Voltage drop calcs

[Cider]

Hi

Could someone kindly put me in the right direction for voltage drop in cables.
I have the formula from OSG (mV/A/m) x lbxL divide 1000 but cant get my brain to kick in and piece everything together.
There is very little in 7671 unless im looking in the wrong part.
Do I require tables for the cables.
Many thanks

Cider

 

[Amp David]

Think the tables you're after are in GN3, but you can also find table on the manufacturers websites

 

[Cider]

Thanks, how do i get hold of GN3?

 

[malcolmsanford]

Appendix 4 of the BS 7671-2008 page 257 section 6 deals with volt drop. In fact if your designing circuits then appendix 4 as a whole is a good thing to become familiar with

 

[telectrix]

volt drop for a given csa of cable is given in app.4 brb. and is in millivolts per amp per metre. so you have to multriply the value from brb by the current, then the length. then as it's given in millivolts, divide bt 1000 to get volts.

 

[Cider]

Thanks all. You guys sure know 7671 well.


Telectrix, brb ?

 

[telectrix]

big red book, otherwise known as BS7671, the bible, bed time reading for electro fanatics, cash cow for the IET

 

[Sparky Ninja]

Cider are you doing a cable calculation or an assessment of an existing?

 

[ian.settle1]

big red book, otherwise known as BS7671, the bible, bed time reading for electro fanatics, cash cow for the IET

Soon to become the BGB - Big Green Book

 

[Cider]

Cider are you doing a cable calculation or an assessment of an existing?

assessment

 

[Sparky Ninja]

assessment

Assessment of existing is done with the formula..

vd = (R1&RN) x Ib x F

where F=1.20

 

[Chr!s]

Assessment of existing is done with the formula..

vd = (R1&RN) x Ib x F

where F=1.20

Just a point, if using Appendix 4, then the assumed temp will be at 70 C/90 C, so no factor required unless adjustments for temp are being made.

Onsite Guide, the Resistances are taken at 20 C, so as Widdler has pointed out correction factor will be required to get from lets say 20 C to 70 C.

Chris

 

[Sparky Ninja]

The factor is used if no other information is known.

 

[i=p/u]

IxR=V, walla