Voltage drop

[eds]

Need to feed 4 receptacles on one 20 amp circuit, along with 6 lights (60) watt lamp on a separate circuit. First drop 100' from source, drop a light, 2nd drop 140' from source drop a second light. 3rd drop 340' from source drop a light and receptacle. 4th drop 380' from source, another light and receptacle. 5th 480' from source, another. light and receptacle. 6th is 520 from source, last light and receptacle. One conduit buried. I seem to remember being able to drop wire size as i drop loads. Am I remembering correctly? Utilizing 15 amp load for receptacle 120v.

 

[Strathead]

Simple answer is yes. I encourage you to do an actual complete voltage drop calculation at least once. The formula and programs are available to do this. It isn't easy.

 

[Arester]

Will not be easy. You will need some heavy gauge I think #3 for the most remote outlet to keep VD below 3% (Assuming 20 deg C ambient and wire resistance at 35 Deg C. ) If inrush current is not an issue I suggest using at least 16A since 20 A breaker can carry 16A indefinitely. You can find VD calc software that let you adjust wire resistance for specific operating temperature at https://mc-group.ca/software_downloads.htm (Although it’s free only up to #6 AWG.)

 

[wwhitney]

Need to feed 4 receptacles on one 20 amp circuit, along with 6 lights (60) watt lamp on a separate circuit.

So you can address this circuit by circuit.

For the (6) lights on one circuit, if the loads are all the same, you can just use the _total_ current and the _average_ distance in your voltage drop calculation. So if it's just 0.5A per light, that's 3A total, and I get an average distance of 330'. #12 Cu gives 2.86% voltage drop per Southwire. No upside to complicating things by changing wire size as you go.

For the receptacles on the other circuit, worst case is 15A (as you specified) at the far receptacle. So again, same size wire throughout to handle that case. Now Southwire says #2 Cu to provide 2.37% VD for 15A at 520'.

However, it's worth noting that if you combine them into one circuit, and check 18A at 520' (which is an overestimate, as the 3A for the lights is averaging only 330' away), you get #2 Cu with 2.84% VD. So combining them isn't a problem VD-wise (but could be for control reasons, or to ensure you have a full 20A at the receptacles, etc.)

Cheers, Wayne

 

[LarryFine]

Or you could just start with the last span, say with #10, and go up one size for each span (perhaps two gauges for the 200' span) as you work your way back toward the source.

If you use a 3-wire circuit, the lighting circuit could be made with a smaller gauge, as long as the receptacle line and the shared neutral are sized for the expected receptacle load.

 

[wwhitney]

Or you could just start with the last span, say with #10, and go up one size for each span (perhaps two gauges for the 200' span) as you work your way back toward the source.

Varying size could make sense for the lighting circuit (except #12 is big enough already), but not for the receptacle circuit. Assuming the design is based on plugging a 15A load into any of the 4 receptacles; then the case of plugging it into the farthest receptacle controls the design, and there's no reason to vary conductor size along the run.

Cheers, Wayne

 

[Tulsa Electrician]

Imagine the electrician that opens that panel and goes .
By this I mean the wire sizes on a two pole or the handle tie on the two single poles with different wire guage size or a splices larger conductor to a smaller one attached to the two pole. A home insp would loose his mind as he reaches for his camera salivating to write it up.

I like the multi wire branch circuit as well. Three current carrying in the raceway.
I would like see the break down the OP does which ever way he goes.

Edit, what type of 60 w lighting load