480V confusion

[Electron_Sam78]

I ran across astrange supply from the power company today. It's a 480V source coming from a bank of 3 pole top transformers. There are 3 legs that read around 500V phase to phase but if you go phase to ground 2 legs also read around 500V except one which reads 0 volts. We thought this was a problem with the supply but the power company said that's how they supply 480 for lighting loads in this area. The middle leg is grounded. I'm cornfused. I haven't worked with 480 V or dealt with transformer connections in years so I've forgotten a lot. Can someone explain this, speaking slowly and using pretty pictures? :-?

 

[Cavie]

Yep, this is 480v to ground 2 wire system. Used in street lighting. I learned about it 6 months ago.

 

[raider1]

It sounds like they have a 480 volt corner grounded delta system.

I don't have any pretty pictures at the moment but I am sure someone else has some.

Chris

 

[480sparky]

...........I don't have any pretty pictures at the moment but I am sure someone else has some.

Chris

Not pretty, but...........

 

[raider1]

Not pretty, but...........

I was thinking of you when I said someone would probably have a picture.

Thanks Ken.

Chris

 

[Cavie]

Not pretty, but...........

Nope, they bring you 2 wires, one hot 480v, one neutral. But ILL may due things different just like then politics

 

[raider1]

Nope, they bring you 2 wires, one hot 480v, one neutral. But ILL may due things different just like then politics

The orignal poster mentioned that there was 3 legs with a voltage between all three of 500 volts and only 2 had a voltage between them and ground with the third leg having a 0 voltage between it and ground. That leads me to believe this is a 3 phase corner grounded 480 volt system where the voltage is a little high.

Chris

 

[electricalperson]

heres something fun to read http://ecatalog.squared.com/techlib/docdetail.cfm?oid=09008926800b38e9

 

[Electron_Sam78]

Yes there are three wires. This is definitely a corner grounded delta (AKA grounded B) setup now that I've read the info on electricalperson's link.

 

[mickeyrench]

I know someone said its used for street lighting but there is a place i 've been to that has that type of service and they use it for 3 phase motors mostly. I there a draw back using this on motors?

 

[LarryFine]

I there a draw back using this on motors?

Nope. The loads don't care which, if any, conductor is grounded.