Voltage Drop Calculation vs OSG

[Simon47]

The "Loop Length" column shows the cable length from CU to first light switch (P1) and between each light switch thereafter.
I think you are describing the method shown in the Example below.
View attachment 119067

Yes

I did follow this through and as you say the drops appear significantly lower.
I'd dismissed it believing the values couldn't be that far off from the standard forumla used in methods 1 & 2.
Provided I haven't mucked up on the arithmetic, the max Vd is 1.65V (0.72%) which I'm struggling to believe, but happy to be schooled.

View attachment 119068

I haven't checked any numbers, especially working on small phone screen, but the approach looks right.

 

[Watkins88]

Its been an interesting excercise that I think has highlighted its not neccassarily the furthest point you'd find the greatest Vd as some have suggested. In this circuit Vd appears to be at its worst 45m from the CU whereas the furthest point is 51.5m.

The question I suppose I'm asking myself at this point is why isn't it always calculated in this detail?
Is it simply time where the alternative is a playing it safe approach with a quick calculation that could result in either an oversized cable or split circuits.

 

[Rockingit]

I’d need to stick my head in a theory book as a quick refresher but it occurs to me that what’s also missing from this discussion (as, if we’re going to have an actual theory discussion on here for a rare refreshing change then let’s have one…) is that the entire load on this circuit/s is LED and therefore all manner of other aspects come into play (theoretically) as well to affect the energy consumption - inrush and reactance / pf being two obvious ones. Add to that mix some good old fashioned conductor induced voltages from a few 2-way strappers and some smatterings of capacitance and the smoke starts coming out of your ears. The standard circuit maths is otherwise straight forward if not tedious as it’s resistances in parallel for every combination of Sum(lb) radial line (plus the feeders in every combination).

(This ^^ is why we have prescribed tables to use instead, stops the ear smoke thing).

 

[littlespark]

Has it already been mentioned that in some lighting configurations, the line takes a much longer route than the neutral….?
Do you take an average, or the maximum?

Especially long corridors with a couple of 2 ways and any number of intermediates inbetween.


My 2 pennies worth is that the tabulated values have all these thoughts already built into them…

 

[Pretty Mouth]

The question I suppose I'm asking myself at this point is why isn't it always calculated in this detail?

I created a voltage drop spreadsheet for this sort of thing. I used to use it to calculate the drop when designing regular 230V lighting circuits for ordinary houses, but I don't bother anymore. After using it a few times, I concluded that with LED lighting, it's not easy to exceed the 3% allowance, and even if you did go over by a little way, the consequences are negligible.