

    3) get a change over switch fitted and power the entire CU from it, disconnecting both the incoming grid, and the regular inverter feed (you can't feed the inverter its own EPS output).

    Either way you'll need to get a suitable MCB/RCBO to stop you from drawing more than the EPS output can provide. Option three is most flexible, but most expensive. It will allow you to run stuff like central heating etc. Turning on high load devices like electric shower/oven will cause MCB to trip and plunge entire house in darkness.

  • Registered Users Posts: 2,334 ✭✭✭SD_DRACULA

    100%. Just lazy electricians that wired the house and yes it makes it a pain to get smart light switches but there are no neutral ones you can get, just have to put a capacitor between L and N at the light and voila - still have no idea how it works though.

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  • Registered Users Posts: 3,398 ✭✭✭randombar

    Ya I think I'd go for option 3, I think I'd find it very hard to decide what's in the critical load and what's not. A good point re regular feed.

  • Moderators, Motoring & Transport Moderators Posts: 6,522 Mod ✭✭✭✭Irish Steve

    Lazy electricians are the ones that put no neutrals or earth wires into the switches, which makes for a nightmare if you want to put metal plate switches on the walls to match the sockets. even more frustrating is when they did the first fix and wrapped the wires round a 4" nail where the conduits were going, and then didn't unwrap the wires from the nail when the threading the wires to the final location, which makes it impossible to draw in a new wire by using the old one to fish it through.

    To go back to the original thoughts on backup connections, one possible option, not that cheap, would be to put a pair of interlocked contactors on to the incoming supply to the distribution board, and set things up so that if the main supply is out for whatever reason the entire board can be brought back on line from the backup supply by activating the alternate contactor. A lot will depend on how much backup current is available, and if you can rely on the rest of the residents not to try and activate something that would be too big a load if running on backup.

    It would be possible to set it up in such a way that the backup is automatically activated in the event of the main supply failing, though it would be prudent to have a few seconds delay between one failing and the other activating to ensure that there's no surge issues, it's all too easy to damage some devices if they haven't fully shut down before the power comes back on.

    Shore, if it was easy, everybody would be doin it.😁

  • Registered Users Posts: 3,969 ✭✭✭mp3guy

    You'll be wishing you did the 3rd option if you do anything else. Had mine that way for a year and a half and reaped the benefits of it many times (out in the sticks).

    Post edited by mp3guy on

  • Registered Users Posts: 3,398 ✭✭✭randombar

    Ya few power cuts out in the sticks all right.

  • Registered Users Posts: 3,398 ✭✭✭randombar

    Any recommendations for a changeover switch?

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  • Moderators, Motoring & Transport Moderators Posts: 6,522 Mod ✭✭✭✭Irish Steve

    Are you looking for a manual switch, or a pair of interlocked contactors that can be set to operate automatically?

    Shore, if it was easy, everybody would be doin it.😁

  • Registered Users Posts: 3,398 ✭✭✭randombar

    Manual switch would be easier to come by id say and would fit into the cu too at a guess