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Topic Title: Most practical way to achieve simple supply overload interlocks.
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Created On: 15 July 2017 02:40 PM
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 15 July 2017 02:40 PM
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justinneedham

Posts: 85
Joined: 21 January 2005

Product suggestions please to set me off towards a painless way to achieve electrical interlock to prevent supply overload. I'll explain more.

Domestic house, standard 100A single phase supply. House is all electric (or that's the plan).
Difficulty is load sharing. Very fortunately no electric showers, but we have EV charger (32A), swimming pool heat pump, (21A) electric cooker, (not induction - at least not yet!..) normal sockets. Currently oil boiler.
Diversity, being a little inventive (ie realistic) brings this now nudging towards the 100A figure if cooker is doing it's normal stuff, kitchen/washers in use, EV charging and pool pumping...

The owner is planning a house heating heat pump. Now this is a not especially efficient 4 bed place. I think typical consumption in winter would rarely exceed 15A continuous, but installers are sizing up for a proposed a 14KW (input) model which at it's peak to a cold-start house could eat at least 50A .

I have explained my uncomfortable position re diversity. Owner is quite tech-savvy and understands. I'm less happy with the owner's proviso that "We won't run them all at the same time".

So I'd like an easy to implement interlock(s) (would probably need to be radio-based), to prevent at least perhaps pool heat pump and/or EV charger from operating at the same time as household heat pump.

From a practical perspective the pool heat pump operates off a 25mm SWA sub-main on an 80A supply end switchfuse, (yes it is 25mm, pool previously was "raw" 18 KW heater). Cable runs via the garage, and that supply eventually to be shared supply with the proposed household heat-pump (which would be outside the garage wall).
Some sort of (maybe radio-based) switching of contactors might potentially be the way to go. It's simplest using an either/or logic based on what's taking any current at all, or (more complex) a clamp on the main supply and some sort of algorithm which could disable one or other load till a lower threshold is reached.

TBD whether to involve the EV charger (on it's own CU off main tails Henleys now) in this sort of arrangement. This sort of backup must be quite common in industrial installs? I work domestic, so take it easy on me here.

I'd be unhappy about this sort of thing regularly chopping supply unexpectedly to active heat-pumps. I suspect that's not a good idea for many reasons. This would really be a backstop in case "user common sense" breaks down.

Best ideas, (including "ignore it" if that's your learned opinion..) let me know.
Rgds

 15 July 2017 06:04 PM
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kellyselectric

Posts: 104
Joined: 22 July 2016

I think you mite seriously want to consider having the heat pump and the EV charger on a separate phase_along with say the upstairs lights that will spread the load out a bit what you think?
 15 July 2017 06:54 PM
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justinneedham

Posts: 85
Joined: 21 January 2005

I did suggest that as one way out. It's an ultra-long driveway. I have not even begun to think of the potential cost to the Customer. I do perhaps need to put in an application to find out though.
 15 July 2017 09:23 PM
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Fm

Posts: 1658
Joined: 24 August 2011

Maybe write a SoP for the owner!
What about solar thermal tubes to lighten the current consumption on the pool heater.
Advise that money well spent on insulation is worth the investment, insulate insulate insulate before buying toys like heat pumps
 17 July 2017 11:44 AM
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AJJewsbury

Posts: 15533
Joined: 13 August 2003

 17 July 2017 01:29 PM
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weirdbeard

Posts: 3043
Joined: 26 September 2011

Is it on E7? What's the average units per day according to the recent bills? The new heat pump system specifies should be able to say how long 50A is likely to be drawn for?

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 17 July 2017 01:48 PM
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weirdbeard

Posts: 3043
Joined: 26 September 2011

How about a double pole 100A MCB in an REC2 type enclosure after the double pole 100A REC2 isolator, which would be easier for the user to reset, rather than having to book in a DNO engineer to replace the main fuse?

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:beer)
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