Lighting and Voltage Drop

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winnie said:
Several thoughts:

1) The MWBC approach cuts voltage drop but costs redundancy. A single 3 pole circuit now feeds 3 bays of lights, rather than 3 separate single pole circuits each feeding 1 bay. As a design decision if I would use MWBCs I would 'distribute' each MWBC so that loss of one circuit does not kill light to adjacent bays. I might even arrange things so that adjacent lights were not on the same circuit.

2) On this site I learned a clever trick for dealing with voltage drop on long circuits with distributed loads.

Rather than selecting wire size and calculating voltage drop, the approach is to select a target voltage drop and then calculate the 'circular mils' needed to feed each load with that target voltage drop. Then for each stretch of circuit you add up the circular mils required by all the loads fed through that bit of circuit to get the required wire size for all the loads.

You use the voltage drop equation from this page: https://www.mikeholt.com/technnical-voltage-drop-calculations-part-one.php
But swap the CM (circular mil) term and the VD (voltage drop) term
CM = 2 * K * I * D / VD

K is the resistivity constant, here 12.9 circular mil * ohm / feet different values might be needed for lower temperature operation
The above formula is the single phase formula where D is the one way distance, thus the factor of 2

Here is an example:
9 lights in a bay, fed from the center.
Each light draws 1A at 265V
Target voltage drop of 12V
closest light is 300 feet from source, then 40 feet to each additional light
single pole circuit

light 1: 460feet CM= 2 * 12.9 * 1 * 460 / 12 = 989 (This means that you only need a copper cross section of 989 circular mils to feed this single lamp with the target voltage drop)
light 2: 420feet CM= 903
light 3: 380feet CM= 817
light 4: 340feet CM= 731
light 5: 300feet CM= 645
light 6: 340feet CM= 731
light 7: 380feet CM= 817
light 8: 420feet CM= 903
light 9: 460feet CM= 989

All of the lights are fed by the run from the panel to light 5. So that run needs wire size 645 + 2*731 + 2*817 +2*903 + 2*989 = 7525 circular mils
That wire size is bigger than #12 but smaller than #11. You can't buy #11 so you need #10.

The run from light 5 to light 4 carries the current for lights 1-4. So that wire needs to be 989 + 903 + 817 +731 = 3440 circular mils
That wire size is smaller than #14

Based on the above, I would consider using 15A circuits so that I could use 14ga wire. Increase the wire size only from the panel to the center light of a bay, then use 14ga for the rest.

-Jon
Click to expand...

Very interesting way of figuring this.
 
LarryFine said:
That will end up with the greatest amount of voltage drop of all, as well as the greatest material costs.
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Interesting. OK. In the attached photo on my first post, it shows the location of each light. They are color coded. The green circles are lights that will always be ON. The cyan blue colored light will be hanging over pallets of finished product, so they will be on motion sensors. The darker blue colored lights will be acting as emergency lights. They will be ON all the time, but will be backed up by a generator. These 'emergency lights' will be on a separately derived system (different panel, wire, conduit, well-marked, blah, blah). The bays are numbered from left to right 1-15. Not all bays have the same amount of lights. For example, Bay 1 has 8 lights, Bay 2 has 10, Bay 3 has 6, and so on. Using MWBCs here would give me an unbalanced load if I were to run each bay as a circuit (which is my current plan). But, if I assume all lights are ON all the time, and size my wire accordingly, then I shouldn't need to worry about overloading my neutral, correct?
 
Jody Boehs said:
..These 'emergency lights' will be on a separately derived system (different panel, wire, conduit, well-marked, blah, blah)..
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NEC 700.12(A) typically used onboard EM LED's don't need no stinking separate emergency circuit or generator.

Unless of course your holding out on more details.
 
Many of us have felt like an ignoramus without Planning from a seasoned EE, unless we also happen to be licensed Architects, or Engineers, who never acknowledge being wrong.
 
ramsy said:
NEC 700.12(A) typically used onboard EM LED's don't need no stinking separate emergency circuit or generator.

Unless of course your holding out on more details.
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How will they be powered in the event of a power outage? These lights are the same fixture as the rest of the lights in the warehouse. They are not these wall mounted-battery-powered Emergency Lights. They are a 240W LED UFO fixture.
 
Installers usually work with a lighting supplier to source equipment, who vett counterfeit listings, and are compensated for their expertise thru purchasing.

There are emergency-battery backup options for your specified lights on the dark web, founded by Jeff Bezos & others. I can't warranty these UL markings are free from counterfeit, typical with internet suppliers, nor will I endorse such products in the public domain.

However, it would help if you told us what you role is in this project?

Your profile doesn't tell us if you're an engineer, installer, or building owner.
 
ramsy said:
Installers usually work with a lighting supplier to source equipment, who vett counterfeit listings, and are compensated for their expertise thru purchasing.

There are emergency-battery backup options for your specified lights on the dark web, founded by Jeff Bezos & others. I can't warranty these UL markings are free from counterfeit, typical with internet suppliers, nor will I endorse such products in the public domain.

However, it would help if you told us what you role is in this project?

Your profile doesn't tell us if you're an engineer, installer, or building owner.
Click to expand...
I am a 4 year journeyman electrician that will be managing the installation and wiring of these lights. The company I work for owns another plant in which these lights were used to replace all their existing metal halide lights. They love these lights, hence the reason for purchasing more for their new building.
 
First thing is to update your forum profile "Occupation" to something like JW or Journeyman Wireman. That way if licensed rivals, or local inspectors are lurking they can alert you to other local-regulatory requirements.

Next locate lighting supplier(s) with commercial liability policy to examine the Amazon / internet knock-off with nefarious "UL" or "CE" label from China, who can ignore any subpoena to US jurisdictions during claims.

If supplier says, "we can't beet this price", and won't look for original OEM being copied, then move to next supplier. You need supplier with business address in US territory who can sell NRTL listed equipment from their invoice. May be more expensive, but buying from insured-local supplier gets your client's assets off the hook.
 
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