Voltage Drop

[resistance]

Has anyone every ran an underground cable 300 feet or more from a source--to serve a 120v [non-low voltage] lighting load [example of loads being served: 8 post light]. If so, did you take VD in consideration per NEC recommendations. If so, why? Just some information: I have a customer that has 8 post lights around their yard that never had wiring ran to them (customer hired an electrician on the side, that left a couple loose ends--an in total, they will need up to 6oo feet of underground cable. I plan to split the lighting--making it 300 feet per run. Yet, i'm not going to go with the NEC's recommendation of 3%, yet I will be running a #10 copper to complete this install.

 

[iMuse97]

Has anyone every ran an underground cable 300 feet or more from a source--to serve a 120v [non-low voltage] lighting load [example of loads being served: 8 post light]. If so, did you take VD in consideration per NEC recommendations. If so, why? Just some information: I have a customer that has 8 post lights around their yard that never had wiring ran to them (customer hired an electrician on the side, that left a couple loose ends--an in total, they will need up to 6oo feet of underground cable. I plan to split the lighting--making it 300 feet per run. Yet, i'm not going to go with the NEC's recommendation of 3%, yet I will be running a #10 copper to complete this install.

I ran some post lights on a commercial property and certainly did take that VD 3% as my guide. While the fixtures as installed were 120v incandescent, I was asked to account for the fact that they may run other lighting from these poles, such as Christmas lights, or may at some point change the fixtures to HID type luminaires. My total length of run was closer to the 600 feet you first mentioned.

The reason, then, that I took voltage drop into consideration, was primarily because I consulted with the customer and they were willing to pay for the extra wire to achieve the desired result. I pointed out to them that the voltage drop increased with the increased load, and light output diminishes quickly after a certain point.

If the conduit or trench is big enough, #8 wire doesn't cost that much more than #10, IMHO. I'd suggest it to the customer, if you think it's an issue they need to know about, or just install it, as a quality job, and bill accordingly.

 

[ActionDave]

Just my opinion, no math involved, I think you are fine with 10's for this application.

 

[iwire]

Has anyone every ran an underground cable 300 feet or more from a source--to serve a 120v [non-low voltage] lighting load [example of loads being served: 8 post light]. If so, did you take VD in consideration per NEC recommendations. If so, why?

Of course we have.

Why? because it is the professional and right thing to do. (and many times that is what the prints require)

We have run 4 AWG copper to serve 120 volt 15 amp receptacles on a roof. (Large building)

We almost never use anything as small as 10 for underground circuits to outdoor lighting.

 

[resistance]

@iwire:
Not too many residential homes (non-farm land) requiring that long a lighting run--at least not in my area.

@Imuse:
#8 is the idea way to go, but the customer will need more persuasion.

 

[resistance]

Update: After giving the customer all my calculations (they had other things done, that required very long runs), they agreed, and I decided on a number 2 Alum for the outdoor lighting. Of course I had to do some different runs (and modifications) at each post light, but everything worked-out good!

 

[kwired]

Use of MWBC could be helpful in keeping conductor size smaller. You want to try to balance the circuit as much as possible and then you essentially have a 240 volt circuit instead of 120 volt, more voltage = less voltage drop on same sized conductor.

For conductors that are buried and there will be a lot of expense to bury new ones it is worth considering if you can step up voltage and possibly keep existing conductors. Cost of transformer(s) often is not worth it on the initial install when you could have just used larger conductors to start with.