calculation question

[stv292]

hi

the osg say's i can use 56m of cable of 1.0/1.0 installation method 103,101 e.tc. for lighting, on a radial at 6A. the mV/A/m is 44.
so 44x6x56/1000=14.7v that is 6% of lighting not 3%.
what am i missing

 

[telectrix]

you are using the rated current of the MCB rather than the actual load current, which may be quite a bit lower.

 

[stv292]

yes but you can have 13 100w bulbs on a 6A, that would be 5.65A

 

[Richard Burns]

The resistance of a single 1mm2 copper conductor at 20oC is 19.5 mohm/m (possibly 18.1 in OSG) this gives a volt drop of 6.55 V over 56m at 6A. You may be looking at R1 + R2 values instead which are two conductors in series so your length would then be 112m.

 

[telectrix]

true. i've not got my osg to hand, but in the older version ( 16th,2004, it gives 38m for 1.0/1.0 on a 6A.

 

[stv292]

how do you derive the volt drop from the resistance value's, i was using mV/A/m

 

[Richard Burns]

Yes sorry not thinking what you were using. I did V=IR current is 6A, resistance is (19.5mohm/m*56m) =1.092 ohms so volt drop = 6*1.092 =6.552V

 

[stv292]

that helped a lot, thanks

 

[i=p/u]

and I x R = v

 

[Chr!s]

Yes sorry not thinking what you were using. I did V=IR current is 6A, resistance is (19.5mohm/m*56m) =1.092 ohms so volt drop = 6*1.092 =6.552V

And what about the volt drop in the neutral ?

Regards Chris

 

[Chr!s]

hi

the osg say's i can use 56m of cable of 1.0/1.0 installation method 103,101 e.tc. for lighting, on a radial at 6A. the mV/A/m is 44.
so 44x6x56/1000=14.7v that is 6% of lighting not 3%.
what am i missing

Your missing the fact the load is distributed along its length.

Regards Chris

 

[telectrix]

well spotted, that man.

 

[i=p/u]

isit not just in line conductor you work out vd???

 

[Chr!s]

isit not just in line conductor you work out vd???

Does current flow in the neutral ?

Regards Chris

 

[i=p/u]

it does but when you doing the sums , is tha mv/ counting in neutral aswell. u very clever chris or have you been sparking since you 5