A/C installation "outdoor to indoor" cable query

[Zdb]

So I went to a job yesterday where the A/C engineers had upgraded an air conditoning system and fitted new units. I was there just to switch on the power and do the testing and certification on the electrical side of things.

They used the existing supply cable from the old unit (6mm) and MCB (B32).

The bit that confused me was that the cable going from the outdoor unit to the indoor unit was only 1/1.5mm.

Surely this is too small for the 32a MCB or am I missing something?

Please can someone advise as I don't usually get involved in A/C installations.

Thanks.

 

[Toneyz]

We have got this set up on a job we are on at the moment where a 6.0mm SWA goes to outdoor unit and they have run 1.0mm flex to indoor unit I assume that it is internally fused.

 

[telectrix]

the load of the internal unit is a fixed load within the ccc of the 1.5mm or whatever cable is used. therefore overload protection for this cable is not needed.just s/c protection, which is provided by the 32A.

 

[Pete999]

All the cable fro condenser to evaporator does is run the fan in the evaorator and is internally protected.

 

[telectrix]

even if it isn't, it's OK.

 

[Pete999]

even if it isn't, it's OK.

Morning Tel

 

[telectrix]

ditto, pete.

 

[Wilko]

Hi - don't suppose you noted the AC model ?
Just thinking it might be worth looking at manufacturers doco.

 

[Spoon]

Depending on cable type, if the cable is 1mm isn't that too small, according to table 52.3 of the regs?

 

[Wilko]

Yes, but perhaps relying on manufacturers spec as its flex (last section of that Table)

 

[Spoon]

Yes, but perhaps relying on manufacturers spec as its flex (last section of that Table)

True mate. The OP didn't specify what cable it was. That's why I put 'Depending on cable type'

 

[telectrix]

True mate. The OP didn't specify what cable it was. That's why I put 'Depending on cable type'

do you mean round or flat?

 

[Spoon]

Not sure what the regs mean by 'flexible cable' as all cables are flexible...when you bend them enough....

 

[Wilko]

At risk of being a goody two shoes here, but I'm concerned that 1mm may not survive a low Zs sc on C32 (?) without damage if it was already running hot. Perhaps apply adiabatic?

 

[Zdb]

It was SY multi flex

 

[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?

 

[Leesparkykent]

Got your Gas safe handling qualification then?

No I'm doing my gas safe ATM but we Have gas safe plumber and F-gas aircon guy cards in.

 

[Zdb]

I did my F-gas but steer clear of A/C work tbh. Best to stick to your own trade.

So out of interest what type of cable do people recommend for this interconnection? Would need to be a multicore flex suitable for outdoor use.

 

[Zdb]

NYY-J / H07RN-F?

 

[Zdb]

So what is the best type of able to use for the interconnection?

I keep seeing AC engineers using SY outside and I'd like to offer them a better alternative.

 

[Zdb]

Keep seeing the same old SY cable that looks pretty prerished

 

[Amp David]

All they do is act as a comunication wire telling the condenser to kick in i thought. Howcan it become overloaded?

 

[Pete999]

All they do is act as a comunication wire telling the condenser to kick in i thought. Howcan it become overloaded?

And a supply to the Evaporator Fan.

 

[mydigitalhome]

Interesting, so a SY is a deviation of the regs as main supply cable for fixed wiring which should have been identified on the electrical certificate too. Covered in the cinema today.

 

[Pete999]

Interesting, so a SY is a deviation of the regs as main supply cable for fixed wiring which should have been identified on the electrical certificate too. Covered in the cinema today.

"A departure" to be exact

 

[Zdb]

We shouldn't be putting any departures down really. No more SY cables for AC interconnection then?

 

[Toneyz]

We shouldn't be putting any departures down really. No more SY cables for AC interconnection then?

You have to document why the departure is no less safe than complying with BS7671.

 

[plugsandsparks]

I generally use YY for interconnections, SY is way to hard when you get to the indoor unit, also it looks a mess. Outside the YY generally follows the pipework so i hide it within the overall clump and tape it all up with pipe insulation tape, thereby no UV, mech damage is negligable.
BTW the fixed testing to BS7671 is to the outdoor unit isolator, everything else is MIs.
For multis, i use a outdoor grade Cat5 or 6 between outdoor and indoors as its got a much better sheath.

 

[Spoon]

 

[Amp David]

Why does everyone love sy. I sub to another company and if its not armoured its sy, why i just dont know.

 

[Toneyz]

Why does everyone love sy. I sub to another company and if its not armoured its sy, why i just dont know.

Its easier to install.

 

[Strima]

SY is very good in certain applications and environments. However people tend to use it outside or bury it thinking it's the same as SWA.

It's used a lot in telecoms as it's ideal for use in switch rooms etc. However I have seen some very poor use of this cable, especially outside and I have seen how badly it suffers and degrades.

 

[plugsandsparks]

Best i have seen is SY being used for supply from a generator to a machine , outside on a gravel plant. The cable had to be removed every night because it kept getting stolen. A telehandler was used to transport it to a lock up. They dont last long when used and abused.