3phase aircon

[nick1986]

Hi guys I was wondering if you could help me I have an old aircon unit it's 3phase it's feed from a 3 phase 32 A trip. We are having the aircon changed to 5 single phase ones now my boss reckons that just put the old 3phase (at the A/C unit) in a jb and just tap of each phase and neutral for the single phase but can the neutral be shared? Also is the breaker ok as my boss says thats fine. I was going to run new cables to each with single 16A trips? I would be very greatfull on some answers. Cheers Nick

 

[steptoe]

we need loads more info on this,

size,

length of runs

cable size

etc etc etc

oh, and as AC units will most likely require C or D type I think you may well struggle with Zs too most likely,

ask your 'boss' for some more info.

 

[nick1986]

Thanks for the reply there is (1x 20A) (2x 7A) 2x 4A. *Aircon units*The run is only 10meters the cable is only 2.5mm. I was going to run single feeds to each unit with a 16A mcb. Thanks for your help.

 

[steptoe]

ok,

well 16A MCB wont run a 20A load !

why would the 7A and 4A AC units need a 16A MCB ?

what is your Ze, or Zdb ?

what is your current loading?

what type breakers do the AC units require? Cs or Ds ?

what you are currently proposing is to have a 42A load on a 2.5mm cable,

you need to do some cable calculations.

and then design a circuit to suit,

load<OCPD<cable

 

[nick1986]

Thanks for your help. Sorry I didn't mean 16A I don't know why I put that. I was at work and the boss walked in. They need a type c mcb.

 

[steptoe]

what is your Zdb?

remember that C type is half max Zs compared to B type.

then work out your design current, and volt drop for what ever size cable you are using,

you also need to take into account the submain to your local Db too.