Votage drop in lighting circuits

[welchyboy]

does anyone know how to calculate the v/d of a lighting circuit with a distributed load

,looking at the final circuit table in on site guide and the conventional way does not allow for this

 

[johninlondon1]

The first stage is to determine the current distribution so we would need to know the distances between each load and the current taken by each load. Also would need to know the cable type or voltage drop per metre.

 

[SPECIAL LOCATION]

Voltdrop?

milivolts per Amp per Metre for different conductor sizes are given in Table 6E2.

so if all the load it at the end of a radial circuit its just your total load Amps and the total length and the respective mV/A/m value of the table...

IF you had a radial circuit with three loads along the length..

just break it down into the respective component parts to suss out the total volt drop..

say your circuit had:-

length 'A' then load 'X'

length 'B' then load 'Y'

length 'C' then load 'Z'

volt drop down length 'A' will use current for 'X'+'Y'+'Z'

volt drop down length 'B' will use current for 'Y'+'Z'

volt drop down length 'C' will use 'Z'

then total volt drop would be values calculated down each length 'A'+'B'+'C'.

BUT....

with a distributed lighting circuit.. it may well be waste of time as due to diversity half the lights may not be on anyway!

AND...

on a more general rough calc..

if you had a 6A, 1.5mm lighting circuit on an average domestic installation, that was no longer than 30m..

even if all your load was at the end of it, the volt drop is still only 29x6x30/1000 = 5.2v

so all ok for within the 3% 6.9v limit.

In reality this domestic scenario would be less cuz of distribution and diversity.

What application are you considering Welchyboy?

If its some big long commercial office circuit wots been badly designed you may need to get your calculator out!?

:^O

There are some old threads discussing this.. opcorn

 

[welchyboy]

Yeah thank you got it sussed now, just trying to work out a few design ideas, and was trying to work out the method used in the final circuit table in OSG, all makes perfect sense now!