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SINGLE PHASE LOAD SHEDDING

John Peckham

I design LV electrical installations including large current hungry domestic installs. I am frequently having single phase supplies upgraded to 3 phase for these houses due to mutiple ovens in kitchens, ASHP, AC units, EV charging etc loads. If I cannot get an upgraded 3 phase supply I want to use load shedding so that the single phase supply capacity is not exceeded. I am looking for a simple 3 phases device with current coils on the supply that will disconect chosen loads. I do not want any fancy electronics or PLCs etc. Can anyone recommend any product on the UK market that will do this.


Thanks

JP

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  • 0

    There are plenty of current monitoring/load shedding relays about - e.g. https://uk.rs-online.com/web/p/monitoring-relays/8577072?gb=s but it's can get quite "interesting" quite quickly once you move past the "when a high load high priority load is on, disconnect all the low priority loads" kind of logic. What seems simple - e.g. switch off large load when overall current > 80A (and therefore turn it back on when overall current is <80A) can easily get into an unstable oscillating state (you probably already thought of that, but just in case...)

    On the subject of load shedding heat pumps - like a lot of compressor driven stuff I suspect they won't appreciate just having its power removed unexpectedly - mine came with "ESCO" contacts (intended to respond to a DNO signal to shed load) and an option for separate peak (constant) & off-peak (timed) supplies ... either way, plan to run at least one extra cable - which might have to go to the outside unit or the indoor controller.

      - Andy.

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    What seems simple - e.g. switch off large load when overall current > 80A (and therefore turn it back on when overall current is <80A) can easily get into an unstable oscillating state (you probably already thought of that, but just in case...)

    That occurred to me too. I suppose that it could be addressed by having a relay/contactor which opens on loss of power and needs to be re-closed manually.

  • 0 in reply to Chris Pearson

    Manual reset probably isn't ideal from a consumer's point of view (flat EV in the morning because one of the teenagers had a late night shower and neglected to press a button afterwards?). Interestingly that Schneider unit seems to take a not dissimilar approach - but resets automatically after 5 or 10 mins (so if the overload remains it will keep reconnecting, overloading, then disconnecting ... which doesn't seem ideal). If you want to avoid a "smart" system (that can dynamically adjust according to the actual loads) I would have thought it would be simpler to measure the side you're *not* disconnecting - with a margin to allow for the disconnectable load. So say you had a 20A low priority load and a 80A supply, you'd disconnect when the priority loads exceeded 60A (i.e. the 20A margin no longer remains) and reconnect once it had dropped below (with a time delay if you wish). You could cascade such an arrangement for several low priority loads if you wished. E.g.

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  • 0 in reply to Chris Pearson

    Manual reset probably isn't ideal from a consumer's point of view (flat EV in the morning because one of the teenagers had a late night shower and neglected to press a button afterwards?). Interestingly that Schneider unit seems to take a not dissimilar approach - but resets automatically after 5 or 10 mins (so if the overload remains it will keep reconnecting, overloading, then disconnecting ... which doesn't seem ideal). If you want to avoid a "smart" system (that can dynamically adjust according to the actual loads) I would have thought it would be simpler to measure the side you're *not* disconnecting - with a margin to allow for the disconnectable load. So say you had a 20A low priority load and a 80A supply, you'd disconnect when the priority loads exceeded 60A (i.e. the 20A margin no longer remains) and reconnect once it had dropped below (with a time delay if you wish). You could cascade such an arrangement for several low priority loads if you wished. E.g.

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  • 0 in reply to AJJewsbury
    AJJewsbury said:
    (flat EV in the morning because one of the teenagers had a late night shower and neglected to press a button afterwards?)

    Teenager washing???

    So prioritise the EVCP. Anybody who wants a shower in the mean time will have to wait or have a cold one.

    (When I was a teenager, we had a 3 kW shower, which was a bit meagre, especially in winter.)

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