Cable Calc help please...

[Sparky83]

Hi,

I need to install a supply for a new coffee machine. It is 6.9KW = 30Amps

It will be a 40mtr run

I think i have this right but my calculator is playing up a bit,

Ib = 6900/230 = 30A

In = 32A

In / CgxCa = Iz 32/0.88x40 = 0.9

Iz = 32+0.9 = 32.9A


Page 338 in the green Regs...

Reference Method E, Column 4

4mm Cable @ 41A

Volt Drop...

40(mtrs) x 30 x 11 / 1000 = 13.2v (which is not allowed)

6mm Cable @ 53A

40(mtrs) x 30 x 7.3 / 1000 = 8.76v (Which is allowed)


So am i right in saying that 6mm is the way to go?

the bit in red is where im must unsure

Also one further question, on page 338. column 4 it says 1 two core cable, single phase, ac or dc

But my cable will be 3 core including the earth?

The next column says 3 cor cable but than says 3 phase??

Am i right in using column number 4?

thanks

 

[telectrix]

you don't say what type of cable. the table on p338 is for SWA. if you are using T/E, its table 4D5 on p340. other than that, you are right to go with 6mm

 

[Sparky83]

Sorry yes, SWA is the cable of choice.

So the calcs are all correct?

 

[spark 68]

You would calculate this as 2 core, as your CPC does not normally carry any current.

As others 6mm^

 

[stujham]

Got to ask,

Would you not go one step further and work out the minimum CSA of cpc for circuit design using Adiabatic ?

 

[spark 68]

I believe the Voltage Drop was the limiting factor in this case, hence the 6mm^, rather than CPC size or CCC of the cable, (4mm^ was enough for the CCC and CPC size)
So no need for the adiabatic calc.

 

[yellowvanman]

Why not use 2 core SWA?

 

[Sparky83]

You would calculate this as 2 core, as your CPC does not normally carry any current.

I thought that this was the case, just wanted to have it confirmed.

Also is the part in Red correct?

 

[Sparky83]

Why not use 2 core SWA?

Good point! Although i "think" we may have some 6mm armoured.

 

[Guest123]

Also is the part in Red correct?

Where have you picked the values for (Ca) & (Cg) from???

 

[Sparky83]

Where have you picked the values for (Ca) & (Cg) from???

I got them from the OSG, as i didnt know the ambient temperature or if there were any cables due to not being able to see it myself yet i when for the worst case for each.

Its quite possible there s going to be other cables along parts of the route and as part of the cable run is above the false ceiling of a commerial kitchen it my be a little warmer than the norm, again hence i went for the worst case.