Why 277 volt lighting

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LarryFine

LarryFine

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Another consideration: You lose 2/3 of your lighting if you lose one line using L-L lights, but only 1/3 with L-N lights.
 
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GoldDigger

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mbrooke said:
Yup, that can happen at any voltage. At certain fault levels a bear suit simply provides the option of an open casket funeral.

But again I'm having trouble seeing how this applies to lighting branch circuits.
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Lighting branch circuits require panel boards, feeders, and mains.
 
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GoldDigger

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mbrooke said:
We we don't do is way better and history has shown that time and time again. Humans have to start living this way if we want our problems to go away. Highly practicable and productive. To say otherwise is purely fanatical dogma.
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FWIW:

“The reasonable man adapts himself to the world: the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.”
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---G. B/ Shaw
 
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paulengr

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mbrooke said:
Thanks for proving me right.

Anyways, can you give me a scenario regarding 480 volt arc flash and linemen?
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Not the same thing. Most pole line arcs are traveling arcs. They move away from the lineman before it even matters. Even when it stays around the heat is spread in open air which decreases in intensity much faster. Plus tons of equipment tests show most utility equipment has very low arc flash potential. That’s why NESC has vastly lower requirements for arc flash.

Arcs at 277 V are self sustaining. They self extinguish at 120 V. Big difference.
 
mbrooke

mbrooke

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hillbilly1 said:
Maybe, maybe not, just depends on how balanced or unbalanced the load is! LOL!
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Right- that is until the ballasts/drivers subjected to the over voltage condition short circuit. Then the otherwise under voltage equipment is hit with an over voltage.
 
mbrooke

mbrooke

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paulengr said:
Not the same thing. Most pole line arcs are traveling arcs. They move away from the lineman before it even matters. Even when it stays around the heat is spread in open air which decreases in intensity much faster. Plus tons of equipment tests show most utility equipment has very low arc flash potential. That’s why NESC has vastly lower requirements for arc flash.

Arcs at 277 V are self sustaining. They self extinguish at 120 V. Big difference.
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Right- but I'm talking about lighting branch circuits. #12 has a one way AC resistance of 2 ohms per 1000 feet.

How is a 480 volt florescent truffle more dangerous than one on 277 volts?
 
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SceneryDriver

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277V is only 15% higher than 240V. Seeing as virtually every other part of the world uses 240V for lighting, it's a no-brainer that manufacturers decided to build ballasts / power supplies with that supply range to accomodate a 15% tolerance, but not to accommodate 480V when the rest of the world doesn't use it. Ballasts / supplies can use the same semiconductors and same circuit boards, thus saving manufacturing costs.

Multinational manufacturers build products in such a way that they can be sold and used by the largest number of people. Building a special ballast / power supply just for the US market probably doesn't make sense when they can simply require us to run L-N and get a pretty-much-the-same voltage as the rest of the world.

SceneryDriver
 
mbrooke

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SceneryDriver said:
277V is only 15% higher than 240V. Seeing as virtually every other part of the world uses 240V for lighting, it's a no-brainer that manufacturers decided to build ballasts / power supplies with that supply range to accomodate a 15% tolerance, but not to accommodate 480V when the rest of the world doesn't use it. Ballasts / supplies can use the same semiconductors and same circuit boards, thus saving manufacturing costs.

Multinational manufacturers build products in such a way that they can be sold and used by the largest number of people. Building a special ballast / power supply just for the US market probably doesn't make sense when they can simply require us to run L-N and get a pretty-much-the-same voltage as the rest of the world.

SceneryDriver
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I'd agree for today, but think back in the past when US manufacturers were making magnetic 60 cycle ballasts with North America in mind.
 
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paulengr

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mbrooke said:
Right- but I'm talking about lighting branch circuits. #12 has a one way AC resistance of 2 ohms per 1000 feet.

How is a 480 volt florescent truffle more dangerous than one on 277 volts?
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480 phase to phase is still 277 to ground. There is a theoretical arc flash calculation which says that the arc energy is equal to V x I x time x conversion factor but it is fundamentally wrong. Voltage does affect arc flash but only a little bit. Fault current and time are the major factors.

This isn’t so much an arc flash issue but ungrounded 480 does some crazy things in an arcing fault.


The big difference is that typically lighting transformers are 10-100 kVA. It is naturally current limited so an arc is typically more of a spark. Getting it to self sustain is hard. If you had say a 50 kVA 480/277 isolation transformer it would be similar. But let’s face it you are running 277 or 480 because the engineer is being cheap. So the transformer is also running motor loads and it’s 300-1500 kVA. Fault current is crazy high and it’s no longer a little spark, it’s a fireball.

For lighting work the big hazard usually isn’t the arc flash itself. Ladder work isn’t safe because there is probably nothing to tie off to. OSHA fatality reports are filled full of reports of electricians dying not from the arc itself but getting startled and falling off ladders or out of man lifts. The arc flash itself doesn’t matter because the little tiny animal brain cerebellum at the base of your skull is going “bright lights, loud noise, flee!” and makes your body do things that get you killed when you flinch, jump back, or try to duck out of the way while perched on a ladder with both hands flailing. It’s a survival instinct. The cerebral cortex doesn’t get to react until a quarter second later. By then it’s too late.

While on the subject there is a third option: high resistance grounding. This keeps ground fault currents very low with minimal damage during a fault, makes it almost impossible to die from electrocution, makes arc flash very unlikely, and in larger systems it’s cheaper to install and maintain than solid grounding. The downside is that there is no neutral so 277 is not allowed and you just run 480. Second downside is troubleshooting can be a pain because you can’t just look for something burned up. Very popular in the mining industry, some chemical plants, and all over Europe where some countries require it. And under NEC it isn’t even allowed at 240/120.

With 480 it can arc a little easier. 600 V calls for 1” spacing between phases where 300 V calls for something like 1/2” in open air. And the arc is hotter because it has to jump a wider gap. But the difference in typical transformer kVA (short circuit current) more than makes up for this detail. Arguing voltage and arc flash is splitting hairs. The transformer impedance is what is driving it.

Another problem is 480 or 277 V in control circuits. It would be different running everything on a lighting contactor. But if you’ve ever seen what happens to controls back when motor circuits ran at straight 480 without a control power transformer, you’d think twice about it. When they fail the contacts tend to blow apart, launch parts, shoot flames out, and essentially scare people. Granted that little 2 A fuse blows pretty fast but 120 V controls just seems a lot safer.

Another practical issue is maintenance. A bad fixture can cause under/over voltage issues and destroy several more fixtures on that string of lights. And when you are working on a light string you don’t want to put the entire plant in the dark. There is a practical limit on how many fixtures you can put on a single string no matter what the voltage drop is. So the voltage drop argument doesn’t fly. By the time the improved VD helps with 480 there are practical reasons why it doesn’t matter.

I’ve done lots of jobs “downgrading” from 277 or 480 to 240 or 120. If you are arguing over 480 against 130 it’s a big difference. But for about the same cost you can use 240 and so the 480 advantage is now much smaller. Arguing 277 vs. 240 is silly unless we consider transformer impedance (short circuit, not %Z). So I’m firmly in the 240/120 camp as far as lighting is concerned.
 
mbrooke

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paulengr said:
480 phase to phase is still 277 to ground. There is a theoretical arc flash calculation which says that the arc energy is equal to V x I x time x conversion factor but it is fundamentally wrong. Voltage does affect arc flash but only a little bit. Fault current and time are the major factors.

This isn’t so much an arc flash issue but ungrounded 480 does some crazy things in an arcing fault.


The big difference is that typically lighting transformers are 10-100 kVA. It is naturally current limited so an arc is typically more of a spark. Getting it to self sustain is hard. If you had say a 50 kVA 480/277 isolation transformer it would be similar. But let’s face it you are running 277 or 480 because the engineer is being cheap. So the transformer is also running motor loads and it’s 300-1500 kVA. Fault current is crazy high and it’s no longer a little spark, it’s a fireball.

For lighting work the big hazard usually isn’t the arc flash itself. Ladder work isn’t safe because there is probably nothing to tie off to. OSHA fatality reports are filled full of reports of electricians dying not from the arc itself but getting startled and falling off ladders or out of man lifts. The arc flash itself doesn’t matter because the little tiny animal brain cerebellum at the base of your skull is going “bright lights, loud noise, flee!” and makes your body do things that get you killed when you flinch, jump back, or try to duck out of the way while perched on a ladder with both hands flailing. It’s a survival instinct. The cerebral cortex doesn’t get to react until a quarter second later. By then it’s too late.

While on the subject there is a third option: high resistance grounding. This keeps ground fault currents very low with minimal damage during a fault, makes it almost impossible to die from electrocution, makes arc flash very unlikely, and in larger systems it’s cheaper to install and maintain than solid grounding. The downside is that there is no neutral so 277 is not allowed and you just run 480. Second downside is troubleshooting can be a pain because you can’t just look for something burned up. Very popular in the mining industry, some chemical plants, and all over Europe where some countries require it. And under NEC it isn’t even allowed at 240/120.

With 480 it can arc a little easier. 600 V calls for 1” spacing between phases where 300 V calls for something like 1/2” in open air. And the arc is hotter because it has to jump a wider gap. But the difference in typical transformer kVA (short circuit current) more than makes up for this detail. Arguing voltage and arc flash is splitting hairs. The transformer impedance is what is driving it.

Another problem is 480 or 277 V in control circuits. It would be different running everything on a lighting contactor. But if you’ve ever seen what happens to controls back when motor circuits ran at straight 480 without a control power transformer, you’d think twice about it. When they fail the contacts tend to blow apart, launch parts, shoot flames out, and essentially scare people. Granted that little 2 A fuse blows pretty fast but 120 V controls just seems a lot safer.

Another practical issue is maintenance. A bad fixture can cause under/over voltage issues and destroy several more fixtures on that string of lights. And when you are working on a light string you don’t want to put the entire plant in the dark. There is a practical limit on how many fixtures you can put on a single string no matter what the voltage drop is. So the voltage drop argument doesn’t fly. By the time the improved VD helps with 480 there are practical reasons why it doesn’t matter.

I’ve done lots of jobs “downgrading” from 277 or 480 to 240 or 120. If you are arguing over 480 against 130 it’s a big difference. But for about the same cost you can use 240 and so the 480 advantage is now much smaller. Arguing 277 vs. 240 is silly unless we consider transformer impedance (short circuit, not %Z). So I’m firmly in the 240/120 camp as far as lighting is concerned.
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Right- but I'm talking about about having 480 volt trouffers in an office building. Not the service, not working live,not ungrounded systems ect. I can't see 480 making any negative difference.
 
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GoldDigger

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I know you say "not working live" but if there is a risk of live work, even just relamping, the difference between 480 and 277 can be the difference between a painful and a fatal shock.
 
mbrooke

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GoldDigger said:
I know you say "not working live" but if there is a risk of live work, even just relamping, the difference between 480 and 277 can be the difference between a painful and a fatal shock.
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I guess I could understand in terms of the screw shell now being live on an HID fixture... but if you get hit it will either be the open circuit voltage which in high wattage fixtures is often well above 277; or 277 volts before the ballast even if its hooked phase to phase. To me this argument is like saying a stove or clothes dryer is more dangerous because its on a 240 volt circuit.
 
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