20A IP65 isolator or 13A FCU first?

Discussion in 'Electricians' Talk' started by Jimbo, Jan 23, 2009.

  1. Jimbo

    Jimbo Active Member

    Afternoon all

    Got an air-con system run from a seperate 16A circuit directly from the CU with 20A IP65 rotary isolator next to the outdoor unit.

    Am adding a 13A FCU/timer indoors to control it, so question is whether to put this before or after the 20A isolator?

    NB indoor and outdoor interconnects are DC 24V only so so intermediatory switch gear.

    Many thanks
  2. JP.

    JP. Screwfix Select

    Myself would fit the FCU after the Rotary Iso Jimbo.

    Reason..total isolation of complete system which obviously includes timer (which presumably has a battery back up and non volatile memory)

    Must stress only an opinion from a non-sparks.
  3. Jimbo

    Jimbo Active Member

    Yes it has the usual internal self-destruct battery.

    That is my gut feeling about it as well.

  4. JP.

    JP. Screwfix Select

    I don't know what fuse you are going to use in the FCU but maybe it will be a 3 Amp one..

    I've forgot all the discrimination stuff..but presume it will discriminate with the 16 Amp MCB ok..maybe not important anyway.
  5. JP.

    JP. Screwfix Select

    Sinewave would be the guy to give an exact answer Jimbo.
  6. Jimbo

    Jimbo Active Member

    13A fuse, the unit itself is draws ~5A peak, timer in question supports 6A inductive so I'm assuming will run it OK.
  7. Jimbo

    Jimbo Active Member

    hopefully he'll be along later! Thanks
  8. bluevelvet

    bluevelvet New Member

    as said fit the fcu after the isolator that way you know when isolated the circuit is dead would expect the isolator next to the unit to be the first thing to go to
    when required to work on the unit or such,but would also adopt safe isolation procedures just in case
  9. fooman

    fooman New Member

    the indoor unit gets its power from the outside unit via the FCU :)
  10. fooman

    fooman New Member

    mains into the outdoor unit via your rotary isolator. Then another cable from the outdoor unit to your fcu and then to the indoor unit ;)
  11. sinewave

    sinewave Screwfix Select

    Hey up Jimbo!

    Why can't you use the inbuilt timer function on the A/C unit?

    Anyway assuming you can't then you'll need to wire as follows.

    16A radial to FCU/Timer

    FCU to external rotary isolator

    4 core feed & control flex/SY/YY cable back in to indoor unit.

    Trouble is you've already got the feed to the outdoor unit so may be easier to go from External to internal then back out again.

    Tother downside with just chopping the power to control operation is that if you have a electricaly operated condenssated pump then it won't operate after the power is chopped and this could lead to over flowing of the internal Air handlers drain pan! :O

    (Going Pub in 20 mins but will be back around 8pm for me T!)
  12. Jimbo

    Jimbo Active Member

    Thanks all!

    The inside unit has no mains feed, only a 24V DC link from the outdoor unit. As it happens changing the wiring whichever way is no problem :)

    Sine - the unit is a cheapo Hitachi Summit, only has a wireless remote and that only supports on..off timer, once off it won't turn it back on (pants, I know).

    It's primary heat source for an outbuilding so I want to run it 0630-0730hrs (E7 warm up), then 1000-1600hrs all at lowest set point so it doesn't get damp and is always comfortable when used.


    - Leave the feed to the Rotary Iso
    - Run back to the timer (next to the indoor unit)
    - Timer output to outside unit.

  13. Jimbo

    Jimbo Active Member

    Also no drain pump on this one :)
  14. Jimbo

    Jimbo Active Member

    Doh! Just re-read your post sine, should be then

    - Reroute 16A feed to timer
    - Timer out to existing 20A Iso.

    Sorted :)
  15. JP.

    JP. Screwfix Select

    Blowed if I understand it..seems all **** about face to me.
  16. sinewave

    sinewave Screwfix Select

    Don't worry about it JP, it makes more sense if you can see it! ;)

    My Head hurts! :(

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