Electrical Question

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Piff

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Im looking at having air conditioning installed in my kitchen/dining/living room after the recent long hot period.
I’m being offered a choice of 2 systems, either 7kw or 10kw. The 10kw system would suit the room size better, but the 7kw would be better than nothing.
To install, I have easy access to a power socket on the kitchen ring main. Or, reasonably easily, I can take a spur off the garage ring main. The garage ring also serves the bedroom above and has a 32A trip. The kitchen ring also serves the utility room, hall & study and also has a 32A trip. Obviously the garage ring is more lightly loaded than the kitchen one.
The 10kw air con unit has a max running current of 21A. The 7kw unit has a max running current of 17A.
The main distribution unit is in the middle of the house and the only way I can see getting a dedicated supply for either of the air con units would be to run surface mounted mini trunking round part of the hall & through the utility room (this may be necessary one day in the future if we need a charging point for an electric car, though this isn’t a current consideration).

So the question is, can either of the air con units be run off the existing ring mains?
 
Almost certain that at those power ratings UK wiring regulations will demand a dedicated spur from your central supply.
 
Im looking at having air conditioning installed in my kitchen/dining/living room after the recent long hot period.
I’m being offered a choice of 2 systems, either 7kw or 10kw. The 10kw system would suit the room size better, but the 7kw would be better than nothing.
To install, I have easy access to a power socket on the kitchen ring main. Or, reasonably easily, I can take a spur off the garage ring main. The garage ring also serves the bedroom above and has a 32A trip. The kitchen ring also serves the utility room, hall & study and also has a 32A trip. Obviously the garage ring is more lightly loaded than the kitchen one.
The 10kw air con unit has a max running current of 21A. The 7kw unit has a max running current of 17A.
The main distribution unit is in the middle of the house and the only way I can see getting a dedicated supply for either of the air con units would be to run surface mounted mini trunking round part of the hall & through the utility room (this may be necessary one day in the future if we need a charging point for an electric car, though this isn’t a current consideration).

So the question is, can either of the air con units be run off the existing ring mains?

NO. Needs a dedicated supply, and isolator, using much larger cable size than a ring main. (you could use a cooker point if you have one in the kitchen)
 
Interesting.
The installer I will be using has just fitted 2 systems on a site where I’m currently working. There are 2 systems, 1 smaller wall mounted internal unit and a much larger ceiling cassette. Based in the size of the rooms I would guess that the smaller one is around 5kw and the larger is probably 10kw to 12kw. It’s not finished yet but the installer was there last week. As 2nd fix electrics are not done yet, he fitted 3pin plugs & used an extension lead off a 13A socket to commission them.
The final connections will be to external waterproof rotary isolation switches. But, electrician has installed 2.5mm twin & earth to each switch position from the distribution board.
 
NO. Needs a dedicated supply, and isolator, using much larger cable size than a ring main. (you could use a cooker point if you have one in the kitchen)
Cooker points in kitchen are nearby, but are in use. There are 2, 1 serving oven and the other serving combi microwave. They have 20A trips and if I remember correctly they each had 2.5mm twin & earth cable. Hob is separate on a 6.0mm twin & earth with a 40A trip.
 
Cooker points in kitchen are nearby, but are in use. There are 2, 1 serving oven and the other serving combi microwave. They have 20A trips and if I remember correctly they each had 2.5mm twin & earth cable. Hob is separate on a 6.0mm twin & earth with a 40A trip.

3kw (12amp) in theory should be roughly the max that should be used on a ring main socket, as other devices on the circuit will be adding to the load. 2.5mm cable can take up to about 22amps. So even the 7kw unit would be 28 amps. The hob supply would be my choice, but could in theory still be overloaded if all rings and a/c unit used at the same time. Although a calculation is allowed where cable size is calculated on a non maximum format.
 
3kw (12amp) in theory should be roughly the max that should be used on a ring main socket, as other devices on the circuit will be adding to the load. 2.5mm cable can take up to about 22amps. So even the 7kw unit would be 28 amps. The hob supply would be my choice, but could in theory still be overloaded if all rings and a/c unit used at the same time. Although a calculation is allowed where cable size is calculated on a non maximum format.

Hob circuit isn’t an option as it is in an island unit in the middle of the room.
Looks like a new feed from the distribution board. What size cable & what size trip would you suggest?
 
So, pulled the trigger on the 10kw unit. Supplier thinks that the 7kw unit would run ok off existing garage ring.
But as going for the 10kw one I’ll get a dedicated supply installed with 6mm twin & earth. Only thing I’m not sure about is what size mcb to ask for.
 
So, pulled the trigger on the 10kw unit. Supplier thinks that the 7kw unit would run ok off existing garage ring.
But as going for the 10kw one I’ll get a dedicated supply installed with 6mm twin & earth. Only thing I’m not sure about is what size mcb to ask for.

The 10kw air con unit has a max running current of 21A. The 7kw unit has a max running current of 17A

Don't know where those figures come from 10kw is 40amp. 7kw is 28amp. So I still think your on a dodgy track using a ring main circuit, even for the smaller unit. Consulting a professional would be my advice.
 
The 10kw air con unit has a max running current of 21A. The 7kw unit has a max running current of 17A

Don't know where those figures come from 10kw is 40amp. 7kw is 28amp. So I still think your on a dodgy track using a ring main circuit, even for the smaller unit. Consulting a professional would be my advice.

Those figures come from manufacturers literature
7kw
10kw
Is it the heatpump technology that is getting higher output from lower input?
 
Those figures come from manufacturers literature
7kw
10kw
Is it the heatpump technology that is getting higher output from lower input?

If the manufacturer is quoting those figures as maximum power consumption then, as above you will be drawing 40 plus Amps for the 10Kw unit at some point if we work on the basis that Watts divided by Voltage equals Current in Amps.

You quote "running current" which is the current or load imposed in a running state, there may well be a significantly higher in-rush current on start-up.

"For many years, mainland Western Europe has used a mains electricity supply rated at nominally 220VAC 50Hz. The UK used 240VAC 50Hz.

Currently, ALL Western European supplies are classified 230VAC. In reality there is no 230VAC supply unless you create one locally. 230VAC was a “standard” created during European "harmonisation" to give a single voltage standard across Western Europe, including UK and Irish Republic.

Although the ideal would have been to have a single voltage there were too many political, financial and technical obstacles to reduce UK voltage to European levels or to increase European voltage to UK levels, so a new standard was created to cover both. This was achieved by changing the tolerances of previously existing supply standards. UK voltage to 240VAC + 6% and - 10% and European to 220VAC +10% and -6% (thereby creating a manageable overlap) and we would call these two combined 230VAC, despite the fact that nobody was intentionally generating at 230VAC!

Depending on the voltage sensitivity of the product and the variance from nominal of the actual supplied voltage, it may not be advisable to use a 220VAC specific device in the UK or a 240VAC specific device in Mainland Europe etc. For instance a 240VAC supply can rise to as high as 254.4VAC and still be within tolerance, but the maximum rated voltage for a 220VAC product is only 242VAC. A 220VAC supply can drop as low as 206.8 within tolerance but the minimum rated voltage for correct operation of a 240VAC product is 216VAC It may work perfectly well either way but it could be, technically, outside the specification of the equipment with obvious implications. A 230VAC product must be compatible with all voltages across this range"
 
From the 10kw data sheet
Elecrical Data
Pdesignc kW 10
Pdesignh (@-10°C) kW 7.2
Annual electricity consumption (Cooling/Heating) kWh/a 531/2289
Power Source 1 Phase 220-240V, 50Hz, 220V, 60Hz
Inrush current (220/230/240v) A 14.4
Max. running current A 21
Power consumption (Cooling/Heating) kW 3.09 / 3.28

I think the 10kw is misleading. It is the max output, not the input.
If we use your sum W/V = A
W = A x V
W = 21 x 240
W = 5.04kw:dk:

The inrush current is stated as 14.4A
 
From the 10kw data sheet
Elecrical Data
Pdesignc kW 10
Pdesignh (@-10°C) kW 7.2
Annual electricity consumption (Cooling/Heating) kWh/a 531/2289
Power Source 1 Phase 220-240V, 50Hz, 220V, 60Hz
Inrush current (220/230/240v) A 14.4
Max. running current A 21
Power consumption (Cooling/Heating) kW 3.09 / 3.28

I think the 10kw is misleading. It is the max output, not the input.
If we use your sum W/V = A
W = A x V
W = 21 x 240
W = 5.04kw:dk:

The inrush current is stated as 14.4A
That is making a lot more sense!
I did think 10Kw cooling was a lot for a domestic environment.
 
Been out of the business for a long while, but most of those descriptions and figures are double Dutch to me. Pdesignh (@-10°C) kW 7.2 "Inrush current" WTF. don't tell me "made in China"
 
Kw - in air conditioning - is the output, not the electricity consumption. Confused? read on .......

MCB - it's not just the rating (in amps) that is important. An inductive load (like air-con) will be better suited to a "C" curve MCB, not a "B" curve.

It also depends on your existing installation - do you have a spare "way" on your consumer unit? Is the main isolator suitable for an inductive load - a RCD main incomer might prove troublesome.

At a guess - 6mm cable with a C32 MCB. But that's just a guess.
 
Kw - in air conditioning - is the output, not the electricity consumption. Confused? read on .......

MCB - it's not just the rating (in amps) that is important. An inductive load (like air-con) will be better suited to a "C" curve MCB, not a "B" curve.

It also depends on your existing installation - do you have a spare "way" on your consumer unit? Is the main isolator suitable for an inductive load - a RCD main incomer might prove troublesome.

At a guess - 6mm cable with a C32 MCB. But that's just a guess.
Pleanty of spare ways as have 2 split load consumer units. I was arriving at the same conclusion with 6mm cable and 32 MCB.
I'm not sure about the need for the need for a C curve MCB as we already have an air source heat pump and I believe that is on a B curve mcb, I'll double check.
 
Been out of the business for a long while, but most of those descriptions and figures are double Dutch to me. Pdesignh (@-10°C) kW 7.2 "Inrush current" WTF. don't tell me "made in China"
Not sure where they are made, but it is a Mitsubishi system, could save a few £s by going for a cheaper Chinese copy.......
 
IIRC, typical Coefficient of Performance (COP) for refridgeration/heat pump systems is between 3 and 4.

So for a 10kW cooling 'power', the compressor needs about 3kW of mechanical power which in turn might demand 3.5-4kW of electrical energy.

In my view, even though this could (just about) run off of the ring main, this sort of load should be on its own supply on a minimum of 4mm^2 cable, preferably 6mm^2, with its own 30A MCB. Even the 7kW is borderline.
 
IIRC, typical Coefficient of Performance (COP) for refridgeration/heat pump systems is between 3 and 4.

So for a 10kW cooling 'power', the compressor needs about 3kW of mechanical power which in turn might demand 3.5-4kW of electrical energy.

In my view, even though this could (just about) run off of the ring main, this sort of load should be on its own supply on a minimum of 4mm^2 cable, preferably 6mm^2, with its own 30A MCB. Even the 7kW is borderline.
I think this is the answer.
The installer is not an electrician but has run these systems off a ring main, most recently at the site where I have been working where he commissioned them off an extension lead pending the sparky fitting the correct isolation switches to the dedicated cables installed (which I think are 2.5mm twin & earth).
I now know enough to talk to the electrician and not have the wool pulled over my eyes.
 
Hi,
If he has been running off of a normal 13A Plug & Socket than it isn't drawing 13A, max fuse rating for a 13A plug is 13A.
Is the A/C made up of two separate pieces of kit? eg condenser assembly (normally external to the building) and the Evap unit (in this case the unit on the wall) as this might explain why he is able to run both the 7 & 10kw units off of a 13A socket.
If the data sheets are correct then for the Max current stated would be for both units, I would be looking at 4mm or 6mm cable with a 32A MCCB Type B (though you could more than likely get away with a standard type), almost certainly the Max current stated is for the starting currents of the inductive load within the unit(s)
What ever sizes you choose just make sure that the Current carrying capacity of the cable exceeds the rating of you're chosen MCCB.
 

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