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  1. #1
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    1.5mm interconnect vs 1.0mm cable- make much difference?



    Have a Mitsuibishi SRK25ZJS (mini split inverter, 9000btu) and was sourced an interconnect although it's 1.0mm and recommended is 1.5mm in manual. HVAC guy said 1.0mm is fine to use and most of his customers use it in similar sized systems.

    Any insights into this?



  2. #2
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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    I would always follow the manufacturer's recommendation, skimping on the interconnecting cables is a recipe for communication errors...
    (Remember, the interconnecting cable not only carries the current but also the data communication)


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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    telephone cable carries far more data thousands of miles on much smaller cross section. the indoor unit draws less than 1 amp. I can only assume they are not very good at their job if they spec 1.5mm or build a very large fail factor like daikin recommending a 16a supply for a vrv fan coil

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    1.0mm it is then- if I catch on fire etc and you don't hear from me again, you'll know why.

    Cheers

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    The interconnecting cable is sized from fuse ratings, on smaller splits the link for power down terminal 1 is often directly off the mains connection which goes back to a 10,13,16 amp breaker.

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    the problem is occure when there is drop in voltage
    as example if the current draw from the air conditioner is 5 amp and voltage is 220
    1 mm cable will withstand it
    but if the voltage is dropped to 210 volt or less
    the current draw will rise to 6 or 7 amp
    here the 1 mm cable will not with stand the current and can lead to unit failure


    so the 1.5 mm cable will be ideal
    .
    always obey manufacturer instruction
    Last edited by kefah; 04-09-2013 at 10:33 PM.

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    Quote Originally Posted by kefah View Post
    the problem is occure when there is drop in voltage
    as example if the current draw from the air conditioner is 5 amp and voltage is 220
    1 mm cable will withstand it
    but if the voltage is dropped to 210 volt or less
    the current draw will rise to 6 or 7 amp
    here the 1 mm cable will not with stand the current and can lead to unit failure


    so the 1.5 mm cable will be ideal
    .
    always obey manufacturer instruction
    What if it drew 100a?

    a std split doesn't draw anything like 1 amp let alone 5a. So why mention 6 or 7a?????? plus 1.0mm is rated to 15a (before losses)
    http://www.eland.co.uk/documents/YY%...l%20Cables.pdf

    The comment about fuse rating is valid but again how many use 4mm interconnect on a 12.5kw split????

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    12,5kW split will have power supply at outdoor unit! Interconnect will be sufficient at 1.5mm2. Power supply to outdoor will need 4mm2.

    Smaller split units 2,2-3,5kW (cooling capacity) are usually supplied from indoor unit, and interconnect cannot be smaller than 1,5mm2 since inverter (or non inverter) amperage draw is limiting factor. In such case outdoor unit inverter (or compressor) is supplied from indoor unit (over relay) directly (without fuse) and interconnect diameter should be dimensioned for maximum power at outdoor unit.

    Pay attention to how unit is supplied and how wiring is fused internally, and you will know what can and what cannot be done. Nevertheless, always follow manufacturer instructions to be safe regarding warranty and legal matter in case of accident.

    If you use smaller diameter than fuse rating allows, than you should increase diameter or fuse separately to allowed amperage for that size.
    Last edited by nike123; 05-09-2013 at 07:29 AM.

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    Quote Originally Posted by nike123 View Post
    12,5kW split will have power supply at outdoor unit! Interconnect will be sufficient at 1.5mm2. Power supply to outdoor will need 4mm2.
    no as the above said the interconnect links directly onto the mains in. therefore it is a continuation of the 4mm mains supply. therefore it must be of the same size as it has the potential to carry the 32a. using a 1.5mm is as non compliant as using 1.0mm cable.

    Smaller split units 2,2-3,5kW (cooling capacity) are usually supplied from indoor unit, and interconnect cannot be smaller than 1,5mm2 since inverter (or non inverter) amperage draw is limiting factor. In such case outdoor unit inverter (or compressor) is supplied from indoor unit (over relay) directly (without fuse) and interconnect diameter should be dimensioned for maximum power at outdoor unit.
    not in the UK. most splits are outdoor unit supplied. There are only a small number (2 mhi fixed speed) units which are fed from the indoor unit. If that is the case you should use at least the same as the flex supplied or larger. I do not inc ebay

    Pay attention to how unit is supplied and how wiring is fused internally, and you will know what can and what cannot be done. Nevertheless, always follow manufacturer instructions to be safe regarding warranty and legal matter in case of accident.

    If you use smaller diameter than fuse rating allows, than you should increase diameter or fuse separately to allowed amperage for that size.
    cable is sized for fuse not manufacturers recommendation. they always state 'check your local regulations' which means you cannot sue them if it fails. Daikin always rated their small 3.5kw splits at 16a. they realised they were losing sales as it could not be fitted to a 13a fuse spur. their answer was to down rate to a 10a suddenly they could be fitted to a 13a spur. nothing changed apart from the installation manual
    Last edited by r.bartlett; 05-09-2013 at 10:33 AM.

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    I have been using 1.0mm (when the rower goes directly to the OD) cable on small split units for a decade and haven't had a single problem!... except mise...

    if the power suply is through the indoor unit, then yes i would definetely go with 1.5mm

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    Lots of chatter....do what the install manual says and when it goes wrong there's less to think of. If you don't follow the manufacturers guidance and get a phantom problem you'll be second guessing for hours....

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    Quote Originally Posted by r.bartlett View Post
    What if it drew 100a?

    a std split doesn't draw anything like 1 amp let alone 5a. So why mention 6 or 7a?????? plus 1.0mm is rated to 15a (before losses)
    http://www.eland.co.uk/documents/YY%...l%20Cables.pdf

    The comment about fuse rating is valid but again how many use 4mm interconnect on a 12.5kw split????
    at least following manf. instruction is best than ignore it

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    Re: 1.5mm interconnect vs 1.0mm cable- make much difference?

    Lets not confuse volt drop with transformer primary and secondary turns ratio, if there's volt drop it will be due to common factors such as copper loss, I squared x R losses, or peak demand conditions on phases causing the current to drop or increase proportionately with the voltage. And not increase as it would with a transformer situation.

    Also its not the conductor size alone that limits the amount of current, its other correction factors that sometimes need to be applied such as insulation type, contact with other materials, bunching, spacing, ambience, and length of run to name a few.

    I have seen 1.00mm pyro connected to 240 volt and draw 48 amp and the sheathing just start to glow red, but at its terminating end the voltage has only been 190 volt. Also I have seen 2.5 mm twin and earth draw 58 amp, and you could leave your finger prints on the sheathing it was that soft and hot.

    From experience I know that 1.00 mm will easy take 10 amp all day long in most conditions, but when the other conditions exist, then the conductor size will need to be increased. The NICEIC recommend that 1.5 mm is the smallest size conductor that can be used to be connected into a 13 amp spur, (fused connection unit). But that only applies in the UK.

    When a pvc/pvc twin and earth/romex (BS 6004) cable is surrounded by thermal insulation for only a meter, its current rating is reduced by half, unless you apply the correction factors which could still then result in the same reduction.

    Manufacturers will probably recommend certain conductor sizes to allow for such correction factors, so that any losses are kept to a minimum, and support any disclaimers should any loss arise. And they do occasionally state that wiring to be undertaken by electrically competent persons.
    Last edited by chilliwilly; 08-09-2013 at 09:27 AM. Reason: missing text
    Training may be finished but experience is never complete.

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