Resistance per Meter for copper cable (R1+R2)
 

Hi

Can someone help out with this Electrical problem.
(I'm doing a CG2330 course)

Table 9A of the IEE On site guide only goes upto 50mm csa cable for the
values (R1+R2)

Eg
50mm Phase+CPC = 0.774 mOhms/m

What would you do if the conductor was say 70mm ???

Is there a formula I could use ?


Thanks

Leigh

Resistance per Meter for copper cable (R1+R2)
 

wrote in message
oups.com...
Hi

Can someone help out with this Electrical problem.
(I'm doing a CG2330 course)

Table 9A of the IEE On site guide only goes upto 50mm csa cable for the
values (R1+R2)

Eg
50mm Phase+CPC = 0.774 mOhms/m

What would you do if the conductor was say 70mm ???

Is there a formula I could use ?


50/70 x 0.774 mOhms/m?

Resistance per Meter for copper cable (R1+R2)
 

"dennis@home" wrote in message
o.uk...

wrote in message
oups.com...
Hi

Can someone help out with this Electrical problem.
(I'm doing a CG2330 course)

Table 9A of the IEE On site guide only goes upto 50mm csa cable for the
values (R1+R2)

Eg
50mm Phase+CPC = 0.774 mOhms/m

What would you do if the conductor was say 70mm ???

Is there a formula I could use ?


50/70 x 0.774 mOhms/m?

Nope, nothing like.
Its cross sectional area you need to use (pi * r^2)

So for 50mm = approx 1962 sq mm, 70 mm = approx 3846 sq mm.

i.e. it will be arount HALF the resistrance or about 385milliOhms/metre.

Slurp

Resistance per Meter for copper cable (R1+R2)
 

"Slurp" wrote in message
...

"dennis@home" wrote in message
o.uk...

wrote in message
oups.com...
Hi

Can someone help out with this Electrical problem.
(I'm doing a CG2330 course)

Table 9A of the IEE On site guide only goes upto 50mm csa cable for the
values (R1+R2)

Eg
50mm Phase+CPC = 0.774 mOhms/m

What would you do if the conductor was say 70mm ???

Is there a formula I could use ?


50/70 x 0.774 mOhms/m?

Nope, nothing like.
Its cross sectional area you need to use (pi * r^2)

So for 50mm = approx 1962 sq mm, 70 mm = approx 3846 sq mm.

i.e. it will be arount HALF the resistrance or about 385milliOhms/metre.


Cables are usually quoted in mm2.
It correct for 50mm2 and 70mm2 is it not.

Resistance per Meter for copper cable (R1+R2)
 

Slurp wrote:

"dennis@home" wrote in message
o.uk...

50/70 x 0.774 mOhms/m?

Nope, nothing like.
Its cross sectional area you need to use (pi * r^2)

No, the figures mentioned were clearly conductor CSAs in mm^2, so the
answer was right, at least for DC.

An easier way would to use the tabulated values for 35mm^2 and halve
them, giving 0.524 mohm/m for R1+R2 for 70+70 mm^2.

However the OP should be aware that for these large sizes used on AC the
impedance will be higher then the DC resistance because (a) skin
effect increases the resistance and (b) the inductive reactance is not
necessarily negligible. The OSG is only relevant to installation work
up to 100 A per phase, in which you would not usually need to use 70
mm^2 conductors!

--
Andy

Resistance per Meter for copper cable (R1+R2)
 

"dennis@home" wrote in message
.uk...

"Slurp" wrote in message
...

"dennis@home" wrote in message
o.uk...

wrote in message
oups.com...
Hi

Can someone help out with this Electrical problem.
(I'm doing a CG2330 course)

Table 9A of the IEE On site guide only goes upto 50mm csa cable for the
values (R1+R2)

Eg
50mm Phase+CPC = 0.774 mOhms/m

What would you do if the conductor was say 70mm ???

Is there a formula I could use ?


50/70 x 0.774 mOhms/m?

Nope, nothing like.
Its cross sectional area you need to use (pi * r^2)

So for 50mm = approx 1962 sq mm, 70 mm = approx 3846 sq mm.

i.e. it will be arount HALF the resistrance or about 385milliOhms/metre.


Cables are usually quoted in mm2.
It correct for 50mm2 and 70mm2 is it not.

Yes you are right. I was going by the OP's spec of 50mm/70mm, not thinking
it was mm2!

Have a team point and gold star.

Slurp

Resistance per Meter for copper cable (R1+R2)
 

On Tue, 25 Oct 2005 17:16:15 GMT, "dennis@home"
wrote:


"Slurp" wrote in message
...

"dennis@home" wrote in message
o.uk...

wrote in message
oups.com...
Hi

Can someone help out with this Electrical problem.
(I'm doing a CG2330 course)

Table 9A of the IEE On site guide only goes upto 50mm csa cable for the
values (R1+R2)

Eg
50mm Phase+CPC = 0.774 mOhms/m

What would you do if the conductor was say 70mm ???

Is there a formula I could use ?


50/70 x 0.774 mOhms/m?

Nope, nothing like.
Its cross sectional area you need to use (pi * r^2)

So for 50mm = approx 1962 sq mm, 70 mm = approx 3846 sq mm.

i.e. it will be arount HALF the resistrance or about 385milliOhms/metre.


Cables are usually quoted in mm2.
It correct for 50mm2 and 70mm2 is it not.


The OP stated 50mm csa - csa = cross sectional area. For a direct
current, resistance is inversely proportional to the cross sectional
area of a material so doubling the area halves the resistance.

Mr F.

Resistance per Meter for copper cable (R1+R2)
 

Hmm, looks like I've opened up a can of worms here !

Here's the full example question and the the bits I've got to.

Consumer unit, 190V A.C., with BS3036 fuse, Ze=0.49Ohms
45m PVC Armoured cable, clipped directly to wall with 5 other circuits
50 Degree C ambient temp, 9Kw load
Cable runs through 100mm Insulation

IB = 9*103/190 = 47.36Amps

In = 60A (From Page 195 Fig3.2A Next biggest to 47A)

Correction Factors

1). Cf - A BS3036 device 0.725
2). Cg - From Table 4A1, (Page 210) Method 1 used
From Table 4B1, 1+5=6 Circuits, Bunched = 0.57
3). Ca - From Table 4C2 50°C, Armoured PVC = 0.87
4). Ci - From Table 52A, page 97 100mm = 0.81

Iz = 60 = 206Amps
(0.725*0.57*0.87*0.81)

From Table 4D4A, Armoured PVC, Method 1, Single Phase, 222A nearest

70mm2 csa conductor

Then the problem, table 9A O/S/G only goes upto 50mm

Table 9A (Page 158) of the O/S/G gives mO per meter values to
calculate R1 + R2

R1+R2 = mO/m * Length (m) * Temperature multiplier (Table 9C)
1000

So I'm a bit confused as to who's right.

Leigh

Resistance per Meter for copper cable (R1+R2)
 

Resistance per Meter for copper cable (R1+R2)
 

Hi Andy

The values were just picked out of the air by the lecturer, it was so
that the class could work through correction factors, finding out Zs,
fault currents and selecting cable sizes.
I think he left out all the details so that our poor little brains
don't overload :-), but the values he used cause more problem in the
end.

Thanks for information, helps move class room knowledge to the real
world (Even if the above example would never happen).

Leigh

Resistance per Meter for copper cable (R1+R2)