480 Volt Single Phase

[iwire]

Sorry Mel. It took me a few days to get my head around it also. 40 years experiance in the electricticial trade. EC and Fl State inspector and I find somthing new every day. 480 volt street lighting can and is 1 hot ,1 neutral, 1 ground. At least with Florida Power and Light.

Is it really a 'neutral' or is it just the grounded conductor?

 

[jmellc]

Not in this case.

In this case hot to grounded is 480.

1st I've heard of this. All 480 I ever did was 480 phase to phase & 277 phase to ground. So this is 480 phase to phase & 480 phase to ground? Granted, I didn't work with 480 every day, but enough that I knew some about it. What kind of transformer or generator was this fed from? And didn't OP say it was a 2 pole breaker? 2 pole breaker would mean 2 hot legs, unless only 1 breaker terminal was being used.

 

[jmellc]

Looking back through, I see I missed posts about 832 volt systems for motors, that would make sense for a 480 phase to ground. But OP said he was installing lights with 2 phase conductors & a gec, using a 2 pole breaker. That would be 480 single phase, double pole. Should be 480 phase to phase & 277 to ground. I'm pretty sure some of the wall packs & bollards I've installed had leads for 480. I remember for sure 277, 208 & 120 leads.

 

[iwire]

1st I've heard of this. All 480 I ever did was 480 phase to phase & 277 phase to ground. So this is 480 phase to phase & 480 phase to ground? Granted, I didn't work with 480 every day, but enough that I knew some about it. What kind of transformer or generator was this fed from? And didn't OP say it was a 2 pole breaker? 2 pole breaker would mean 2 hot legs, unless only 1 breaker terminal was being used.

I think, and I do not know for sure that Cavie is dealing with a simple single phase transformer with just a two wire output.

Not really any different than a doorbell transformer only the primary may be 7200 volts and the secondary 480 volts phase to phase to phase, once you ground one of the phases you would have 480 from the one remaining phase to ground.

 

[Transportation Guy]

480 VAC Street Lighting

480 VAC Street Lighting

We work on DOT street lighting in Charlotte, NC and it has a ton of 480 to ground serving it. My old boss called it a "bastard" service because it didnt need 2 ungrounded conductors to give you 480VAC. it was on 1 leg. Section 220.5 list 480 as a voltage in addition to 480Y/277.

Pete Landreth
Master electrician, IMSA Level II Traffic Signal Technician

 

[jumpingspidermedia]

480 VAC is produced as a 3 phase power source.Widely used for industrial applications.

This voltage is not typically considered single phase, it is Line - Line. The 480VAC is transformed into 120VAC/220VAC for typical control circuits after it enters a control cabinet.

 

[roger]

480 VAC is produced as a 3 phase power source.

480 V can also be derived from a stand alone single winding as disscussed in this thread.

Roger

 

[mivey]

480 VAC is produced as a 3 phase power source.Widely used for industrial applications.

This voltage is not typically considered single phase, it is Line - Line. The 480VAC is transformed into 120VAC/220VAC for typical control circuits after it enters a control cabinet.

Any one voltage by itself is a single-phase voltage. It does not matter if it is produced by an ungrounded-ungrounded conductor connection or by an ungrounded-grounded conductor connection. Only in combination with certain other voltages does a group of voltages become something other than individual single-phase voltages.

And you can get 480 volt single phase from a single phase connection as roger said and as have others apparently said (I have not read through the thread).

 

[jmellc]

That brings up a question with me. I think I know the answer but maybe not.

My license allows me to work up to 600 volts maximum. If the panel is 832, am I forbidden to enter the panel to run a 480 SP ckt or should I stay out of it because I'm opening an 832 volt source?

My thought is I can't work on it, as I'm exposing myself to more than 600 volts, regardless of only working with 1 leg.

 

[kwired]

That brings up a question with me. I think I know the answer but maybe not.

My license allows me to work up to 600 volts maximum. If the panel is 832, am I forbidden to enter the panel to run a 480 SP ckt or should I stay out of it because I'm opening an 832 volt source?

My thought is I can't work on it, as I'm exposing myself to more than 600 volts, regardless of only working with 1 leg.

I would say that is up to the agency that issued the license.

I have never heard of a voltage limit being attached to a license.

But then around here I only know of very few industrial places that have systems over 600 volts. Anything else over 600 volts is always POCO equipment.

I do know POCO guys that are well trained with over 600 volt as they should be, but they have no idea how to do safe wiring under 600 volts within a building.

 

[jmellc]

I would say that is up to the agency that issued the license.

I have never heard of a voltage limit being attached to a license.

But then around here I only know of very few industrial places that have systems over 600 volts. Anything else over 600 volts is always POCO equipment.

I do know POCO guys that are well trained with over 600 volt as they should be, but they have no idea how to do safe wiring under 600 volts within a building.

How true, I have done work at POCO guys' homes. I was shocked at some of the wiring they did.

I'm in North Carolina, limited license, good to 600 volts, project value $40,000.00.

Not that I'll ever the 480/832, most likely. I haven't heard of it anywhere here. 480 3/p is the highest I've worked with. I think 1 plant I used to work in had 600 in some areas.

 

[renosteinke]

There's nothing fancy, or unusual, about 480v lighting. Think of it as '240 on steroids.'

Look at it this way: the ballast needs a potential between the two ballast 'line' wires to work. If one is "+" at the same instant the other is "-," you have that potential. In a quirk of our language, we call this 'single phase,' though neither of the wires is at the same potential as ground.

A few little details I've learned about such installations:
First off, the 'multi-tap' ballasts generally do not work; you need a 480v ballast.

Second, troubleshooting is greatly eased if you have fuses in both 'hots' at the base of the pole.

Third, the 'circuit' might actually have three 'hots,' be fed by a three-phase breaker, yet only have two 'hots' going up each pole. That is, the first light might use phases AB, the second AC, the third BC, and on down the line. What fun! (Especially when a pole is knocked down and the scheme gets messed up.)

Such lights almost always have some form of automatic control. VERIFY that ALL power is off before you start taking things apart. Just because the bulb isn't lit - well, there's no guarantee that BOTH of the 'hots' are dead. Even if there's a photocell on the pole, there might be a contactor somewhere.

When designing such a system, you might want to provide an accessible disconnect, as well as a 'test' or 'manual' means, at the base of each pole.

 

[VIP]

NEC

NEC

What's the maximum alloable voltage for commercial pole lighting according to the NEC?

 

[VUGear]

Third, the 'circuit' might actually have three 'hots,' be fed by a three-phase breaker, yet only have two 'hots' going up each pole. That is, the first light might use phases AB, the second AC, the third BC, and on down the line. What fun! (Especially when a pole is knocked down and the scheme gets messed up.)

Are there any problems with doing this? Feeding 480V 1-phase fixtures on a 480V 3-phase circuit from a 480Y/277V source? I've been wondering about this.

 

[iwire]

Are there any problems with doing this? Feeding 480V 1-phase fixtures on a 480V 3-phase circuit from a 480Y/277V source? I've been wondering about this.

No problem at all and very common in large installations.