480 Volt Single Phase

[InspecThis]

I have been under the impression that 480 is only three phase. I have a Parking Lot light with 480 volts........only two phase wires and one ground. Is this right or should I have 3 phase wires and a ground........no neutrals are run to the pole. The breaker feeding these lights are 2 pole 20 amp.

 

[iwire]

There are plenty of things that utilize 480 volt single phase, site lighting is one common example.

 

[Cavie]

I have been under the impression that 480 is only three phase. I have a Parking Lot light with 480 volts........only two phase wires and one ground. Is this right or should I have 3 phase wires and a ground........no neutrals are run to the pole. The breaker feeding these lights are 2 pole 20 amp.

480 volt street lighting. One phase wire, 1 neutral, 1 ground.

 

[roger]

There are a number items that utilize single phase 480, along with the mentioned site lighting, there are pumps, fan motors, some commercial cooking equipment, transformers, to name a few.

Roger

 

[iwire]

480 volt street lighting. One phase wire, 1 neutral, 1 ground.

Lets not confuse him, the 480 volt system he is using does not have a neutral at the poles and most will not.

The system you work on is unusual for NEC applications.

 

[Cavie]

Lets not confuse him, the 480 volt system he is using does not have a neutral at the poles and most will not.

The system you work on is unusual for NEC applications.

Just trying to show a 3rd system he didn't know about. I learned of at after only 40 years.

 

[iwire]

Just trying to show a 3rd system he didn't know about. I learned of at after only 40 years.

So you got in the trade at 5 years old.

 

[LarryFine]

I have been under the impression that 480 is only three phase.

Just about any voltage could be supplied from, and/or provided as single or three phase. It's true that 480v is a common commercial/industrial 3ph service voltage, and as either Delta or Wye.

I have a Parking Lot light with 480 volts........only two phase wires and one ground. Is this right or should I have 3 phase wires and a ground........no neutrals are run to the pole. The breaker feeding these lights are 2 pole 20 amp.

It's really no different than obtaining 208v 1ph from a 208Y/120v 3ph supply, or even from a (rare, but possible) 208v Delta 3ph secondary. The neutral makes bonding convenient even if the load doesn't need it.

Your supply could be either Delta or Wye, and it may be single or three phase. It doesn't really matter; just treat every conductor as ungrounded. (The panel the 2-pole breaker is in has all the answers. )

 

[LarryFine]

So you got in the trade at 5 years old.

I'm kinda close; I wired our shed when I was around 10 or 11.

 

[iwire]

I'm kinda close; I wired our shed when I was around 10 or 11.

DIY work does not count .... if it did I got you beat.

 

[haskindm]

480 volt street lighting. One phase wire, 1 neutral, 1 ground.

A single 480-volt phase wire and a neutral would give you 277-volts unless it is a corner grounded system, just as on a 120/240 volt system one phase conductor and the neutral give you 120 volts. With a 480 volt single phase you would need two hot conductors (ungrounded conductors) and a grounding conductor - no neutral required.

 

[Cavie]

So you got in the trade at 5 years old.

Nope, got in at 18. learned of 480 2 wire after 40 in the business. I'm 59 and 7/8.

 

[Cavie]

A single 480-volt phase wire and a neutral would give you 277-volts unless it is a corner grounded system, just as on a 120/240 volt system one phase conductor and the neutral give you 120 volts. With a 480 volt single phase you would need two hot conductors (ungrounded conductors) and a grounding conductor - no neutral required.

I'm not going to say your are wrong. I am going to say you just have not run accross this system as I had not when I got into street lighting. I thought the guys working for me were nuts!!! It is infact 480 volts 2 wire. 1 hot 1 neutral. It took me a few days to get my head wraped around it. It is used through out Florida distributed by FPL. Been doing this for over 40 years and I learn somthing new every day.

 

[dkidd]

OP said the breakers were 2-pole.

 

[dbuckley]

It is infact 480 volts 2 wire. 1 hot 1 neutral.

Strictly, one hot, and one combined neutral / ground conductor.

 

[Cavie]

Strictly, one hot, and one combined neutral / ground conductor.

Nope, 1 hot, 1 neutral, 1 ground. Blk, Wht, Grn. It's run in pvc or hdpt conduit.

 

[kwired]

I'm not going to say your are wrong. I am going to say you just have not run accross this system as I had not when I got into street lighting. I thought the guys working for me were nuts!!! It is infact 480 volts 2 wire. 1 hot 1 neutral. It took me a few days to get my head wraped around it. It is used through out Florida distributed by FPL. Been doing this for over 40 years and I learn somthing new every day.

I can see it as possible but I would think that it would make more sense to use a 480/240 center tapped transformer. Would not cost any more or less to install, other than whatever cost difference there is in transformer. It is likely same transformer just not with the center tap connected to anything. You get to save cost of one conductor between transformer and service equipment, everything else is same. I would rather see 240 volts to ground instead of 480, just for a little more safety should someone be exposed to live conductors.

 

[roger]

I can see it as possible but I would think that it would make more sense to use a 480/240 center tapped transformer. Would not cost any more or less to install, other than whatever cost difference there is in transformer. It is likely same transformer just not with the center tap connected to anything. You get to save cost of one conductor between transformer and service equipment, everything else is same. I would rather see 240 volts to ground instead of 480, just for a little more safety should someone be exposed to live conductors.

You would need to present your opinion to FPL and see if it went anywhere. I would say these are probably the cheapest installations can provide at this voltage.

Roger

 

[kwired]

You would need to present your opinion to FPL and see if it went anywhere. I would say these are probably the cheapest installations can provide at this voltage.

Roger

Street and area lighting is generally installed and serviced by qualified people so it is a little different but around here there is a lot of 480 volt services (single phase and 3 phase) for irrigation equipment and a lot of maintenance and some installation by not so qualified people.

I have never seen a single phase service that was not 240/480 center tapped transformer. Years ago there was a lot of corner grounded 480 volt delta systems around, but the POCO's around here have made all of them 277/480 or 240/480 (usually open delta in that case) because they did not like the idea of 480 volts to ground plus not many really understood that grounded phase all that well.

I knew of a farmer once that kept blowing a fuse at the service disconnect, so he decided to move the slug that was installed on the grounded phase to the position of the fuse that kept blowing. He said it was not long and there was a fire on one of the transformers so he turned it off and switched the slug back before calling the power company. - Another good reason to not have such a system where non qualified people are going to attempt to service it on a regular basis.

 

[roger]

Street and area lighting is generally installed and serviced by qualified people so it is a little different

You are correct. In South FL when speaking of traffic and road lighting the services Cavie is speaking of are strictly for these installations. The contractors or DOT employees working on these traffic signals know what they're dealing with when they open a cabinet or controller.

Roger