3 phase lighting circuit

[olc]

Is it common to wire three (277V) lighting circuits together to one 3 pole circuit breaker (I guess the three circuits would be run together with the ballast connected to alternating phases)?
If yes and they are electronic ballast should the neutral be three wires or over size? (the above refers to 277V inside fluorescent lighting)

A sort of related question - Is there any reason not to use 480V (one phase) for exterior pole mounted medium base HID lighting?

 

[charlie b]

1. Yes it is common.
2. I would use the same size neutral as the phase conductors. If the load is balanced, then there will be no neutral current. But if by chance all the lights on Phases A and B are turned on, and the lights on Phase C are off, then the neutral will have the same current as Phase A or Phase B. So it should be full sized, but it need not be bigger than the others.
3. No reason. That too is common.

Welcome to the forum.

 

[augie47]

Is it common to wire three (277V) lighting circuits together to one 3 pole circuit breaker (I guess the three circuits would be run together with the ballast connected to alternating phases)? ?

It used to be real common to use a MWBC for 277 volt lighting. Now that the '08 Code requires simultaneous disconnect (handle tie or 3 pole breaker), I see more plans going to individual neutrals and 1 pole breakers.

If yes and they are electronic ballast should the neutral be three wires or over size? (the above refers to 277V inside fluorescent lighting)

The neutral will then be considered a current carrying conductor and on occasion I see them spec'ed to be oversized but rarely.

A sort of related question - Is there any reason not to use 480V (one phase) for exterior pole mounted medium base HID lighting?

No Code reason that I know of. If the system voltage is over 277 volts to ground the fixture height must bee 22 ft or greater.


(Mr. Beck, I was typing as you answered..sorry)

 

[LawnGuyLandSparky]

Just an aside... Aside from requiring larger step-down transformers, I think all the past benefit of 480v distribution for the purpose of hid lighting in large spaces is now a moot point.

When first employed, an entire floor would be a "steno pool" and everything was either on or off... office buildings don't do it that way anymore.

 

[olc]

That was quick.
The question about the oversize neutral is asked because of harmonics due to the electronic ballast. Same answer?

Generally 277V lighting is used becasue the building has 480V and there is no point to step it down for the lighting. Which is basically what LawnGuy says except that transformer size difference is significant. Also it is usually fluorescent.

 

[LarryFine]

The question about the oversize neutral is asked because of harmonics due to the electronic ballast. Same answer?

For me, yes. Remember, if you have balanced circuits, any harmonics will be the only neutral current.

 

[lakee911]

No Code reason that I know of. If the system voltage is over 277 volts to ground the fixture height must bee 22 ft or greater.

How do you figure?

 

[augie47]

how do you figure?

210.6(d)..............

 

[Chamuit]

210.6(d)..............

I don't have a 210.6.d in my code book.

 

[augie47]

210.6(D) is on pg 47 in the '08 Code

 

[olc]

Just for discussion...
In my case the hieght is moot. The 480 is 277 to ground.
I did a job a while ago that was a fairly large site for which the site lighting was all wired 208V. In hind site I think it may have been worth it to step it up to 480/277.
Have you ever used 347V?
I am not even sure I could get a 208X347/600 transformer.

 

[Mike01]

22 feet

22 feet

just a clarification (on my part) 210.6(d) indicates "Circuits exceeding 277 volts, nominal, to ground", that would mean only fixtures with a voltage more than 277V to ground so a fixture with a 480V-1-phase connection would not fall under the 22' requirement because the voltage to ground would be 277 nominal, so a mounting less than 22' is acceptable.l

 

[weressl]

210.6(D) is on pg 47 in the '08 Code

210.6 Branch-Circuit Voltage Limitations.

​

​

​

​

​

...
(D) 600 Volts Between Conductors.​

​

​

​

​

Circuits exceeding 277 volts, nominal, to ground and not exceeding 600 volts, nominal, between conductors shall be permitted to supply the following:
(1) The auxiliary equipment of electric-discharge lamps mounted in permanently installed luminaires where the luminaires are mounted in accordance with one of the following:
a. Not less than a height of 6.7 m (22 ft) on poles or similar structures for the illumination of outdoor areas such as highways, roads, bridges, athletic fields, or parking lots
b. Not less than a height of 5.5 m (18 ft) on other structures such as tunnels

_____________________
The reference of tunnels seem to imply that it is only intended for outdoor installations, yet warehouses, high celing gymnasiums, halls or hangar type large structures should also be able to use this type of lighting.​

Words?