Parking Lot VD

[Al Pike]

I have 11(240v,400w) lights coming to a hand hole at 400' from the panel. One group has 5 lts and the other has 6. The question is how do I figure VD after the hand hole splice.I figured #4 to carry the entire load at the 400' splice,but i don't know how to figure the other two 300' runs. If the lights were in line I would'nt have a problem, but being I'm going two different directions with different amps, I'm not sure how to do the math. I know its less but I dont know how it relates to the original VD. I'm thinking the #4 is to small for 1ph and I might have to figure 3ph? Am I way off on this?
Thanks.

400' splice VD=2*k*i*l/cm 2*12.9*20*400/41740 = 4.9v at 2%

 

[kingpb]

You can turn this into a real calculation nightmare or you can simplify.

I like to simplify, but that's maybe more expensive to install.

Calculating amps = 400W/240V = 1.667A ea
11 fixtures = 18.4A. Divide by 0.85 power factor and I'll use 22A (nice round number plus it will go on a 30A 2-pole breaker) That would be 12A for 6 fixtures and 10A for 5; you need to use actual fixture data to get correct amps.

With 6 lights on one tap, and the 5 on the other, use the 6 lights at a total distance of 700ft. That works out to a #4 copper, minimum. Now what size is needed for the full 22A going 400', also requires #4 copper.

The 5 lights going the other way, full 700' only requires a #6 copper, so you could decrease wire size from the tap box, but for simplicity I would use all #4 and be done with it.

 

[Al Pike]

That's the way to do it. I wish I would have thought of that. Sometimes you have to take a break and ask for help. You saved my day Thanks so much KingPB

 

[Al Pike]

Another thought,could I figure out the VD for the 700' and then take the remaining 300'

2*12.9*9.8*300/16510=4.68

4.68/240=1.9vd? and use#8

 

[Al Pike]

I guess what I'm asking is, can the branch taps to the next set of lights be figured off 300' being that the entire load was figured at 400' to the hand hole?

 

[kingpb]

I think what your asking is can you do it in segments?

You can take the full load from the panel to the tap point, 400'.

Then take your 6 light light load from the tap point to the farthest light, 300'.

Using a program I come up with a VD of around 2.3% to the tap point using #4. From the tap point to the 300' 6th light I get another 1.45% using #6. Total is 3.75%.

Probably good enough since your figuring the tap load all the way out 300' which would not be the real operating case.

But now your putting much more effort into it

 

[Al Pike]

Thanks again but I have no choice other than to segment correctly. I under bid due to my errors and I'm correcting and trying to save where I can. I also just found out that the voltage is 208 so I resized my branch ckt to #3. My next issue is the current at 2.3*11=25.3 *125%=31.6a needing a 35a breaker.
Question:I planed on running #10 up the pole,but do I need in line fuses in the base or can these be considered a tap.
I'm learning the hard way but I will survive and be better for it.
Thanks

 

[kingpb]

If your trying to save every way possible, then do each segment individually. The calcs are just longer but fairly straigt forward. Just use the current in each segment to find VD for that segment, then the simply add together back to the panel.
I like to start at the end and add current as I go, but you can go the other way and subtract. You maybe able to drop another size as the load reduces out toward the end of your circuit.

Might want to price it using aluminum as well, much cheaper. The inline fuses are probably going to be necessary since the pole height itself is going to require longer than 10' or even 25'. You'll need to look at the NEC on that.

 

[topgone]

. . . . .you need to use actual fixture data to get correct amps.

This is a very important thing to do when trying to calcualte VDs! My experience tells me a 400W/240V metal halide (together with its start ballast,etc) draws around 2 amps ea!