Dumb question of the day: Streetlighting Voltage

[DavePayne]

I've been doing electrical design for quite some time but I have never done any streetlighting until now.

The City standards that I'm using suggest that 240v lighting can be used instead of 120v if voltage drop is a issue. Well, voltage drop is an issue but I must confess I don't know what 240v lighting is.

I always thought for that for any fixture (in this case 400W HPS) you needed to connect line-to-neutral. Am I wrong?

For 240v fixtures on a 120/240v system are the fixtures connected line-to-line with no neutral pulled at all? I didn't think this was possible.

Maybe I'm completely out to lunch on this and the standards are referring to a 240/416v system, but I don't think so.

I notice most street light fixtures are available in 240v so maybe this is a common thing.

Any help or advice on this is greatly appreciated.

Dave.

 

[peter d]

Re: Dumb question of the day: Streetlighting Voltage

To quote the often used cliche: "The only dumb question is the one not asked"

It is indeed quite possible, and quite common to use 240 volts for outdoor lighting. Yes, the fixtures are connected line-to-line and the neutral is not required. The third required wire would be the equipment ground.

The 240/415 is a British voltage standard and not used in the U.S.

For reference, the line to neutral voltages are 120 and 277, and the line to line voltages are 208, 240 and 480.

 

[DavePayne]

Re: Dumb question of the day: Streetlighting Voltage

Thanks Peter.

That helps immensely.

Sheesh! You learn something new everyday. And here I thought I knew everything.

Dave.

 

[iwire]

Re: Dumb question of the day: Streetlighting Voltage

Dave you can find HID fixtures rated 120, 208, 240, 277 and 480 volts.

For street lighting it is usually best to pick the highest voltage available, sometimes it may even be more cost efficient to install a transformer to raise the voltage if all you have is 208 or 240 volts available.

The cost of the conductors needed to overcome voltage drop adds up quickly.

Here are the ratings of a typical 400 Watt HPS ballast.

Operating Current

@ 120 V 3.8 Amps

@ 208 V 2.2 Amps

@ 240 V 1.9 Amps

@ 277 V 1.7 Amps

@ 480 V 1.0 Amps

You can quickly see the advantage of running the highest voltage you can.

 

[DavePayne]

Re: Dumb question of the day: Streetlighting Voltage

Thanks Bob.

The City have already installed the transformers (120/240V) so I'm stuck with them.

One run is almost 1500 feet with 10, 400w fixtures on it. I thought I was going to have to use 120v and when I did the calculations the voltage drop was laughable.

At 240v the wire size and voltage drop will now be manageable, but I still think I'll have a hard time keeping it below 5%

 

[charlie]

Re: Dumb question of the day: Streetlighting Voltage

Interesting, we use 240/480 volt single phase for a lot of our street lighting circuits. We connect the lights from the phase to the neutral at 240 volts and use the neutral for grounding.

 

[George Stolz]

Re: Dumb question of the day: Streetlighting Voltage

I use 120V for our site lighting on my project. My technique is a few lights on one building, a few lights on the next, and so on. This way, I can use the small button photoeyes; if they fail they're inexpensive to replace, and lighting for the whole project doesn't go out at once.

I usually use 12 UF for the runs. They're never very long - I'd have to use that ucky roll of 10-3 UF that's been collecting dust in my garage.

 

[charlie]

Re: Dumb question of the day: Streetlighting Voltage

George, keep in mind that I am talking about street lighting that falls under the NESC. BTW unless the button type have changed, they are junk and I would only use the larger TL type.

 

[tom baker]

Re: Dumb question of the day: Streetlighting Voltage

I never use button photo eyes. They have a short life. Use the twist lock type, and get a shorting cap. You can install a shorting cap to test the lights during the day.
I prefer 240 over 120, its the same voltage to ground, but 25% less VD.
I would avoid 480 as its more hazardous, and the gear is more expensive.

 

[iwire]

Re: Dumb question of the day: Streetlighting Voltage

Originally posted by tom baker:
I would avoid 480 as its more hazardous, and the gear is more expensive.

I do not understand, the wiring is safe or not safe. If wired properly 120 to ground or 277 to ground makes no difference.

I guess we work on different size projects, even at 480 we often end up with 1 to 4 AWG Copper for voltage drop reasons.

 

[BruceH]

Re: Dumb question of the day: Streetlighting Voltage

Originally posted by peter d:


The 240/415 is a British voltage standard and not used in the U.S.

Just for information purposes, I worked in an older Hotel recently. 2 transformers were 416/240. I checked the actual voltages, 240 line to neutral, 416 line to line. Right here in Buffalo, N.Y.

[ October 10, 2005, 08:23 PM: Message edited by: BruceH ]

 

[kiloamp7]

Re: Dumb question of the day: Streetlighting Voltage

Bruce - Just curious, were these 1-phase xfmrs that were connected in a 3-phase bank ?
And with the voltage taps set to yield 416Y/240V. ?
That method can be used to yield a "poor man's 480Y/277V." by moving taps all the way & getting appx. 460/265.

 

[oliver100]

Re: Dumb question of the day: Streetlighting Voltage

Voltage drop and voltage dip for a roadway lighting:

It is little tricky to calculate, but it pays off if you calculate the voltage drop at evry lighting post. The further you go the less voltage drop is developed for each wiring segment.

One more suggestion. The inrush current of High Pressure Lamps is a factor when sizing the wires. Sometimes the lights cannot start if the voltage dip is excessive. And they dim if a high power motor is connected to the same power source without a soft start.

Worse come to worse the same wiring can be used by just increasing the voltage.