480V Single Phase with Grounded Leg

[jbt260]

I am looking for a way create a 480V single phase feeder with one leg grounded. The load is 48KVA. I am trying to create this from a 480/277V, three phase feeder. Does anyone make a 50KVA, 480V-480V single phase transformer ?

Thanks in advance!

 

[bob]

I am looking for a way create a 480V single phase feeder with one leg grounded. The load is 48KVA. I am trying to create this from a 480/277V, three phase feeder. Does anyone make a 50KVA, 480V-480V single phase transformer ?

Thanks in advance!

Why do you have to have one leg grounded? Take 2 of the 3 phases plus an egc and you have 480 volts single phase.

 

[jbt260]

Sorry for lack of info. I have to re-feed an existing roadway lighting circuit that is 480V single phase with a grounded leg. The leg is grounded at every light pole.

 

[bob]

Sorry for lack of info. I have to re-feed an existing roadway lighting circuit that is 480V single phase with a grounded leg. The leg is grounded at every light pole.

I am not sure that meets the NEC groounding requirements. I believe you need a EGC to each pole rather that using the neutral. Maybe someone will confirm this.

 

[Cavie]

480 2 wire single phase. 1 hot 1 neutral and a ground. Very common in street lighting. Something I learned after being an electrican for 40 years.

 

[Cavie]

Sorry for lack of info. I have to re-feed an existing roadway lighting circuit that is 480V single phase with a grounded leg. The leg is grounded at every light pole.

Check with your local POCO. Why arn't they supplying you?

 

[brian john]

480 2 wire single phase. 1 hot 1 neutral and a ground. Very common in street lighting. Something I learned after being an electrican for 40 years.

480 VAC Single phase is one hot, one grounded conductor and one EGC. I would think?

 

[Johnmcca]

Brian,
One hot, one grounded, and one EGC on a 480 systm would yeild 277 volt, unless I'm mistaken.

 

[Cavie]

Brian,
One hot, one grounded, and one EGC on a 480 systm would yeild 277 volt, unless I'm mistaken.

It is 480 1 leg to ground.

 

[jim dungar]

Brian,
One hot, one grounded, and one EGC on a 480 systm would yeild 277 volt, unless I'm mistaken.

Only if you are starting from a 480Y/277V system.

A single phase 480:480 transformer, like the OP asked about, could be used to create a 480 2-wire secondary which could then be treated the same as any other 2-wire system.

 

[LarryFine]

Brian,
One hot, one grounded, and one EGC on a 480 systm would yeild 277 volt, unless I'm mistaken.

You could be mistaken. The voltage between circuit conductors is all the load cares about.

Each conductor's voltage to ground depends solely on which supply conductor is grounded.

 

[benaround]

. The leg is grounded at every light pole.

jbt, What does this mean?

 

[mattsilkwood]

Someone please tell me if im wrong, but wouldn't a regular 480v circuit (480 L1-L2) do the same thing? the light isnt going to know if one conductor is grounded, and you're not going to bond the poles.

 

[jbt260]

A tfmr manufacturer came up with a solution for a 50KVA, 480V-480V, single phase transformation. They suggest using two 25KVA, 240x480V Primary, 120/240V Secondary, single phase transformers. You wire the primaries in parallel for 480V. You wire the secondaries in series for 480V. See attached diagram. Any thoughts are welcome !

 

[Pierre C Belarge]

This sounds like a Utility supplied street lighting job.

The grounded conductor is the utility's method of bonding all metallic parts. (similar to how we bond the neutral on the line side of the service disconnect)


jbt
Are you extending the street lighting?
Can you splice onto the existing street lighting wiring as it exists?

 

[jbt260]

Roadway lighting circuit at a highway rest area. Circuit is fed from the rest area building. Had to re-feed circuit due to renovation of rest area building. Lighting control contactors located in rest area building. This is my demarc point.

 

[Cavie]

Roadway lighting circuit at a highway rest area. Circuit is fed from the rest area building. Had to re-feed circuit due to renovation of rest area building. Lighting control contactors located in rest area building. This is my demarc point.

I have to ask again. Why not have POCO supply you with 480 single phase. It's already there. If that was the origional to the building, they should be able to hit your temp/new service as well.

 

[gmtt]

I don't get it. Why do you need a transformer when you have available source at 480V and your load need a 480V? If the source can accommodate the load, just take two phases from existing 480V 3-phase system and connect across the lights. Lights are heater element, and as long as the voltage across the filaments is 480V, it will be happy to glow at its rated power. As for ground, run ground conductor from the source and bond it to the metal pole. If ground is not available (for delta secondary), run a local ground properly and bond it the pole. That should suffice.

 

[Cavie]

I don't get it. Why do you need a transformer when you have available source at 480V and your load need a 480V? If the source can accommodate the load, just take two phases from existing 480V 3-phase system and connect across the lights. Lights are heater element, and as long as the voltage across the filaments is 480V, it will be happy to glow at its rated power. As for ground, run ground conductor from the source and bond it to the metal pole. If ground is not available (for delta secondary), run a local ground properly and bond it the pole. That should suffice.

If his system is a true 480 2 wire street lighting system he can not use 2 legs of a 480 3 wire system. It is 480v one leg to grouond. 1 black hot, 1 white neutral, and a green ground wire. Yes, the lights will work and wont know the differance but you can get someone killed down stream doing that. The control panels use the neutral in the coils and photo cells.

To add to this confusion is a 240/480 2 wire system. 2 240v hot legs and a ground.

I have 5 projects going right now and have trouble remebering which system is in use and screw up the wire colors and number of fuses needed on which job.

 

[gmtt]

If it involves control circuitry, needing a natural wire, then one solution I see, as someone else has eluded above, is to use an isolation transformer 480/480V, same KVA rating, with one leg of the secondary being grounded, and run a natural from the grounded leg..