Site Lighting Wiring

[ElectDesigner]

Say you are designing lighting for a mall parking lot, what I have seen from experience is that designers provide an extra neutral every three circuits - could someone explain this to me

Lets say you power four lighting poles , and let assume each pole requires one circuit - so A.1, A.3, A.5 & A.7 - so how many wires does one require for this? Naturally I would think 4 wires for the hot, one for neutral and one for ground so in total : 4+1+1 = 6 wires right? But what I have seen is that designers provide 4 wires + 2 Neutral + 1 Grd = 7 wires in total. Could someone please explain this to me? Why can all the circuits share one neutral? Is it because of the unbalanced currents?

 

[raider1]

Because a multiwire branch circuit for a 3 phase system is limited to the 3 ungrounded conductors sharing 1 neutral. If you use a 4th ungrounded conductor it would be on the same phase as one of the other ungrounded conductors and the neutral current on those 2 ungrounded conductors would be additive.

Chris

 

[ElectDesigner]

@raider1 - thanks! as soon as I posted, I had realized the neutral current is the vector sum of all the phases - thanks for verifying. So this then means you can have any three ungrounded conductors sharing the same neutral as long as they are all on different phases.

 

[Dennis Alwon]

@raider1 - thanks! as soon as I posted, I had realized the neutral current is the vector sum of all the phases - thanks for verifying. So this then means you can have any three ungrounded conductors sharing the same neutral as long as they are all on different phases.

That is correct.

 

[don_resqcapt19]

...thanks for verifying. So this then means you can have any three ungrounded conductors sharing the same neutral as long as they are all on different phases.

Not exactly. Compliance with 210.4(B) will require that the breakers be next to each other. Electrically you could use circuits 1, 4 and 5 with a single neutral, but there in no way to comply with the simultaneous disconnect rule.

 

[maghazadeh]

Because a multiwire branch circuit for a 3 phase system is limited to the 3 ungrounded conductors sharing 1 neutral. If you use a 4th ungrounded conductor it would be on the same phase as one of the other ungrounded conductors and the neutral current on those 2 ungrounded conductors would be additive.

Chris

THis is true as far as NEC rules concerns, but many specifiers such as you may call for a dedicated neutral per circuit. for parking lot lighting I would rather to use phase to phase voltage (208, 240, 480V) since normally distances are long.

 

[Smart $]

...for parking lot lighting I would rather to use phase to phase voltage (208, 240, 480V) since normally distances are long.

...and powering with a 3? 3-pole 3-wire circuit reduces voltage drop issues by being 15% more efficient compared to 1? 2-pole 2-wire circuits.

 

[maghazadeh]

...and powering with a 3? 3-pole 3-wire circuit reduces voltage drop issues by being 15% more efficient compared to 1? 2-pole 2-wire circuits.

Smart $,
I never seen a 3 phase lighting fixture. Could you post some more information?

 

[Little Bill]

Smart $,
I never seen a 3 phase lighting fixture. Could you post some more information?

I have never seen a 3 ph fixture but I think I saw where someone had posted about one, might have been another forum. However, many lighting panels are 3 ph and some are for the reason Smart $ stated, less voltage drop. Also easier to balance the panels in some cases.

 

[iwire]

Smart $,
I never seen a 3 phase lighting fixture. Could you post some more information?

18 fixtures

6 connected A-B

6 connected A-C

6 connected B-C

 

[iwire]

I have never seen a 3 ph fixture but I think I saw where someone had posted about one, might have been another forum. However, many lighting panels are 3 ph and some are for the reason Smart $ stated, less voltage drop. Also easier to balance the panels in some cases.

We do a ton of large parking lots, very common for the engineer to specify 3 phase 480 volt circuits in the 20 to 50 amp range with each fixture connected to a pair of phases in rotation.

 

[iwire]

THis is true as far as NEC rules concerns, but many specifiers such as you may call for a dedicated neutral per circuit. for parking lot lighting I would rather to use phase to phase voltage (208, 240, 480V) since normally distances are long.

With site lighting typically being all on at the same time and presumably reasonably balanced you could figure your VD based on the L to L voltage not the L to N voltage even though the fixtures are connected L to N.

 

[Smart $]

THis is true as far as NEC rules concerns, but many specifiers such as you may call for a dedicated neutral per circuit. for parking lot lighting I would rather to use phase to phase voltage (208, 240, 480V) since normally distances are long.

With site lighting typically being all on at the same time and presumably reasonably balanced you could figure your VD based on the L to L voltage not the L to N voltage even though the fixtures are connected L to N.

Not with dedicated neutrals.

Being the troublemaker you endearingly called me in another thread , figuring Vd as you suggest may yield a misleading result. Typically not by any great amount, but misleading all the same. How misleading depends on where fixture neutrals tie into the shared neutral.

For example, you have a balanced MWBC powering a multitude of three-head pole lights. You wire poles with each of the three heads on a different phase... essentially no error because the net neutral current for each pole is zero.

On the other hand, you power each pole L-N, rotating phases amongst poles to balance the circuit. For this case you would have neutral current between poles. Everywhere there is current on the neutral will contribute to voltage drop.

 

[maghazadeh]

:lol:

...and powering with a 3? 3-pole 3-wire circuit reduces voltage drop issues by being 15% more efficient compared to 1? 2-pole 2-wire circuits.

Here as Smart $ state "and powering with a 3? 3-pole 3-wire circuit". 3 phase 3-pole, 3-wire Circuit.

Smart $,
I never seen a 3 phase lighting fixture. Could you post some more information?

If I may have your attention. Smart $ Said "3 phase, 3-pole, 3-wire circuit", THen I said,
" I never seen 3 phase ltg. fixture head". I do not consider one ltg. pole with 3- heads = lighting fixtur. To me that is 3-different fixtures on 1 pole.
[QUOTE]iwire
Originally Posted by maghazadeh
Smart $,
I never seen a 3 phase lighting fixture. Could you post some more information?
18 fixtures

6 connected A-B

6 connected A-C

6 connected B-C [/QUOTE]

All above 18 ltg. fixtures are still not 3 phase fixtures.

Originally Posted by Smart $
...and powering with a 3? 3-pole 3-wire circuit reduces voltage drop issues by being 15% more efficient compared to 1? 2-pole 2-wire circuits.

I just thought Smart $ ment that now ltg. fixture are available with 1 ballast which is a 3 phase ballast hook up to phase A, B, and C. now I see you didn't mean that, otherwise, I am aware of 3 phase panels feeding lot lighting and so on.............:roll: :lol::lol:

 

[Smart $]

I am aware of 3 phase panels feeding lot lighting and so on.............:roll: :lol::lol:

Well at least now I know you don't think I meant 3? lights :slaphead:

But it's not just about lighting being fed from a 3? panel.

 

[iwire]

If I may have your attention. Smart $ Said "3 phase, 3-pole, 3-wire circuit", THen I said,
" I never seen 3 phase ltg. fixture head".

Which was really silly of you to say as smart never said there was one.

I do not consider one ltg. pole with 3- heads = lighting fixtur. To me that is 3-different fixtures on 1 pole.

And I did not say it was one fixture, but electrically it is no diffrent than 3 electric resistant heaters in a common box labeled '3 phase'

18 fixtures

6 connected A-B

6 connected A-C

6 connected B-C

All above 18 ltg. fixtures are still not 3 phase fixtures.

Yes, where did anyone indicate otherwise? As a mater of fact the post clearly indicated they where connected to only two phases.

I am aware of 3 phase panels feeding lot lighting and so on.............:roll: :lol::lol:

That is great, but I was taking about 3 phase branch circuits supplying single phase lot lighting and so on.............:roll: :lol::lol:

 

[iwire]

Not with dedicated neutrals.

Did you really just tell me that? :lol:

I apologize if it was not clear I was talking about MWBCs

Being the troublemaker you endearingly called me in another thread

I knew you would survive.

figuring Vd as you suggest may yield a misleading result. Typically not by any great amount, but misleading all the same. How misleading depends on where fixture neutrals tie into the shared neutral.

Again, no kidding.

If you look at my post I say you 'could' figure it L to L. In most cases I don't look at VD calculations like building a watch. IMO in most cases you don't have to be precise, it can be more like horseshoes and hand grenades

For example, you have a balanced MWBC powering a multitude of three-head pole lights. You wire poles with each of the three heads on a different phase... essentially no error because the net neutral current for each pole is zero.

On the other hand, you power each pole L-N, rotating phases amongst poles to balance the circuit. For this case you would have neutral current between poles. Everywhere there is current on the neutral will contribute to voltage drop.

I am touched that you have so much confidence in my understanding of basic circuits and calculations. hmy:

 

[Smart $]

Did you really just tell me that? :lol:

Yep... but mag' did so first. Consider yourself duly notified!!!

I apologize if it was not clear I was talking about MWBCs

Hmmm... gotta love those conditional apologies.

I knew you would survive.

Resilient little b'turd I am. :happyyes:

Again, no kidding.

If you look at my post I say you 'could' figure it L to L.

And I did not say you said otherwise...

...no kidding!!!

In most cases I don't look at VD calculations like building a watch. IMO in most cases you don't have to be precise, it can be more like horseshoes and hand grenades

In most cases, not just yours, the calculation is neither accurate nor precise. The majority prefers to toss grenades... :slaphead:

I am touched that you have so much confidence in my understanding of basic circuits and calculations. hmy:

Oh, darn! ...I was supposed to keep it a secret.

 

[iwire]

In most cases, not just yours, the calculation is neither accurate nor precise. The majority prefers to toss grenades... :slaphead:

Because what they lack in elegance they have in effectiveness. :thumbsup:

 

[George Stolz]

Man, am I confused. If iwire made up all his lights A-B, B-C, and so on, where is the neutral that people keep talking about? I can't see a reason to make this a MWBC at all. :huh: