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480V Light fixtures

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A

Allegiantelectrical

Member
Location
Menifee
Occupation
Contractor
Currently quoting a job installing 8 light poles with (12) 150W light fixtures on each pole.

The runs will be fed from two different 480V sources. (4 light poles on one panel and 4 light poles on the other panel)

Just wanting to double check my load calc & conduit fill.

1. Am I right to assume 150W x 12 = 1800W/ 480V = 3.75A at each light pole? If so that means 15A total current on that circuit.

2. With a distance to the furthest pole at 1353’ I should run 4AWG.

3. (5) 4AWG in schedule 40 PVC means I should run 1 1/4” conduit?

4. With a load of 3.75 A at each pole I could run #12 or #10 up each light pole?

Thanks in advance!
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Allegiantelectrical said:
Waiting on the spec sheet for them, but let’s assume they are LED, And let’s assume they do have a driver.
Click to expand...
The you'll need to recheck your calculations using the input current of each driver not the output of the lights. Since these are 480 are you running 3 phase and tapping off of two legs?
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Allegiantelectrical said:
1. Am I right to assume 150W x 12 = 1800W/ 480V = 3.75A at each light pole? If so that means 15A total current on that circuit.
Click to expand...
That looks right, especially if you run all three phases up each pole, which I would.

Allegiantelectrical said:
2. With a distance to the furthest pole at 1353’ I should run 4AWG.
Click to expand...
I would stagger: #4 to the 1st pole, #6 to the 2nd, #8 to the 3rd, and #10 to the 4th.

Allegiantelectrical said:
3. (5) 4AWG in schedule 40 PVC means I should run 1 1/4” conduit?
Click to expand...
That's compliant; you may want 1.5" if the home run is a twisty pathway.

If you stagger the wire sizes, you can also cascade the conduit sizes.

Allegiantelectrical said:
4. With a load of 3.75 A at each pole I could run #12 or #10 up each light pole?
Click to expand...
#12 for sure. You could easily use #14 if your OCPD was low enough.
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I didn't do the math, and I guessed about the wire count.

To me, with L-L loads, running 3ph makes much more sense.

It appears that everything is divisible by 3, even each pole.

3 circuits on 3 wires is better than 2 circuits on 4 wires.
 
W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Allegiantelectrical said:
2. With a distance to the furthest pole at 1353’ I should run 4AWG.
Click to expand...
Quick comment on this aspect: once you figure out your load current (if each pole takes a single 480V 2-wire circuit, and 1800W is the electrical input power, with a 0.95 power factor the current is approximately 1800W/480V/0.95 =4A), if you have multiple such loads on the same circuit, you can use the average distance to each pole to calculate the end-of line voltage drop, assuming constant current loads (which they are not).

For example, if one 2-wire circuit supplies 4A loads at say 247', 600', 1000', and 1353' from the supply, then the average distance is 800', and the total load is 16A. The Southwire Voltage Drop calculator (using the default 0.9 power factor, as it only has single digit resolution, plus that feature is broken on the calculator) say 16A @ 800' on a 480V 2-wire circuit will drop 2.48% (11.9V) with #6 Cu. While your load is spread out compared to just lumping it at 800', the final answer for voltage drop at the farthest load will be the same.

In reality the loads likely behave more like constant power loads, so the farther loads with a lower voltage due to voltage drop will draw more current, so this is not accurate. But it is more accurate that assuming a 16A load at 1353' from the source.

Cheers, Wayne
 
Last edited:
A

Allegiantelectrical

Member
Location
Menifee
Occupation
Contractor
So thank you for all the responses.

I got the specs and it shows 300W light fixture 480V.
I have (2) homeruns with (4) poles on each homerun, (8) lights on each pole

Run 1
Power factor is 0.95
Is 1400' From Gear to furthest light.
I have 300W x 8 lights = 2,400W
2400W x 4 poles = 9,600W
9,600W/480V = 20A
Sizing the overcurrent protective device at 125% means i need a 480V 25A 3-pole breaker
So on run 1 using voltage drop calculator I have (4) 3AWG CU wires. 3-phase conductors & a ground.
I can use 1 1/4" Conduit

Run 2
Power Factor is 0.95
Is 930' from Gear to furthest light.
I have 300W x 8 lights = 2,400W
2400W x 4 poles = 9,600W
9,600W/480V = 20A
Sizing the overcurrent protective device at 125% means i need a 480V 25A 3-pole breaker
So on run 1 using voltage drop calculator I have (4) 4AWG CU wires. 3-phase conductors & a ground.
I can use 1" Conduit

1. Need someone to double check my math on this.
2. Over-current protective device look right?
3. Wire size look right?

This being said how do i connect to the fixtures as 480V 3-phase? I'm used to 277V with single phase conductor, neutral and ground.

Appreciate everyones input!
 
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