Single phase vs 3 phase lighting circuit

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mbrooke

mbrooke

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Say you had to wire over several hundred LEDs on a sales floor. Would you run several 3 phase circuits (14/3) or many single phase circuits (14/2)? Which would be your pick?
 
mbrooke said:
Say you had to wire over several hundred LEDs on a sales floor. Would you run several 3 phase circuits (14/3) or many single phase circuits (14/2)? Which would be your pick?
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First, I'd use fewer 20a circuits. Second, you'd need 12-4 to supply three phases to a neutral. 3-conductor only gets you two circuits. You are using MC and not NM (presuming suspended ceilings), right?

Which way to go also depends on the "geography" of the cabling layout and the switching arrangement. It may pay to use multi-conductor cable from the panel to the switches, and 2-conductor from there.

Added: We're really only talking about the home runs anyway. Generally, I prefer multi-conductor to minimize filling of the bus terminals. Of course, this route now requires multi-pole breakers in many places.

Between the cost of multiple-conductor cables compared to bulk rolls of 2-conductor, and the extra cost of multi-pole breakers, it may not pay. Of course, handle ties are permissible, but not easy to find in all brands.
 
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LarryFine said:
First, I'd use fewer 20a circuits. Second, you'd need 12-4 to supply three phases to a neutral. 3-conductor only gets you two circuits. You are using MC and not NM (presuming suspended ceilings), right?
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208 volts on 120-277 drivers, so 3 conductors would give 3 circuits.

Suspended ceiling, MC cable.


Which way to go also depends on the "geography" of the cabling layout and the switching arrangement. It may pay to use multi-conductor cable from the panel to the switches, and 2-conductor from there.

Added: We're really only talking about the home runs anyway. Generally, I prefer multi-conductor to minimize filling of the bus terminals. Of course, this route now requires multi-pole breakers in many places.

Between the cost of multiple-conductor cables compared to bulk rolls of 2-conductor, and the extra cost of multi-pole breakers, it may not pay. Of course, handle ties are permissible, but not easy to find in all brands.
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This what I've was looking for :D



I'm thinking both the home runs and the switches/contactors there after.


Can't seem to find which is more economical.
 
mbrooke said:
208 volts on 120-277 drivers, so 3 conductors would give 3 circuits.
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So, you'd be using a delta configuration. A little unorthodox, but not unheard of. Will require 2-pole breakers likely require multi-pole switching, too.

Can't seem to find which is more economical.
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Lay out a sample run of each method, i.e., a group of three circuits, and price the differences:

The cost of 3000 ft of 2-conductor vs 1000 ft of 3-conductor.
Three 2-pole breakers vs one 3-pole; also affects panel spaces.
Three 2-pole contactors vs one 3-pole; depends on switching flexibility.
Labor of pulling and hanging three cables vs one; depends on layout.
Connectors and other hardware; how many KOs will you need, and have?

That kinda stuff.

You may be better with a nipple from the panel to a "break-out" box above.
 
LarryFine said:
So, you'd be using a delta configuration. A little unorthodox, but not unheard of. Will require 2-pole breakers likely require multi-pole switching, too.
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Yup delta configuration- more watts from 12/2, one less wire using 12/3.

The 3 phase option will need a 3 pole switch if extending the 3 phase circuit to the lights.


Lay out a sample run of each method, i.e., a group of three circuits, and price the differences:

The cost of 3000 ft of 2-conductor vs 1000 ft of 3-conductor.
Three 2-pole breakers vs one 3-pole; also affects panel spaces.
Three 2-pole contactors vs one 3-pole; depends on switching flexibility.
Labor of pulling and hanging three cables vs one; depends on layout.
Connectors and other hardware; how many KOs will you need, and have?

That kinda stuff.

You may be better with a nipple from the panel to a "break-out" box above.
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All good ideas. :)

Any idea on about box fill on recessed LEDs?
 
mbrooke said:
All good ideas. :)
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I do that sometimes. ;)

Any idea on about box fill on recessed LEDs?
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Depends on the J-box, but I usually opt for 1ph runs vs 3ph runs. I wouldn't want to have to make any extra connections.

But the, you're using line-to-line connections, so there will be fewer extra connections to have to make for the feed-throughs.
 
LarryFine said:
I do that sometimes. ;)


Depends on the J-box, but I usually opt for 1ph runs vs 3ph runs. I wouldn't want to have to make any extra connections.

But the, you're using line-to-line connections, so there will be fewer extra connections to have to make for the feed-throughs.
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And this is the paradox keeping up this night. :happyyes::p
 
mbrooke said:
And this is the paradox keeping up this night. :happyyes::p
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Don't forget to calculate how much power (va) you'll be able to deliver per dollar each way, too.

1ph wiring, where 3ph is practicable, is starting to look more expensive; and redundant.
 
LarryFine said:
Don't forget to calculate how much power (va) you'll be able to deliver per dollar each way, too.

1ph wiring, where 3ph is practicable, is starting to look more expensive; and redundant.
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3 phase = 7,200 va for a 44 buck breaker

1 phase = 4,160 va for a 10 buck breaker or 12,480 for 3 breaker 30 bucks

2 3 phase = 14,400 va for 88 bucks


Single phase is looking cheaper- but

12/3 MC 1000 feet $755

12/3 MC 1000 feet x 2 = $1510

12/2 MC 1000 feet $460 x 3 = $1380

Switch

3 phase = $29

3 phase x 2 = $58

1 pole switch $4.49 x 3 = $13.47


Labor how ever will make the 3 phase option a lot cheaper - I think. And the panel cleaner.
 
Many considerations mentioned are ones that maybe keep installation cost down.

Something else to consider is how much of the lighting is down when you turn off a circuit or when one fails (maybe a ground fault).

If you can get entire floor on one MWBC, you still may not want one problem to leave you in total darkness.
 
mbrooke said:
3 phase = 7,200 va for a 44 buck breaker

1 phase = 4,160 va for a 10 buck breaker or 12,480 for 3 breaker 30 bucks
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That's 2400 va for a 120V/20A circuit. The power you can get out of 3 bus positions with 20A breakers is going to be the same either way.

Cheers, Wayne
 
LarryFine said:
And that's why we use the 1.73 number.
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1.73 is rounded off, the two calculations were only 4 VA different, had square root of 3 been rounded off to more decimal places the end result should get even closer.

Only thing square root of 3 comes into play for is to calculate new current where it divides into the multiple paths of the three phase system, otherwise the VA is still the same whether it is supplied by single or three phase source.
 
kwired said:
1.73 is rounded off, the two calculations were only 4 VA different, had square root of 3 been rounded off to more decimal places the end result should get even closer.

Only thing square root of 3 comes into play for is to calculate new current where it divides into the multiple paths of the three phase system, otherwise the VA is still the same whether it is supplied by single or three phase source.
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Honestly, its my mistake for not rounding 7196 to 7,200 va.
 
I would consider 15 amp circuits. I've been going that route lately because it's just easier and quicker to work with and the junction boxes on a lot of the fixtures I've had to install are quite small. For some reason, 14/2 mc is about the same cost as 12/2, but I still think it's worth it.
 
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