Is the interconnecting cable between outdoor and indoor AC units classed as a control cable or power cable?

Could be either ... or both.

It's certainly part of 'machinery' as defined in the Supply of Machinery (Safety) Regulations, and therefore not completely in the scope of BS 7671 ...

• I believe it should be in scope of BS7671, as someone needs to certify it on install as compliant, and any cables used for Power should comply with BS or harmonised standards

Not sure about that - there is no reason a competent person cannot install to the relevant machinery standard by following well written maker's instructions, which may need you to do things that are not be as simple as BS7671.
Actually we already see this with things like heating controller wiring and alarms and so on, where '7671 does not really cover the situation. As a very noddy example how would you test a Honeywell Y plan boiler installation to BS7671 ? Concepts like Zs go out of the window with 3 way valves stalled in mid position with diodes across micro-switches.Usually, as the boiler is considered an appliance, so you don't test the installation components, just the whole thing.

David Alcock said:

I believe it should be in scope of BS7671, as someone needs to certify it on install as compliant

Compliant with what? I agree with Graham, there seems little doubt that the cable is connecting two parts of a machine.

Let's suppose that your friendly local sparks installs a new circuit which terminates in an isolator. He (or she) notifies the new circuit to building control. That is BS 7671 sorted.

Householder then pops down to Screwfix and wires in the ACU. There may be a requirement to notify under another part of the building regulations, but that is not what we are talking about here.

Without some kind of entry in BS7671 it leave the engineering judgement open to the Designed and/or the Installer.  Now let me put this question forward.

In the UK have you seen an AC unit with wiring outside using SY or CY cable?  If so how will that cable deal with UV from the sun?  Does the MI specifically forbid SY/CY cable outside and recommend/demand a HO5 or 7 variant?

wiring outside using SY or CY cable? 

Plenty, and we use a lot of SY at work for voltages well above mains because of the RF shielding properties. Over a decade or so, if fully exposed to sun, and most is not, I'd expect SY failures at the clear jacket, and one can see the steel wires begin to rust where the outer has opened, and after perhaps another decade the shielding efficiency is lost. At that point it is pretty much as good as permanently installed  arctic flex.

There is a lot of '7671compliant surface mounted and catenary slung twin and earth and arctic style PVC cable as well, that slowly embrittles, cracks and fails on a similar timescale. 

As SY actually reveals it is failing, by the discoloration as the inner cores rust I personally like that inspectable quality. What I do not like is that almost no-one seems to have bothered to learn  what to do with the braid in termination. 

I think it is a bit silly and unfortunate that there is no BS recognised standard for SY and CY cables, but they have their place (out of the sun, ideally).

Mike.

Sergio Fernandez said:

recommend/demand a HO5 or 7 variant?

Be careful with those cable specs - H only means it's a harmonized type, 05 or 07 the voltage range - so nothing there specifies UV resistance at all.

  - Andy.

AJJewsbury said:

recommend/demand a HO5 or 7 variant?

EG    H07RN-F

H07RN-F cable is UV resistant and suitable for long-term outdoor use, including direct sunlight exposure. Its robust PCP (polychloroprene) sheath protects against environmental, chemical, and mechanical stresses, making it ideal for industrial, agricultural, and construction applications

Key features regarding durability include: 
 - Weather Resistance: Designed to withstand exposure to sunlight, moisture, and extreme temperatures (-30 - +60 degrees celcius).
 - Structural Integrity: The UV-resistant outer sheath prevents the material from drying out, cracking, or bursting when exposed to sunlight.Versatility: 
 - It is oil-resistant and flexible, commonly used for connecting machinery, heavy-duty tools, and temporary power supplies in open air

AJJewsbury said:

recommend/demand a HO5 or 7 variant?

EG    H07RN-F

H07RN-F cable is UV resistant and suitable for long-term outdoor use, including direct sunlight exposure. Its robust PCP (polychloroprene) sheath protects against environmental, chemical, and mechanical stresses, making it ideal for industrial, agricultural, and construction applications

Key features regarding durability include: 
 - Weather Resistance: Designed to withstand exposure to sunlight, moisture, and extreme temperatures (-30 - +60 degrees celcius).
 - Structural Integrity: The UV-resistant outer sheath prevents the material from drying out, cracking, or bursting when exposed to sunlight.Versatility: 
 - It is oil-resistant and flexible, commonly used for connecting machinery, heavy-duty tools, and temporary power supplies in open air

Exactly my question, this specified by the manfacturer, which distribute the same equipment around the world, ive never seen  this cable used in the UK for AC interconnections, but, this cable is not LSF so not suitable in some locations

To another point on the design of the machine, it's also a requirement to design the installation and certify it, along with conplying with the UK regulations

Might be wroth speaking with Doncaster Cables Technical team?

Tel 01302 821700

email sales@doncastercables.com

website.   https://doncastercables.com

David Alcock said:

To another point on the design of the machine, it's also a requirement to design the installation and certify it, along with conplying with the UK regulations

With respect, you seem very reluctant to specify the standard or even law against which you are certifying compliance. Why is that please?

There are lots of regulations to comply with, BS7671, BS 5839, HTMs, and lets not forget the EAWR and CDM

Some makes of HO7 will be more or less UV resistant - its the letters that follow that matter.;-) 

UV resistant Look out for third letter "N" without trailing qualifier numbers

(See https://www.peakcables.co.uk/european-system-cenelec-codes/ for a fuller cable decoding of the system or even 

https://myelectrical.com/notes/entryid/228/harmonised-cable-codes-and-colours 

Then see https://myelectrical.com/notes/entryid/178/cable-insulation-properties for the chemical and physical properties of most common insulation materials.)

 Polychloroprene (brand name Neoprene synthetic rubber) on its own is rather better than say  PVC,  or indeed un-stabilised polypropylene or polyethylene, but even so  mil-spec versions exist that also have additional  UV stabilizers  put in to survive long term in the sun- 

As a rule of thumb then unstabilised  PP or PE in full desert sun for about a year has lost 70% of flexibility and will show crazing and cracking right through if flexed

PVC loses its chlorine from the surface and slowly crazes with the damage stopping after a few mm, unless the cracks are opened by flexing to allow the UV deeper.This is over a couple of years of full desert sun exposure.

N on the other hand is dark so the UV does not penentrate and develops surface crazing due to loss of surface flexibility over about 5 times that period

It is worth knowing what you are selecting. All cables last better out of sunlight but in the UK most days are not desert sun levels of UV , and even the 'wrong' cables can last many decades if at least partly shaded.

Mike.

Which applies depends upon what you are doing, but why are the cables troubling you so much?

Home many machines are being installed, one or two please?

EG    H07RN-F

Indeed- but not say H05VV-F (which is ordinary 3183Y PVC flex) - that was my point.

   - Andy.

I dont believe there is one standard alone that you need to consider, its in some degree in my opinion that if you use just one i.e. manfacturers recommendation then it may fall fiul of other uk regulations or locations where you are installing the cable, so its engineering judgement, My judgement is it should be a power rated cable and type to suit the environment

For example, recently a contractor submitted data sheets for a cable that was not LSF in an environment that required it, and after its rejection another cable chosen was the same standard of cable but LSF whilst also being of the same standard to the manufacturers recommendations

H07RN-F not LSF to H07ZZ-F so for AC interconnector its power rated as supplies the indoor unit snd suutable for externsl use and LSF

David Alcock said:

I dont believe there is one standard alone that you need to consider, its in some degree in my opinion that if you use just one i.e. manfacturers recommendation then it may fall fiul of other uk regulations or locations where you are installing the cable, so its engineering judgement, My judgement is it should be a power rated cable and type to suit the environment

This is also true ... the installation of the cable is Construction Work as defined in CDM Regulations, and therefore, particularly for places of work, there are safety factors to consider.

However, some of the environmental and safety factors might include EMC ... so if the manufacturer recommends a cable like CY or SY for EMC purposes, then a suitable alternative arrangement of a wiring system is needed ... it could include, for example, cables in metallic conduit or trunking that provide an equivalent EMC performance. See also Section 444 of BS 7671, and BS IEC 61000-5-2.

Agree