So are Samsung refusing a warranty replacement on the basis that it wasn't installed correctly, and this has caused the failure, thus passing liability to the installer? 

How long is the workmanship warranty provided by your installer?

I haven't taken the case off to look at my data cable, but externally it looks very much like a CAT5/CAT6 network cable. I'm due to service my outside unit soon, so I'll try to remember to have a look at that end of the cable when I have the cover off for the electrical inspection.

EDIT: Additionally, the 'heating engineer' would not have done the electrical connections - that would normally be done by an electrician who would be at fault. Likely the same company though.

Hi Old_Scientist.  Samsung are saying tne use of an unapproved cable invalidates the warranty.  The use of a 2 core CY data cable has been specified from day one of these Samsung Units and is clearly specified in the installation manual.  Therefore, yes...they are saying it's down to the installer.  I would personally say, if it's that important for the correct functioning of the system, why isn't the cable supplied as part of the installation kit in the first place? It would cost Samsung pennies.

The engineer I have spoken to at Samsung said the use of unshielded cables has caused a LOT of issues such as mine.  There is obviously still a major transition from traditional boilers to heat pumps and I wonder if a lot of electricians simply don't understand the importance of installing the correct cable?

Posted by: @steveimpey

↑

...

Having spoken to Samsung, their first question was to ask about the cable that runs from the F1 and F2 terminals. Upon my electrician checking it appears 4 core cat 6 data cable was used instead of the the 2 core shielded CY data cable specified by Samsung. This has lead to the communication chip on the PCB having to work much harder due to "noise" which has resulted in it's failure.

...

Are you able to look at that Cat6 cable still? What does it say on the side? It would be interesting if what your installer used was Cat6 STP (Shielded Twisted Pair) rather than UTP (Unshielded Twisted Pair), since if it really was STP then I can't see how Samsung's argument could hold up. Please note that I'm talking as someone with a little understanding of computer networking, not of heating system wiring, so I'm not making any definite judgements.

@majordennisbloodnok  The unit is all sealed up again.  I have an electrician coming out on the 23rd July.  

From my limited knowledge Cat 6 cable (whether shielded or not) is designed to carry only microscopic amounts of computer data. Because of this, the copper wires inside are extremely thin (usually around 23 AWG, which is about 0.25mm²).

​Samsung’s official wiring guide demands a much thicker 0.75mm² or 1.0mm² wire. Because the Cat6 wire is so thin, it has much higher electrical resistance. Over a long run, this causes voltage drop. The digital signal loses its strength by the time it travels from the inside controller to the outside unit, leading to communication dropouts, which in turn is made worse by other electrical interference.

@steveimpey, I wouldn't say Cat6 cable is only designed for small amounts of data; it's rated to 10Gb/second which I'd say is likely to be far higher than Samsung need. However, if they're specifying a particular gauge, they are obviously the ones who know their kit best and so are in a good place to judge. Distance could, I suppose, be an issue since Cat6 is only rated to 10Gb/s at runs below 50 metres, and it then becomes rated to Cat5 speeds (1Gbps) up to 100 metres. Far more likely, though, is the shielding issue.

Nonetheless, if it's sorted now, it's a moot point and certainly not an important enough detail to warrant much effort digging further.

Posted by: @steveimpey

↑

​Samsung’s official wiring guide demands a much thicker 0.75mm² or 1.0mm² wire. Because the Cat6 wire is so thin, it has much higher electrical resistance. Over a long run, this causes voltage drop. The digital signal loses its strength by the time it travels from the inside controller to the outside unit, leading to communication dropouts, which in turn is made worse by other electrical interference.

Well that's interesting.  If it needs fat cable it's because it's running a lot of current (V=IR) in which case it's much less likely to be affected by interference. I'm not sure I trust Samsung's explanation!

I thought Samsung used modbus which usually uses shielded twisted pair with a specific characteristic impedence, although I think you can run the protocol over alternative physical layers.

Posted by: @steveimpey

↑

​Samsung’s official wiring guide demands a much thicker 0.75mm² or 1.0mm² wire. Because the Cat6 wire is so thin, it has much higher electrical resistance. Over a long run, this causes voltage drop. The digital signal loses its strength by the time it travels from the inside controller to the outside unit, leading to communication dropouts, which in turn is made worse by other electrical interference.

If it's a data cable, current will be minuscule, voltage drop irrelevant.

If they run significant current through it then they should call it "power cable" not "data cable".

This has lead to the communication chip on the PCB having to work much harder due to "noise" which has resulted in it's failure.

Bullshit, they're just trying to dodge the warranty repair.

One reason for using 0.75mm² LIYCY cable is it can easily be terminated by electricians using standard tools, and it makes a reliable connection.

Cat5 wires are too thin for this: when used with screw terminals there is no strain relief, so vibration or just wiggling the cables around will break wires right at the screw terminal. Besides that, Cat5 works fine for RS485 (until the wires break, that is). Cat6 is a bit thicker so more robust, but really, anything thinner than 0.5mm² (AWG20) won't be reliable in screw terminals, and solid 0.5mm² is already fragile. Stranded 0.5mm² with ferrules is okay. Thin conductors really need a proper connector with strain relief, or other terminations like punch-in with a strap that holds the cable in place and prevent the wires from bending. 

Vibration from the compressor in the heat pump is enough of a reason to specify 0.75mm² stranded cable for data.

A valid reason for voiding the warranty due to using the wrong cable would be: Cat5 wire breaks off the terminal, then makes contact with something it shouldn't like mains voltage, and that would definitely fry the board.

@bobflux Just a thought, has a terminating resistor been fitted on the network cabling? The purpose of this resistor is to reduce the ‘noise’ in the system. Regards, Toodles.

If it is designed as a RS485 point to point link, then the designers should have included termination resistors on the board at both ends. No idea if they did though.

Posted by: @toodles

↑

@bobflux Just a thought, has a terminating resistor been fitted on the network cabling? The purpose of this resistor is to reduce the ‘noise’ in the system. Regards, Toodles.

It’s a valid question and worth getting an answer. However, just for maintaining clarity, that’s not strictly accurate. The noise from using unshielded cable near power cables comes from the interference generated by 230Vac running nearby. The resistor is to stop or reduce clean signal bouncing back along the wire once it’s hit the end. A resistor won’t clear up noise but will reduce reflection. Which is a form of noise, of course, but it’s worth not conflating the two.

Posted by: @majordennisbloodnok

↑

A resistor won’t clear up noise.

Is that the case? Surely the terminating resistor also reduces the impedance of the circuit, and thus induced currents will generate smaller voltages