Circuit for Aircon

[Morakot]

For a renovation project, I partly rebuilt upstairs of a house and intend to add and replace some air-con units.

 

However, the current electrical circuits upstairs appear nonsensical in places:

 

5 A -- Upstairs light, upstairs sockets, one air-con

30 A -- 9 KW water heater

30 A -- One air-con

30 A -- One air-con

30 A -- Empty

 

The above amp values are according the breakers in CU. I inspected some of the cables for these 30A circuits and they are thick multi-strand copper wires that look sound at a first glance.

 

1. What is a reasonable value for a separate light circuit (four bedrooms, one lounge, one bath room)?

2. What is a reasonable value for a separate socket circuit upstairs (two TVs, electronics, sound system, bed site sockets, iron, hair dryers, fans, etc)?

3. Is it possible to have two small air-con units on one circuit? The bedroom are relatively small between 15 - 25 Sq metres.

 

[Crossy]

There does seem to be a lot on that poor little 5A breaker.

1. If you are using CFL or LED lighting 5A-10A would be fine for the lighting (we have two 6A circuits).
2. Outlet circuit 16A or 20A (verify the cable size, if it's 1.5mm² then don't go above 16A if installing new then go for 2.5mm²).
3. Nothing to stop you putting two aircons on one breaker provided they don't exceed the rating of the wiring.

 

[Morakot]

Thanks @Crossy ! Very helpful.

[Morakot]

Must have been inebriated when I posted the amp value of the breakers... ????‍♂️ The breakers are actually 20A  for the first and 32A for the larger ones.

 

So what's the correct wire size for a 32A circuit?  Is it 6 sq mm?

 

 

 

 

 

 

[Crossy]

9 hours ago, Morakot said:

So what's the correct wire size for a 32A circuit?  Is it 6 sq mm?

 

Unless it's got a constant load of 30A or is in a very hot area 4mm² is fine on a 32A breaker. 

 

I would move to 6mm² if the load is constant or if you intend going to a BIG water heater (our 8kW heater is happy on 4mm²).

 

 

[Morakot]

4 hours ago, Crossy said:

 

Unless it's got a constant load of 30A or is in a very hot area 4mm² is fine on a 32A breaker. 

 

I would move to 6mm² if the load is constant or if you intend going to a BIG water heater (our 8kW heater is happy on 4mm²).

 

 

 

OK, thanks. No major constant load at all; air-con is only used intermittently, rarely more than one at the time. The wiring for this floor is in the roof space which can get a bit hot (less 45 C midday) though. I'm planning to have the cable in these yellow conduits.

 

I double check the situation with the water heater.

 

[bankruatsteve]

18 minutes ago, Morakot said:

 

OK, thanks. No major constant load at all; air-con is only used intermittently, rarely more than one at the time. The wiring for this floor is in the roof space which can get a bit hot (less 45 C midday) though. I'm planning to have the cable in these yellow conduits.

 

I double check the situation with the water heater.

 

FYI:  You don't need 30a breaker/wire for most AC.  A 20a breaker with 2.5mm² cable is plenty - even for two small AC on the same circuit.  In conduit, running single wires is preferred.

Edited October 7, 2019 by bankruatsteve

[Morakot]

4 hours ago, bankruatsteve said:

In conduit, running single wires is preferred.

Thanks, that's great!

[h90]

Something to check: Is there a earth wire and is it OK (just because there is a green wire doesn't mean it is OK).
Are the circuits really separate or are they somewhere connected....when it is old and many people have "repaired" things weird things can happen.
How the wires are connected to each other? Twisted together can be OK, so people told me (I hate it), but a 2.5mm2 wire doesn't help if a part between is 0.75 or badly twisted or corroded. Or worse twisted with tape around it and the tape fall off already.
I have seen things where you don't ask why did it fail...you ask why did it ever work before (like earth and zero exchanged...all the devices running on life wire to earth).

 

[Crossy]

14 hours ago, h90 said:

... like earth and zero exchanged...all the devices running on life wire to earth.

 

Our old condo was like that, all the A/C wired neutral to the ground bar. Supply had a good earth (TNS I think) so it all worked just fine until I wanted to install an RCBO.