Quick Question

[RF Lighting]

I seem to have my thick head on this evening.

Just doing some cable calcs for a job, but I can't find the table in the regs for resistance of copper conductors per meter.

Can anyone make me look really silly, and point me in the right direction?

 

[Spark123]

On site guide or GN3

 

[RF Lighting]

That'll be why I can't find it then

Ta very much

 

[ricicle]

Or GN8 (which I received from the IET yesterday) and is a good read.

 

[securespark]

Or GN8 (which I received from the IET yesterday) and is a good read.

If you can't get to sleep!

 

[Spark123]

Is that to the 17th edn?

 

[securespark]

What, the sleeping?

 

[Spark123]

Didn't see your post there simon
I'm still waiting for the update sheet to the 17th for gn8

 

[ricicle]

Is that to the 17th edn?

Not with some of the terminology they are using in there (EEBADS), but all the principles are still the same.

 

[ericmark]

V/A = ohms so v/a/m = ohms per meter. So for example 18mV/A/m = 0.018 ohms per meter for 2.5mm

 

[ban-all-sheds]

Or there's a dead handy table in the little Amicus guide.

 

[Spark123]

Amicus is called Unite this week

 

[ColJack]

V/A = ohms so v/a/m = ohms per meter. So for example 18mV/A/m = 0.018 ohms per meter for 2.5mm

that's not right is it?

for a start the mV/A/m varies depending on whether it's 2 cables or 3 or 4 cables..

table 9A in the OSG gives the resistance pre meter or 2.5 as 7.41milliohms/meter..

 

[Spark123]

for a start the mV/A/m varies depending on whether it's 2 cables or 3 or 4 cables..

Yep, this is at the conductor operating temperature i.e. 70 deg or 90 deg depending on cable type, also takes into account the resistance/impedance of both the phase conductor and neutral conductor in the case of single phase, or the phase conductors in 3 phase.

table 9A in the OSG gives the resistance pre meter or 2.5 as 7.41milliohms/meter..

Yep, for a single length of copper wire on its own at 20 degrees.

 

[LiamPope]

It's OK to use the volt drop table as Eric did so long as you remember it is also considering the return down the neutral - i.e. twice the length of cable as the 7.41mOhm figure you quoted from table 9A for a single conductor. To compare like for like, the appropriate figure from table 9A would be the 14.82mOhm figure that relates to the 2.5mm^2 conductor and a 2.5mm^2 CPC. The reason they are not exactly the same (14.82 vs 18) is that table 9A figures are for 20 degrees, wheras the volt drop table figures are for 70 degrees where the resistivity of copper is higher, hence the higher resistance.

Liam

Edit - beaten to it!