Volt Drop table help

[soulman]

Hi,

I was calculating volt drop today using xlpe armoured cable, 3 core, single phase. Table 4E4A pg 373. I am using 3 core cable but on single phase, so i would assume column 3 for single phase. I was told by the tech helpline although the cable is being used for single phase that column 4 should still be used as it is the number of cores that is the factor. Can anyone tell me why?

Cheers

 

[westward10]

Theoretical the third core can affect the current carrying capacity of the other two cores as it restricts heat dissipation which would increase the conductor resistance but I would say it is negligible. There is a case that for Table 4E4A for the current carrying capacity you should use the columns for a three phase supply if you are using a three core cable on single phase, again I would think this is negligible, I suspect this is the reason.

 

[Pete999]

Theoretical the third core can affect the current carrying capacity of the other two cores as it restricts heat dissipation which would increase the conductor resistance but I would say it is negligible. There is a case that for Table 4E4A for the current carrying capacity you should use the columns for a three phase supply if you are using a three core cable on single phase, again I would think this is negligible, I suspect this is the reason.

What he said

 

[telectrix]

but he's referring to VD, not CCC.

 

[westward10]

but he's referring to VD, not CCC.

Yeah I know but the voltage drop would be affected by the third core restricting heat dissipation. I added the ccc bit because it has the same affect.
Looks like I worded it poorly.

 

[HandySparks]

Yeah I know but the voltage drop would be affected by the third core restricting heat dissipation. I added the ccc bit because it has the same affect.
Looks like I worded it poorly.

The effect will be trivial. After all, the third core's not normally carrying any current.

 

[westward10]

The effect will be trivial. After all, the third core's not normally carrying any current.

Like I said it is negligible but that is the reason, the fact it is not normally carrying current is not important.

 

[soulman]

Hi, Thank you for replies. After looking into this further, I have decided that the tech line was incorrect. The column that should be used, is column 3 for single phase. The third conductor will only carry current under fault conditions, therefore having no bearing on volt drop.

Cheers

 

[westward10]

Hi, Thank you for replies. After looking into this further, I have decided that the tech line was incorrect. The column that should be used, is column 3 for single phase. The third conductor will only carry current under fault conditions, therefore having no bearing on volt drop.

Cheers

I agree with them though the effect of the third core would be debatable.

 

[soulman]

Hi Westward, i spoke to an electrical designer. He told me, if I look in the regs, i'll see that there is no difference in volt drop between between 3 or 4 core cable as it is presumed that 4 core will be supplying 3P & N. The load should be balanced therefore no current flowing in the neutral, 4th core.

Cheers

 

[westward10]

Originally you were using three core for single phase with the third core as a cpc and as such columns for three phase should be used due to the negligible effect of the third core.
As for a three phase circuit being balanced and the neutral carrying no load may work in Utopia but in practice this is highly unlikely. Whether it carrys load or not its presence will affect the other conductors.