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5kw Air-conditioning unit wiring

Discussion in 'Electrics UK' started by Armz, 19 Jun 2021.

  1. Armz

    Armz

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    Hi all I am currently looking at having a 5kw air-conditioning unit installed in my house.

    I have had two quotes but both installers are telling me different things when it comes to wiring the unit.

    The first engineer is saying that he can wire the unit off my upstairs ring main with a 20amp fused spur which he says will be ok because I hardy use my ring main upstairs (only Charing phone and hair dryer) and it's on a 32amp breaker in my fuse box. Which I get what he's saying.

    The second engineer said I would need to get an electrician in to run a cable on its own breaker to the unit. Which I also get.

    I would naturally go for the first option as it would be less work and won't cost as much but I'm not 100% sure if this would be safe?

    I would appreciate some feedback thanks.

    AC unit spec
    5kw
    max rated current 14.5A
    20A fuse required
     
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  3. JohnW2

    JohnW2

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    Well, for a start, the largest fuse available for a standard 'fused spur' from a ring circuit, using a Fused Connection Unit (FCU) is 13A, so he would have to think of some non-standard way to provide the 20A fuse (or breaker) for a spur off the ring. This would be an unusual, and far from ideal, way of doing it.
    That would certainly be the usual and 'expected' way to do it.
    I'm not sure where that "14.5A" comes from. If the 5 kW is quoted for 230V, that would represent a current of about 21.7A. If the 5 kW relates to 240V, then that would correspond to almost exactly 20A (at 230V).

    Kind Regards, John
     
  4. Armz

    Armz

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    Hi John thanks for your response I have uploaded a picture of the unit specs if that helps in respect to the 14.5 amp
     

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  5. JohnW2

    JohnW2

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    Thanks. It doesn't really help. However, if its around 5 kW then I would assume something like 20A maximum (and forget the 14.5 A, whatever that may be), which is consistent with their calling for a 20A fuse.

    Kind Regards, John
     
  6. bernardgreen

    bernardgreen

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    Possibly 3.5kW of electrical load used to pump 5kW of heat into the house
     
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  7. ericmark

    ericmark

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    I have also noted that with heat pumps, the heat transferred is more that the power used. If inverter controlled a heat pump can have very little in rush and there is little problem with volt drop, but the older systems have a high in-rush and volt drop is a problem. I think the one quoted is inverter control?

    From the centre of the ring you could take that load, however there is no 20 amp FCU so it would be likely a mini consumer unit upload_2021-6-19_7-22-57.png as to if it needs a fuse or MCB not sure, some inverters need a semi-conductor fuse to protect them MCB's are too slow. But likely would be a MCB. As one leaves the centre of the ring the problem is overload of the ring circuit. So one would need to measure the loop impedance to see if near centre or ends of the ring.

    Using a cooker connection unit and a MCB in the main consumer unit would be neater. It also depends on if 20A is maximum size, or if a 32A could be used. People tend to read any overload protection must be included in the appliance, the fuse in plug only protects cable, but fail to realise that is only true with a portable appliance, with a fixed appliance the manufacturer can stipulate protection required, so it would need careful reading of the instructions.

    I have been caught out with AC's in the past, remember Next in Chester and being told the AC was something like 1 kW there were a lot of them, but this was only the head, the units on the roof were something like 7 kW each and I seem to remember about 8 or them, seem to remember pulling something like a 50mm² cable to the roof to power them, that is a beast of a cable.

    My AC here is too small really, but a simple portable unit and the exhaust goes up the flue so no open windows.
     
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  8. zebedee2001

    zebedee2001

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    By a 20A fused spur I wonde if he actually means a 20A switch/isolator.
     
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  9. winston1

    winston1

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    That is pretty inefficient for a heat pump. I’ve seen them where the electrical load is a third of the output, but that was for heating rather than cooling.
     
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  11. ericmark

    ericmark

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    Very true what @zebedee2001 says I am not sure I would want one of these [​IMG] on the wall.
     
  12. winston1

    winston1

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    A 20 amp load on the ring won’t overload it even near one end as ring cable is rated at more than 20 amps. But is is bad practice and I wouldn’t do it.
     
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  13. bernardgreen

    bernardgreen

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    The COP ( Coefficient Of Performance ) depends on the difference in temperature between the source ( air outside the building ) and load ( air or water inside the building ).

    Quoting from HERE

    Air-source heat pumps generally have COPs ranging from 2 to 4, implying that they deliver 2 to 4 times more energy than they consume. Water- and ground-source heat pumps normally have COPs of 3–5. The COP of an air-source heat pump decreases as the outside temperature drops. Therefore, two COP ratings are usually given for a system: one at 8.3°C (47°F) and the other at − 9.4°C (17°F). When comparing COPs, one must be sure the ratings are based on the same outside air temperature to avoid inconsistencies. COPs for ground- and water-source heat pumps do not vary as widely because ground and water temperatures are more constant than air temperatures.

    EDIT just realised the OP is talking about air conditioning ( one assumes ) to cool the house on a hot day. The calculations of COP are different.

    Heat pumps heating a building put the electrical energy + pumped heat into the house. The electrical energy contributes to the heating.

    Heat pumps cooling a building take pumped heat from the house, add it to the electrical energy and dump both outside. The electrical energy does NOT contribute to the cooling as it is dumped outside
     
    Last edited: 19 Jun 2021
  14. ericmark

    ericmark

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    Seem to remember it says some thing like
    the (ii) and (iii) is the bits we are looking at, but it does not say you must not feed items over 2 kW it simply says by not having any it will be unlikely to exceed for long periods the current-carrying capacity of the cable. The ring final uses 20 amp minimum cable, with a 32 amp MCB/RCBO, or 30 amp fuse, so over 32 amp it will fail safe, but near the ends if a 32 amp load is put on the cable it could be 30 amp in one leg and 2 amp in other leg, so the AC would not overload the cables, but other items used could tip it over the edge. So if the AC uses 8A on one leg and 6A on the other it is unlikely a 18 amp load would for a long period load one leg only. But if the split is 12A and 2A then it is more likely.

    To my mind the stumbling block is to get an electrician to issue a minor works saying he has done the work complying with BS7671, it may be technically permissible, but would you want to put your name on the minor works? Today with the landlord EICR we have the problem if the property is rented in the future some one at some point will be inspecting your work, and no one wants a claim that their work did not comply even if really it does, so think it unlikely an electrician would issue a minor works for a 20A fused isolator on a ring final.
     
  15. EFLImpudence

    EFLImpudence

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    The sticker pictured states 14.5A (and 20A fuse) - it does not state 5kW.
     
  16. flameport

    flameport

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  17. 333rocky333

    333rocky333

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    Is it not like a commercial unit where the isolater is usually a rotary one outside with the wall unit.
    i believe some internal units now just run from a cable from the outside unit not needing its own isolater inside the house
     
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