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Posted By: kyelectric 120vs240 lighting - 01/05/07 11:47 PM
What is the advantage of using 240v single phase lighting vs. 120v lighting. The wattage is still the same if you use P=IE. On the 240v circuit, the voltage is higher and the current is lower. But, you are still limited to 2000 watts on a 20 amp breaker and 1500 watts on a 15 amp breaker. So you really haven't gained anything. Is there any advantage that I am missing? I am involved in a job where 10 400 watt metal halide lights are going to be hung and we are trying to decide on what voltage to use. Thanks!
Posted By: Dnkldorf Re: 120vs240 lighting - 01/05/07 11:49 PM
Higher currents=Higher line losses.
Posted By: iwire Re: 120vs240 lighting - 01/05/07 11:52 PM
The short answer is always use the highest available voltage.

If the choice is between 120 or 240 using 240 will allow twice as many fixtures on one circuit.
Posted By: ElJay Re: 120vs240 lighting - 01/05/07 11:53 PM
The higher the voltage the more efficient the lights will be.
Posted By: iwire Re: 120vs240 lighting - 01/05/07 11:57 PM
Quote
On the 240v circuit, the voltage is higher and the current is lower. But, you are still limited to 2000 watts on a 20 amp breaker and 1500 watts on a 15 amp breaker.

Wait a minute.

240 x 20 = 4800 watts

120 x 20 = 2400 watts

Hit it with the 80% for continuous load and your looking at 3840 or 1920 watts.
Posted By: ShockMe77 Re: 120vs240 lighting - 01/06/07 12:06 AM
Plus, if you're doing parking lot lights where the distance of the wire comes into pay, you'll need to consider voltage drop. One way to combat this is by using a higher voltage.

Good discussion here.
Posted By: HotLine1 Re: 120vs240 lighting - 01/06/07 12:16 AM
OK, Bob caught the math error.

And I MUST say, Ron, you were in class, and paid attention. Good man!!!

10-400 watt MH, with avg ballast loss is approx. 4600 watts. kind of tough to get it on 1 circuit. It's over a tad at 277, would be good at 480, but based on Ky's post he has 120-240 only

John
Posted By: ShockMe77 Re: 120vs240 lighting - 01/06/07 12:29 AM
Off-topic, sorry...

You taught us well, John. I impressed a customer of mine the other day by showing him how much he was paying for the lights I installed in his back yard using the technique you taught me. It goes without saying (but I will anyway) that the customer was impressed.
Posted By: HotLine1 Re: 120vs240 lighting - 01/06/07 01:15 AM
Ron:
Thank you for the compliment; and thank you for using something from the course.

John
Posted By: Scott35 Re: 120vs240 lighting - 01/06/07 01:32 AM
While the higher Voltages are desired in Lighting Circuitry designing - primarily due to the fact that Lighting Circuits are LOOOOOOONNNNGGGG Distances and lengths,
There are a few things to consider first:

<OL TYPE=1>

[*] Lamp Screwshells having Voltage to Ground,


[*] Running Lighting Loads directly from Photocells.
</OL>

Typically, when driving Lamps &,or Ballasts from L-L Circuitry, the Lamps' Screwshell will have the System's Voltage to Ground -
unless:

* The System is a Corner Grounded Delta, and the Grounded Conductor is used as "Common" to the Lighting Fixtures,

or

* The System is an Ungrounded Delta (then the Voltage to Ground on either side of the Circuit is anyone's guess!!!)

These issues are more along the lines of "Typical Design Issues", but nevertheless are something to ponder.

< Opening Can O' Worms Controversy Per MWBC >

A typical Design strategy I apply when dealing with Parking / Exterior Lighting, and the Project has a 120/240V 1Ø 3 Wire System available, is to design these loads across 3 wire circuits - with the loads as balanced as possible.

Example:
Light Standards (Poles) contain Two Luminaires - each being 250W MH.
2 Circuits to each Pole.

The Voltage Drop on these Circuits will be applied as if the Luminaires are driven at 240 Volts, so it really helps out on long circuit runs.

Each L-N Circuit is designed to carry a maximum of 50% Capacity at 100%, or 1200 VA without LCL (10 Amps).
With an LCL adder, the maximum load values would be 12.5 Amps, or 1500 VA.

The Voltage Drop would "Naturally" be figured at 240 Volts, as long as the loads remain balanced.

So, as a suggestion, you might consider going the Multi Wire Branch Circuit (MWBC) route on these Fixtures.


< Closing Can O' Worms Controversy Per MWBC >

Adding more things to think of!

Scott35
Posted By: kyelectric Re: 120vs240 lighting - 01/06/07 01:48 PM
iwire, thanks for catching the math error. I was only thinking single pole breaker. But with the 20 amp double pole breaker you can run up to 3840 watts. So all of these replies have helped me determine that using the higher voltage will decrease line losses, increase efficiency, keep voltage drop to a minimun and allow more of the light fixtures on one circuit. Can I run #10 copper and install a 30 amp double pole breaker and put them all one one circuit? Thanks for all the replies!
Posted By: Rewired Re: 120vs240 lighting - 01/06/07 02:15 PM
Off topic a little but why put them all one one circuit??? If that circuit faults out and trips the breaker, you are in total darkness..... Just something to think about...

A.D
Posted By: ShockMe77 Re: 120vs240 lighting - 01/06/07 08:20 PM
^^
I agree. Do at least 2 circuits in case one is having a problem. That's a great design idea.

In any case, if this run to any of the MH lights is over 200' I would suggest using #10 THWN on a 20A circuit breaker. Just because 240 volts is twice the voltage of 120 doesn't necessarily mean that there'll be less voltage drop. It's all dependant upon the size and length of the conductor and there is more resistance in a #12 wire than a #10.
Posted By: iwire Re: 120vs240 lighting - 01/07/07 12:13 AM
Quote
Just because 240 volts is twice the voltage of 120 doesn't necessarily mean that there'll be less voltage drop.

The drop in volts will be the same for the same load and wire size.

The drop as a percentage of the whole will be half as much with 240.
Posted By: ShockMe77 Re: 120vs240 lighting - 01/07/07 02:19 AM
Thanks iwire!


So using a higher voltage is more effecient.
Posted By: RODALCO Re: 120vs240 lighting - 01/07/07 04:53 AM
The higher voltage will certainly be the better option for metal halides.

Also put the circuit at least over two or more section fuses, mcb's in case of a cable fault, so at least you can keep half or part of the lights going.

Now these days when streetlights or parking lights are not working, people and councils make a big issue about it because of safety, tagging, unlawfull damage etc.

If you use incandescent lights usually a lower voltage (110 or 24) is better because filament lamps tend to have thicker filaments and last longer. ( for streetlights this is rarely used now these days ).
Posted By: pauluk Re: 120vs240 lighting - 01/07/07 05:14 PM
Quote
Just because 240 volts is twice the voltage of 120 doesn't necessarily mean that there'll be less voltage drop.

Quote
The drop in volts will be the same for the same load and wire size.
[Linked Image]

If the load (in watts) is the same, the current at 240V will be only half that at 120V. So if the size and length (and hence the resistance) of the wire is the same in each case, the voltage drop must be lower, not only as proportion of the supply voltage but also in absolute terms.
Posted By: iwire Re: 120vs240 lighting - 01/07/07 05:20 PM
Paul you are right and I agree. [Linked Image]

That is why I said "will be the same for the same load"

In other words if the wire size and current remain unchanged the the amount of volts lost will be the same at either voltage but as a percentage it will be less.
Posted By: EV607797 Re: 120vs240 lighting - 01/08/07 05:07 AM
But, on a single-phase service, using 240 volts for any load will keep it balanced. I have never confirmed this, but I was told by an old-timer (a former boss) that typical electric meters register the load on higher-usage leg as what's billable, even if the other leg has less load. If what he said is true, then wiring as many 240 volt circuits as possible will be the most efficient.

He always said "using a neutral is throwing money into the ground". Wonder if he might have been right?
Posted By: iwire Re: 120vs240 lighting - 01/08/07 10:08 AM
No meters do not bill both legs based on the usage of one leg.

You pay for what you use be it 120 or 240.

But the balancing is of course better with 240 loads.
Posted By: Eddy Current Re: 120vs240 lighting - 01/08/07 12:51 PM
Pot grower's myth:
"If I run my lights at 240v it will cost less than at 120v right?"
Posted By: walrus Re: 120vs240 lighting - 01/08/07 03:06 PM
Why is balancing better at 240?? If I run 2 120 v circuits on different phases, how is that any different than a single 240v circuit??
Posted By: EV607797 Re: 120vs240 lighting - 01/08/07 04:25 PM
I had made my statement about meters based upon information I had been told by an old timer many years ago and I never actually confirmed it. He insisted that we always keep our load evenly distributed in the panel, which always makes perfect sense to me. HIS logic however was that if one leg has say, 60 amps running on it and 35 on the other that the meter would register the higher leg and bill that usage. Like I said, I never knew if this was true or if he was pulling my leg. I have just always done this since then.
Posted By: pauluk Re: 120vs240 lighting - 01/08/07 06:40 PM
Bob,

Quote
That is why I said "will be the same for the same load"

In other words if the wire size and current remain unchanged

O.K., I'm with you now. Same load in amperes, not in watts. [Linked Image]
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