A/C installation "outdoor to indoor" cable query

[Ian1981]

For disconnection times quicker than the stated 0.1 seconds given in appendix 3 the let through energy from the manufacturer of the mcb would be needed.
So K2 x S2 must be equal to or greater than the I2t let through energy of the mcb for fault protection and tho damage doesn’t occur to the cable.
As an example from hager a type b and c I2t value for a 32 amp mcb is 29kA for a 6ka device.
S0 1.5mm should be fine given 1.5x1.5 =2.25 x 115x115 = 29,756.25 so 1.5 mm is protected in this example.

Edit substituting 29kA in the Adiabatic equation gives a size of 1.48mm for compliance so 1.5 scrapes in.

 

[PEG]

As pete said,most of these are fed from an internal board,which has its own protection,applicable to the csa of the cable used. As does the 120W circulatory pump,on a 8kW electric boiler.

 

[Strima]

It was SY multi flex

Used outside?

 

[Zdb]

Yep used outside. It seems to be the cable of choice for these A/C engineers.

 

[Strima]

SY is not suitable for use outside as it has very poor UV resistance and is not water resistant.

After a few years the outer sheath cracks and the steel braid starts to rot.

 

[Zdb]

Agreed, however I see it being used all the time on A/C installs for the interconnection between the outdoor/indoor unit.

I'm guessing the cable needs mechanical protection because it passes through a wall and they don't want to use an RCD for obvious reasons. Also you can't really use SWA as going by what I saw yesterday there's nowhere to terminate a gland.

Both the indoor and outdoor units had a cable grip so nowhere to put compression / SWA glands.

 

[Zdb]

Also from what I saw they don't even attempt to earth the braiding they just cut it off.


Anyone come across this when looking at A/C installs?

 

[Strima]

Do they need mechanical protection? Most A/C units I've seen are close to the wall so very little risk of impact damage.

Also the braid should be earthed at the supply end.

I'd be leaning towards using H07 cable for this type of application.

 

[Pete999]

Do they need mechanical protection? Most A/C units I've seen are close to the wall so very little risk of impact damage.

Also the braid should be earthed at the supply end.

I'd be leaning towards using H07 cable for this type of application.

I think what people need to realise is HVAC Mechs are a trade in their own right, and rightly so, whilst they are aware of the dangers of refrigeration gases, and the correct handling of a dangerous item, they tend to stick to their trade, and go with the flow regarding the electrical side of their industry.
Until the manufacturers of split A/C systems, align themselves withe vagaries of BS 7671 we will always get these anomalies, as to what is the correct type of wiring needed to interlink the inner and outer parts of the system, remember most of the "Split systems" come with the interlink cabling included in the package, so with some experience in this area I would suggest that the IET and A/C manufacturers get together and iron out the correct way to install these systems, until they do we will always have this problem, blime a long post there Pete, take another sip.

 

[Ian1981]

Only use of earthing the braid is for it to act as screening as far as I’m concerned as it’s no good for taking fault current and is unsuitable to be used as a cpc in its own right.
It offers very little mechanical protection to the cable.

 

[multimick]

Only use of earthing the braid is for it to act as screening as far as I’m concerned as it’s no good for taking fault current and is unsuitable to be used as a cpc in its own right.
It offers very little mechanical protection to the cable.

seen a couple of hot tubs recently which specified sy cable from commando plug to hot tub

 

[Leesparkykent]

Never seen AC units where the indoor cassette is powered from the condenser. Usually just a control cable for signalling with the cassette on a fused spur and condenser on its own supply.

 

[Pete999]

Never seen AC units where the indoor cassette is powered from the condenser. Usually just a control cable for signalling with the cassette on a fused spur and condenser on its own supply.

Just another way of doing it Lee, problem being AC/HV blokes don't always look at it that way, try and keep it all under one roof, so to speak, but yes seen it that way many times.

 

[Leesparkykent]

Just another way of doing it Lee, problem being AC/HV blokes don't always look at it that way, try and keep it all under one roof, so to speak, but yes seen it that way many times.

Yes mate we have recently started taking on the mechanical side of things so it's all under one roof.

 

[Pete999]

Yes mate we have recently started taking on the mechanical side of things so it's all under one roof.

Got your Gas safe handling qualification then?