VRV Power sypply cable

[kvas]

Hi everyone, i have a question, i have to install a vrv and i read to the manual that i need a cable 1,5mm^2 only and 16A fuse at the aoutdoor units. its a 5,5 kw unit ( mhi pumy-p140 3-phase) i thought that is a little small and i ask help from some engineers. three of them said of course 4mm^2 .. my god!!! 4 of them 2,5 mm^2 and none 1,5mm as manual propose. what is happening here!!! i know that the equation is : Ι=5500/380*1,73*~0,8= 10A therefore 1.5mm^2. the engineer that says 4mm^2 is strict with me and this scaring me . its the time to ask someone professional who is here.!!:mad:

[frank]

That is the wrong formula for cable sizing.

You need to give us the length of the cable between the distribution board and the condensing unit, the maximum rated FLC from the manufacturers data plate and the method of installation for us to be able to give you a definative answer.

[kvas]

http://pdfcast.org/pdf/electrical-data-mhi-vrv
the length is about 20 mtrs from distribution board. which is the correct formula . please dont tell me only a number of cable size! and thx you!

[frank]

Assuming that you are using Armoured cable to BS6346 clipped direct. (Reference Method C)

Step 1

Select your protective device to be equal to or greater than the circuit design current In (from your data = 8.51A FLC), so a 10A MCB will do the job. Make it a Type 3 (or C) with a motor rated disconnection curve.

Step 2

Calculate the current carrying capacity of the cable to be used (It) from the formula shown in Proceedure 2 (below). The cable must be rated equal to or greater than the protective device,In and these derating factors, if applied will increase the current carrying capacity of the cable.

Step 3

Select the cable to be used based on the value in step 2 from Table 4D4A. Column C indicates that a 1.5mm2 three or four core for 3 phase A.C. can carry 18A.

Step 4

Determine that the volt drop in the cable is less than 5% (400 x 5% = 20)(Appendix 12 BS7671-2008) from the formula (below)

So: Vd = (mV/A/m x Lb x L) / 1000 =

(31 (Table 4E2B) x 8.51 x 20) / 1000 = 5.276V

5.276V is less than 20V (less than 5% of 400V) so a 1.5mm2, 3 or 4 multi core armoured cable, clipped direct onto a wall in an ambient temperature not exceeding 30C will be OK for your installation.

64896490

[kvas]

You are amazing man!! thank you al lot, not for the answer but for the lesson!!