Voltage Drop

[mck621]

I need assistance on calculating the Voltage Drop for the following circuit to determine the correct wire size.

Voltage is 120V
Each LED light draws 2.5A
Copper wire in PVC conduit.
Total run length is 470'


270' to the first light and then (5) LED lights spaced 50' apart.

Much appreciated
mck621

 

[junkhound]

assuming:
A. this is a 'help the student with her homework questione, and
B. assume the 2.5W is constant power load. Or does the LED ballast draw a CONSTANT 2.5 A?

Draw your circuit, write out the 5 loop equations

Solve the multiple quadratic equations that result.

Or just put the values into LTspice or PSpice and solve.

Or, just stick yer thumb in the air for 2.5Watts, and us 12 Awg = acceptable drop.

 

[junkhound]

Here is an example for 10 AWG for the solution IF each LED is a constant power of 300W (2.5A *120V)

112.7V
111.6V
110.8V
110.3 V
110.0 V

If constant current of 2.5A and not constant power ( a good ballast would provide constant power load), then
113.2V
112.2V
111.5V
111 V
110.7V

This assumes the ballast has a PFC front end.
above using Orcadn 16.2 student version, download free online.
also, referred to student as 'her' so as to not make a gender assumption -- NOT intended to imply only a 'her' would ask this type a question.
General student comment: If you wrote a homework assignment verbatim, tell the prof some crucial real world details were omitted as outlined above. e.g constant power, constant current, PFC, etc.
BTW, IF really constant current, the loop equations become really simple, on can do the voltage drop by simple summation.

 

[junkhound]

One more for the student* IF wire size the only concern, and IF NEC applies and this is not for cargo hold lighting on a C5A or some such.

1. what is minimum allowable nameplate voltage on the LED ballasts?

2. for wire size assuming the simple current summation voltage drop provides voltage higher than ballast nameplate (typically 106V minimum), then 5*2.5 = 12..5 A
80% of 15 = 12 A for 14 AWG, so 12 AWG needed.

*an assumption of student is made as OP is first time poster but, when looking at profile, see OP is listed as 'project manager' with 36 years in the business - perhaps student imagination or truly someone asking such a basic question who has 36 yers experience as an electrician?

 

[mck621]

Thank you.

 

[Phil Corso]

Mck621...

Search MHF archives for "Series Voltage Drop All Inclusive", started by Spraymax !

Regards, Phil Corso

 

[pv_n00b]

I need assistance on calculating the Voltage Drop for the following circuit to determine the correct wire size.

Voltage is 120V
Each LED light draws 2.5A
Copper wire in PVC conduit.
Total run length is 470'


270' to the first light and then (5) LED lights spaced 50' apart.

Much appreciated
mck621

This is a simple problem and in your profile you say you have been an electrician for 36 years. That's a little confusing.

Treat the circuit as having 6 sections, find the total current for each section by summing up the LEDs fed by that section and the ones that come after, each section will have a voltage drop that is the sum of the previous section's VD plus the current sections voltage drop. I would just set it up in excel and use conductor resistance/ft as a variable and change it to get the VD that was acceptable and choose a conductor with the next lower resistance/ft.