Voltage Drop Clac on Light Poles

[Nom Deplume]

I am trying to calculate the VD on a string of light poles.

Do I calculate the VD at each pole by using the current at each pole and the distance to the source?

I have six poles that are 100' apart with a 275' home run.
The poles are 600 watts (3amps) each and will be at 240volts.
We will be using #6's for the wiring on 30 amp CB's.

By using this method, I am getting a 2.03% VD at the first pole and 0.95% VD at the last pole.

Is this the correct method to calculate the VD on a circuit that will be dropping load the further you get from the source?

 

[rrc14]

Is it possible for you to draw a sketch and post; I'm having a hard time visualizing what you describe.

 

[bob]

1. From the source to pole use all of the amperage for all lts. VD at Pole #1
2. From pole#1 to pole #2 use amperage total amps from pole 1 to pole 2. Add this VD to VD at pole#1
3 From pole #2 to pole #3 use total amps from pole #2 to pole #3. Add this VD to VD at pole #2
same for pole 3 to pole4. same for pole 4 to pole 5, same for pole 5 to pole 6.

 

[iwire]

I have six poles that are 100' apart with a 275' home run.
The poles are 600 watts (3amps) each and will be at 240volts.
We will be using #6's for the wiring on 30 amp CB's.

I would figure it as Bob has explained.

A couple of things I will add, you may find reducing conductor size as the circuit progresses might save money although it is more complicated. For instance a 4 AWG home run with 8AWG from there to the third pole and 10 AWG for the last three.

Another thing is the size of the EGC will have to increase as well per 250.122(B).

 

[lielec11]

By using this method, I am getting a 2.03% VD at the first pole and 0.95% VD at the last pole.

Where is your "%" in reference to? I would assume the voltage drop would be worst at the further pole, and least at the closet pole.

For example...

If at pole #1 the VD is 1 volt, that would be your starting voltage for poles 2-6. It is impossible for the voltage drop at pole 6 to be less than that of pole 1.

 

[GoldDigger]

1. From the source to pole use all of the amperage for all lts. VD at Pole #1
2. From pole#1 to pole #2 use amperage total amps from pole 1 to pole 2. Add this VD to VD at pole#1
3 From pole #2 to pole #3 use total amps from pole #2 to pole #3. Add this VD to VD at pole #2
same for pole 3 to pole4. same for pole 4 to pole 5, same for pole 5 to pole 6.

FWIW, and not going to make a practical difference, make sure that you are adding the voltage drops rather than the percentage voltage drops as you work your way out the chain from the source.
Also critical here is that for the each segment the current to be used is the total current drawn by all of the poles that are not upstream of the point in question.
You do not add the VD for each of the pole currents, you add the currents and calculate the VD at that point.
It all sounds simple, but it is easy to write down the math wrong.

 

[Nom Deplume]

Would the calculations work if I did them this way. This is only an example so the math will not be correct.

240 volt source and 3 amps per pole.

Pole 1, 240 volt and 18 amps=VD of 2 volts=238 at pole 1
Pole 2, 238 volts and 15 amps=VD of 2 volts=236 at pole 2
Pole 3, 236 volt and 12 amps=VD of 2 volts=234 at pole 3
Pole 4, 234 volts and 9 amps=VD of 2 volts=232 at pole 4
Pole 5, 232 volts and 6 amps=VD of 2 volts=230 at pole 5
Pole 6, 230 volts and 3 amps=VD of 2 volt=228 at pole 6

 

[Nom Deplume]

Does voltage drop even mater if the LED drives can accept a range of voltage input from 120-277?

 

[GoldDigger]

That is exactly how I would do it.
With real numbers the added voltage drop will get smaller in proportion to the current as you go out.
Distance to first pole might also be different from distance between poles.

 

[GoldDigger]

Does voltage drop even mater if the LED drives can accept a range of voltage input from 120-277?

As practical matter, probably not although the lost power might be a concern for a really long run....

 

[BAHTAH]

Volt Drop Calc on Light Poles

Volt Drop Calc on Light Poles

I figured 275ft to the first pole and 100ft between all the poles, 3amps at each pole.
Using the Load-Center-Length method and #6 -CU would be a VD of 3.87% at 240V Single-Phase or 3.35% Three-phase.

 

[jrohe]

I am trying to calculate the VD on a string of light poles.

Do I calculate the VD at each pole by using the current at each pole and the distance to the source?

I have six poles that are 100' apart with a 275' home run.
The poles are 600 watts (3amps) each and will be at 240volts.
We will be using #6's for the wiring on 30 amp CB's.

By using this method, I am getting a 2.03% VD at the first pole and 0.95% VD at the last pole.

Is this the correct method to calculate the VD on a circuit that will be dropping load the further you get from the source?

Assuming you want to limit voltage drop to 3 percent, the total number of volts you can drop on the circuit would be 240 * .03 = 7.2 volts.

With this in mind, assuming copper wire, the six segments of wire should be:

Segment 1 (18 amps at 275 feet): #4 AWG (3.060 volts dropped on segment)
Segment 2 (15 amps at 100 feet): #4 AWG (0.927 volts dropped on segment)
Segment 3 (12 amps at 100 feet): #6 AWG (1.180 volts dropped on segment)
Segment 4 (9 amps at 100 feet): #6 AWG (0.885 volts dropped on segment)
Segment 5 (6 amps at 100 feet): #6 AWG (0.590 volts dropped on segment)
Segment 6 (3 amps at 100 feet): #8 AWG (0.469 volts dropped on segment)

Total volts dropped on circuit = 7.11 volts (2.9625%)

 

[Iron_Ben]

Your basic approach, realizing that the current drops off after each pole and calculating accordingly, is good. A couple of things:

You mention 277. When I worked for the POCO we surely used 277 when available. That much less voltage drop, smaller conductors, etc.

Don't forget to account for the voltage drop up the pole. Luminaire mounting height might be 20 feet, might be 75 feet (ballfield), I don't know. And often times that is only two #12's.

But against that, check what the lights (ballasts) will accept on the low end. I used to see -10% as the lower limit pretty often. Very generous, and I would not want to flirt too closely with only supplying 108 or 216 volts, but good to know.

Ben


Sent from my iPhone using Tapatalk

 

[Nom Deplume]

Now since this is a 0-10volt dimming control, what size wire should I use? The driver load is 450ma per head. 2 heads per pole. 6 poles per circuit.
Does the cable need to be twisted sheild or individual conductors?
Will the fact that the power and control conduit is in the same trench next to each other for the entire length have any affect on the signal.