SWA to Air Source Heat Pump

[Woslights]

I am having an Air Source Heat Pump fitted, it is rated at 8kw i have had 2 quotes from sparkies, 1 quoted for 6mm SWA & 1 quoted for 10mm SWA.

The cable run is from a new secondary CU on a 40A MCB, the cable runs in a void below the house (concreate floors & 3ft void to the ground) then a 2m trench to an isolator switch beside the unit (63 Amp TP&N Rotary Switch Insulated Weatherproof - IP65)

Any ideas why the 2 cable sizes are quoted?

 

[Spark123]

How long is the run?
One answer is volt drop - the longer the run the bigger the cable is needed.
Other things like grouping, ambient temp, buried underground and thermal insulation also play a part in cable selection.

 

[pte440]

i am assuming that 8kw is the output, therefore its input would be around 3kw maximum, 4mm or 6mm would be fine, 2.5mm would be pushing it a little, you wouldnt need a 63a isolator, 25a would be fine

 

[Steve]

i am assuming that 8kw is the output, therefore its input would be around 3kw maximum, 4mm or 6mm would be fine, 2.5mm would be pushing it a little, you wouldnt need a 63a isolator, 25a would be fine

If this were the case, a 13 amp plug would suffice!

However, if it is a whole-house heat pump system, then 8kw would be more realistic.

 

[Woslights]

The cable run in total in 22m, the input max is 8kw

 

[Lectrician]

6mm would be fine, depending on the length and size of your submain you have already installed.

6mm vers 10mm is not a huge price difference, certainly noticeable.

I would be happy with either size. bigger is always better.

 

[Stoday]

Presumably it uses an invertor, so there's no starting transient.

If it's direct on line start, does the 8kW max mean the starting or running current? If the running current, the cable would need to carry the higher starting current and the 10mm² cable might have been chosen for the volt drop under starting conditions. The electrician choosing the 6mm² cable may not have taken the starting transient into account (if there is one).