Domestic Aircon power supply

[ericmark]

We have items which heat the house, which in winter is not a problem, but in summer is. So we have tried to reduce the heat output of equipment as much as possible, so our lights, TV, and many more items are today using switch mode power supplies and vastly reduce the power used in the home.

There are items which do draw more, like charging an electric car. But we are looking at the loading of circuits within the home, not the total that the home uses. My parents, my first, and second house, all had Wylex fuse boxes with 4 fuses. Cooker, Ring final, immersion heater, lights. Today my home has 14 RCBOs plus an UPS circuit still with a 60 amps incoming fuse, so 8 circuits feed 13 amp sockets, until now never counted them, but 2 feed outside sockets, 2 also feed cookers, 1 is the ups, remaining 3 ring finals.

We have no idea on how many circuits @DIYjobber intends to spread the load over. And with a ring final, how close the heat pump load would be to the centre of the ring. We are told the load is 1.56 kW which should not really be a problem. In summer, I use a portable AC, which I never even considered would need a dedicated supply for.

However, if I wanted a heat pump, I would include the cost to modify my installation in the cost when selecting the device. The same as any other household appliance, be it an oven, hob, shower, or heat pump, one has to include installation in the price, if to change my electric shower one model would require heavier cable to be drawn in, I would include that cost when selecting the shower.

 

[DIYjobber]

We have no idea on how many circuits @DIYjobber intends to spread the load over.

I have 4 x 32A ring mains in my home, but I would of course only use one of them. The A/C contractor I use will no doubt include the installation in the price. I see no compelling reason why an air conditioning unit which supplies 2 rooms and takes an electrical load of just 1.4kW cooling, or even 1.56kW heating, should not be wired in to one of the 32A ring mains via a fixed wired spur, and neither does the accredited installer I will probably use. My gas boiler is connected to one of the ring mains via a 13A plug, quite common practice when the house was built; The built-in fridge-freezer is plugged in; So is the built-in Neff microwave oven, and the integrated dishwasher, all "fixed" appliances, all fed from ring mains. Cabling back to the main consumer unit is not practicable. The only other alternative would be to combine 2 of the ring circuits into one ring circuit, and use one leg of the "redundant" ring to become a dedicated circuit for the air conditioning unit. Of course, that would put more sockets and their associated load onto one of the existing ring main circuits, while one of the the "redundant" 2.5mm leg would be downgraded to 16A and carry the 6 amps cooling load. The overall load in the house would be the same.

 

[morqthana]

The rotary isolator, is a grey, plastic cased unit, with a bright red knob, and a clear yellow on/off markings, beloved of AC engineers.

And the facility to be padlocked off.

 

[morqthana]

I am a former electrician, though not certificated any more. Nevertheless, I still do my own electrical work at home. I am considering air-conditioning and would like to install the power supply to the outside wall, for a single Mitsubishi MXZ-2F53VF condenser unit with 2 internal (cooling) units.

What type of RCD have you got?

 

[DIYjobber]

What type of RCD have you got?

30mA.

 

[davelx]

30mA.

That's not the type, it's the differential current trip rating. Post a photo of the front face of the RCD and we should be able to tell from the markings.

 

[morqthana]

See p20

BEAMA GUIDE TO THE SELECTION AND APPLICATION OF RESIDUAL CURRENT DEVICES (RCDs)

www.beama.org.uk

 

[morqthana]

They say it will need a separate 20 Amp supply, whereas I cannot see why I cannot feed it from my ring main, via a suitable isolating switch.

Given the probable RCD problem, a separate circuit might be easier.

 

[DIYjobber]

The RCD issue is a new one for me. It is a type A. It works okay with my 7kW car charger and all the other gismos in the house, but I hadn't realised there were different types for different applications. The (preferred) Mitsubishi A/C unit manual does not appear to specify the required type of RCD. I will act the dumb customer and let the A/C company install the thing - it's their job, they are accredited and have been installing them for 20 years so hopefully they know what they're doing. If they have to install a separate circuit with its own RCD, then so be it, but it's going to look pretty ugly, as they cannot get a new cable from the mains position without surface wiring on the outside of the house for part of the way.

 

[davelx]

Given that compact type A double pole bidirectional RCBOs are now readily available for the major CU brands at close to the same price as other types, I can see no reason to install anything else unless there is a specific requirement for a different type.

Or am I missing something?

 

[morqthana]

they cannot get a new cable from the mains position without surface wiring on the outside of the house for part of the way.

Have it all on the surface all of the way and it won't need an RCD of any sort

 

[securespark]

I could have 2 x 3kW appliances on a twin socket on a ring main if I wanted to.

It's not good practice.

A double socket loaded with 2 x 3 kW loads wouldn't last long.

Best to have a single for each.

 

[Harry Bloomfield]

It's not good practice.

A double socket loaded with 2 x 3 kW loads wouldn't last long.

Best to have a single for each.

I would be wary of even that, as a long term solution, if the 3Kw is a constant, uninterrupted 3Kw.

 

[securespark]

I didn't say they were uninterrupted.

How many domestic 13A loads are?

 

[Harry Bloomfield]

I didn't say they were uninterrupted.

How many domestic 13A loads are?

Most are not a constant draw of 3Kw, if you think about it. Fan heaters, washing machines, driers, all usually include a thermostat, and switch off frequently, allowing both socket, and plug to cool down.