Cable sizing for ASHP

[jfb]

I am installing a 6KW ecodan PUZ ASHP.

Looking to 1st fix the main cable to the ASHP.

It is a run of about 12m with insulation on one side of cable only.

In the manual it says it says 'Outdoor unit input capacity Main switch (Breaker)' as 16 A and minimum 3 x 2.5mm cable.

 

Does that mean the earth needs to be 2.5mm? (assuming it is one of the 3 cores)

Part of me thinks I should just put in a 4mm cable but I don't want to over specify unnecessarily.

 

Any one got an opinion?

 

 

 

[Carrerahill]

A 12m run of 2.5mm² Twin & Earth or SWA on a 16A breaker will be well within spec. No need to provide a 2.5mm earth. 

 

If you use a 2.5mm² T&E the CPC will be 1.5mm² - this is fine, if you use SWA you could use 2 core and the armour or 3 core and a core for earth and armour. 

 

Assuming this unit is outdoor, I would use SWA. 

 

 

Edited July 6, 2022 by Carrerahill

[jfb]

22 hours ago, Carrerahill said:

Assuming this unit is outdoor, I would use SWA.

Hadn't thought about this though I am hoping to get away without it since the isolator for the ASHP will be very close to the wall penetration so I presume I can get away with some suitable conduit.

[Carrerahill]

1 hour ago, jfb said:

Hadn't thought about this though I am hoping to get away without it since the isolator for the ASHP will be very close to the wall penetration so I presume I can get away with some suitable conduit.

You could, I would cost up the options though, by the time you put in suitable conduit, conduit glands & saddles you may find that ordering a length of 2 or 3 core SWA is about the same price and less hassle for the installing electrician as they just need to run in a cable, clip it and terminate it.  2.5mm SWA is not that expensive, you will get some saddles for 20p each and 2 glands for £5. 

 

Alternatively, mount the isolator on the house and bring the cable in the back (properly sealed with a grommet) and then run a piece of SWA from the isolator to the ASHP assuming it is indeed close enough.