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Discuss A/C installation "outdoor to indoor" cable query in the Electrical Wiring, Theories and Regulations area at ElectrciansForums.co.uk.

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  1. Zdb
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    Zdb Regular EF Member

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    UK
    So I went to a job yesterday where the A/C engineers had upgraded an air conditoning system and fitted new units. I was there just to switch on the power and do the testing and certification on the electrical side of things.

    They used the existing supply cable from the old unit (6mm) and MCB (B32).

    The bit that confused me was that the cable going from the outdoor unit to the indoor unit was only 1/1.5mm.

    Surely this is too small for the 32a MCB or am I missing something?

    Please can someone advise as I don't usually get involved in A/C installations.

    Thanks.
     
  2. anthonybragg
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    anthonybragg Electrician's Arms

    Location:
    NORTHAMPTON
    Business Name:
    CHARLTEC ELECTRICAL LTD
    We have got this set up on a job we are on at the moment where a 6.0mm SWA goes to outdoor unit and they have run 1.0mm flex to indoor unit I assume that it is internally fused.
     
  3. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    the load of the internal unit is a fixed load within the ccc of the 1.5mm or whatever cable is used. therefore overload protection for this cable is not needed.just s/c protection, which is provided by the 32A.
     
  4. Pete999
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    Pete999 Trusted Advisor

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    All the cable fro condenser to evaporator does is run the fan in the evaorator and is internally protected.
     
  5. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    even if it isn't, it's OK.
     
  6. Pete999
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    Pete999 Trusted Advisor

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    Morning Tel
     
  7. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    ditto, pete.
     
  8. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
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    Wilko Electrics
    Hi - don't suppose you noted the AC model ?
    Just thinking it might be worth looking at manufacturers doco.
     
  9. Spoon
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    Spoon Trusted Advisor

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    Depending on cable type, if the cable is 1mm isn't that too small, according to table 52.3 of the regs?
     
  10. Wilko
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    Wilko Electrician's Arms

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    Berkshire
    Business Name:
    Wilko Electrics
    Yes, but perhaps relying on manufacturers spec as its flex (last section of that Table)
     
  11. Spoon
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    Spoon Trusted Advisor

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    True mate. The OP didn't specify what cable it was. That's why I put 'Depending on cable type'
     
  12. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    do you mean round or flat? ;)
     
  13. Spoon
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    Spoon Trusted Advisor

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    Not sure what the regs mean by 'flexible cable' as all cables are flexible...when you bend them enough....
     
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  14. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    At risk of being a goody two shoes here, but I'm concerned that 1mm may not survive a low Zs sc on C32 (?) without damage if it was already running hot. Perhaps apply adiabatic?
     
  15. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    It was SY multi flex
     
  16. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    For disconnection times quicker than the stated 0.1 seconds given in appendix 3 the let through energy from the manufacturer of the mcb would be needed.
    So K2 x S2 must be equal to or greater than the I2t let through energy of the mcb for fault protection and tho damage doesn’t occur to the cable.
    As an example from hager a type b and c I2t value for a 32 amp mcb is 29kA for a 6ka device.
    S0 1.5mm should be fine given 1.5x1.5 =2.25 x 115x115 = 29,756.25 so 1.5 mm is protected in this example.

    Edit substituting 29kA in the Adiabatic equation gives a size of 1.48mm for compliance so 1.5 scrapes in.
     
    Last edited: Oct 13, 2017
  17. PEG
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    PEG Trusted Advisor

    Location:
    Manchester
    As pete said,most of these are fed from an internal board,which has its own protection,applicable to the csa of the cable used. As does the 120W circulatory pump,on a 8kW electric boiler.
     
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  18. Strima
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    Strima Electrician's Arms

    Location:
    St Neots
    Used outside?
     
  19. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    Yep used outside. It seems to be the cable of choice for these A/C engineers.
     
  20. Strima
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    Strima Electrician's Arms

    Location:
    St Neots
    SY is not suitable for use outside as it has very poor UV resistance and is not water resistant.

    After a few years the outer sheath cracks and the steel braid starts to rot.
     
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  21. Zdb
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    Zdb Regular EF Member

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    UK
    Agreed, however I see it being used all the time on A/C installs for the interconnection between the outdoor/indoor unit.

    I'm guessing the cable needs mechanical protection because it passes through a wall and they don't want to use an RCD for obvious reasons. Also you can't really use SWA as going by what I saw yesterday there's nowhere to terminate a gland.

    Both the indoor and outdoor units had a cable grip so nowhere to put compression / SWA glands.
     
  22. Zdb
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    Zdb Regular EF Member

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    UK
    Also from what I saw they don't even attempt to earth the braiding they just cut it off.


    Anyone come across this when looking at A/C installs?
     
  23. Strima
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    Strima Electrician's Arms

    Location:
    St Neots
    Do they need mechanical protection? Most A/C units I've seen are close to the wall so very little risk of impact damage.

    Also the braid should be earthed at the supply end.

    I'd be leaning towards using H07 cable for this type of application.
     
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  24. Pete999
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    Pete999 Trusted Advisor

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    I think what people need to realise is HVAC Mechs are a trade in their own right, and rightly so, whilst they are aware of the dangers of refrigeration gases, and the correct handling of a dangerous item, they tend to stick to their trade, and go with the flow regarding the electrical side of their industry.
    Until the manufacturers of split A/C systems, align themselves withe vagaries of BS 7671 we will always get these anomalies, as to what is the correct type of wiring needed to interlink the inner and outer parts of the system, remember most of the "Split systems" come with the interlink cabling included in the package, so with some experience in this area I would suggest that the IET and A/C manufacturers get together and iron out the correct way to install these systems, until they do we will always have this problem, blime a long post there Pete, take another sip.
     
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  25. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    Only use of earthing the braid is for it to act as screening as far as I’m concerned as it’s no good for taking fault current and is unsuitable to be used as a cpc in its own right.
    It offers very little mechanical protection to the cable.
     
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  26. multimick
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    multimick Regular EF Member

    Location:
    ormskirk
    Business Name:
    lathom electrical
    seen a couple of hot tubs recently which specified sy cable from commando plug to hot tub
     
  27. Leesparkykent
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    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    Never seen AC units where the indoor cassette is powered from the condenser. Usually just a control cable for signalling with the cassette on a fused spur and condenser on its own supply.
     
  28. Pete999
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    Pete999 Trusted Advisor

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    Just another way of doing it Lee, problem being AC/HV blokes don't always look at it that way, try and keep it all under one roof, so to speak, but yes seen it that way many times.
     
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  29. Leesparkykent
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    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    Yes mate we have recently started taking on the mechanical side of things so it's all under one roof.
     
  30. Pete999
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    Pete999 Trusted Advisor

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    Got your Gas safe handling qualification then?
     
  31. Leesparkykent
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    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    No I'm doing my gas safe ATM but we Have gas safe plumber and F-gas aircon guy cards in.
     
  32. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    I did my F-gas but steer clear of A/C work tbh. Best to stick to your own trade.

    So out of interest what type of cable do people recommend for this interconnection? Would need to be a multicore flex suitable for outdoor use.
     
  33. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    NYY-J / H07RN-F?
     
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