Cable / Breaker sizing for Air Source Heat Pump

[bh00]

Hi,

I need to connect an air source heat pump outside. The rating plate lists the following info:
Voltage: 220V 1ph
Load: 2kW
Running Current: 9.5A
Breaker Size: 20A
Cable Dia: 4mm2

Now, knowing it was a 2kW unit, I cabled in 2.5mm SWA from the house to the install location (approx 15m) and put a 20A MCB protected by an RCD on the feed.

The unit's manual is stating 4mm2, but at 9.5A (and checking with various online resources on current vs wire size), 2.5mm or even 1.5mm would be suitable for this task, correct?

Please advise!

 

[davelx]

Hi,

I need to connect an air source heat pump outside. The rating plate lists the following info:
Voltage: 220V 1ph
Load: 2kW
Running Current: 9.5A
Breaker Size: 20A
Cable Dia: 4mm2

Now, knowing it was a 2kW unit, I cabled in 2.5mm SWA from the house to the install location (approx 15m) and put a 20A MCB protected by an RCD on the feed.

The unit's manual is stating 4mm2, but at 9.5A (and checking with various online resources on current vs wire size), 2.5mm or even 1.5mm would be suitable for this task, correct?

Please advise!

The running current is 9.5A but the start-up current will likely be greater - indeed it could be a lot more since MCBs can carry significantly more than their rated current for a short time without tripping. (Ask yourself why they specify a 20A MCB rather than a 16A?).

So you need to be concerned about the start-up current and the resulting voltage drop when the unit starts up - if it's too great then the unit may not start cleanly/reliably. This is probably why they specify 4mm² cable.

Of course, the actual VD will depend on the length of the cable run too - 15m in your case. I suggest a call to the manufacturer's technical support line.

 

[bh00]

Hi,

Thanks for the reply. This is what I assumed - that the inrush of the compressor starting was quite high. It doesn't specify a D-curve and is fitted with a soft-start circuit so I hoped it wouldn't be the case.

Many thanks

 

[EFLImpudence]

Just out of interest -

Do the MIs state 'Cable dia' or is that your typo?

 

[bh00]

It's listed as

Cable Diameter mm2: 4
Cable Diameter AWG: 12

I'm assuming they typoed and they actually mean 4mm2 sized cable, not diameter.

 

[EFLImpudence]

It's listed as
Cable Diameter mm2: 4
Cable Diameter AWG: 12
I'm assuming they typoed and they actually mean 4mm2 sized cable, not diameter.

Quite.

So, perhaps their other instructions are suspect as well.

As suggested, contact them and see if they know.

 

[ban-all-sheds]

I'm assuming they typoed and they actually mean 4mm2 sized cable, not diameter.

They must have done - the dimension of diameter is not mm². And a cable with conductors 4mm in diameter would have a csa of 12.6mm²

 

[winston1]

Why is it 220 volt? Is it a grey import from Europe?

 

[securespark]

2000W at 220V is just over 9A.

The next breaker size up is 10A. Could the manufacturers have played safe and doubled the breaker size to allow for start-up current surging over the 10A mark?

And then correspondingly upped the cable size to allow for voltage drop on runs outside?

I suppose it's anyone's guess...