Voltage drop on lighting circuit

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nizak

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I have a question about lighting and voltage drop.

I have home runs of approximately 165 ft to the first switch point,' that feed switches for lighting.

My question is:?

Do I nclude the length of the fixture runs all the way to the last fixture, or just to the switch point?

Do I include the length of the travelers between 3 and 4 way switch points?

I will have 11 amp loads at 120 volt.

I would like to accomplish this with #12 Cu conductors.

Thanks
 
Yes you would include 3 ways and you include the calc to the first light, then another drop to the second light etc. Unless you have a really long run I would just see what the drop is with 11 amps to the last fixture including the 3 ways.
 
Unlike the distance of the home run, where you need to consider twice the length (drop on hot and neutral), some switch run travelers only increase the length of one wire, while a dead end switch leg will count two wires.
FWIW
 
One thing I always consider with voltage drop is the actual voltage you're starting with, and relate that to a conceptualized minimum.

What I mean is that if you were starting with 120 volts, and you have 3% drop, you have a functioning voltage of 116.4 - so in reality, 116.4 is my target

But if you start with a voltage of 123.8 (which is not uncommon) you will drop 6% before you reach 116.4

The bottom line for me is that I don't care about percentages. I care about the actual voltages
 
Another consideration is the one-way length vs. using the full-loop multiplier (either 2 or sqrt3). A lot of commercial applications use MWBC distribution (less since handle ties required) where the neutral current during business hours is typically at or near zero. Calculating only voltage drop to neutral may permit a smaller gauge wire.
 
James L said:
One thing I always consider with voltage drop is the actual voltage you're starting with, and relate that to a conceptualized minimum.

What I mean is that if you were starting with 120 volts, and you have 3% drop, you have a functioning voltage of 116.4 - so in reality, 116.4 is my target

But if you start with a voltage of 123.8 (which is not uncommon) you will drop 6% before you reach 116.4

The bottom line for me is that I don't care about percentages. I care about the actual voltages
Click to expand...
That's a good point, but often times in new construction we do not know the delivered voltage.
 
James L said:
One thing I always consider with voltage drop is the actual voltage you're starting with, and relate that to a conceptualized minimum.

What I mean is that if you were starting with 120 volts, and you have 3% drop, you have a functioning voltage of 116.4 - so in reality, 116.4 is my target

But if you start with a voltage of 123.8 (which is not uncommon) you will drop 6% before you reach 116.4

The bottom line for me is that I don't care about percentages. I care about the actual voltages
Click to expand...

What if you have light load days where voltage is 123.8, and heavy load days where it is only 119.2?

I generally just figure voltage drop as it relates to necessary conductor sizing based on nominal voltage and not worry about such fluctuations unless they are going to be critical to an application.
 
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