430-36?

[s wayne cook]

Hey Bennie, I posted a question about what a 3 wire, 3 phase ac system with one conductor grounded was. I'm still not sure that I get it. With only 3 wires, and one is grounded, how can this be 3 phase? Don't get too far beyond what my poor pea brain can understand please.
Ref. 430-36, 1999 NEC.
Wayne Cook

 

[iwire]

Re: 430-36?

Check this link out

Corner Grounded 3? 3 Wire

In the 1999 NEC check out 250-26(4)

[ April 14, 2003, 08:49 PM: Message edited by: iwire ]

 

[s wayne cook]

Re: 430-36?

Thanks Bob,
I can easily see how the system is designed.
Is this type of system prevalent in some parts of the country, or perhaps in some types of industry?
Is there some addvantage to a system like this?
Wayne

 

[frenchelectrican]

Re: 430-36?

yeah but we have few commercal and industal usage have corner ground phase but just bear in mind that most POCO are phasing them out due confuseing and safety confect i work on corner ground system quite a bit but it is no fun if you are not carefull with it. most of them allready switching to wye connetion now but few and i mean very few have specal permisson to use corner ground delta system reguarding what voltage now is rare now in my area if need more question i can try to set up a listing from my POCO'S regulation and voltage and size (ampcapity)


merci marc

 

[s wayne cook]

Re: 430-36?

Thanks Marc,
Wayne

 

[charlie]

Re: 430-36?

most POCO are phasing them out due confuseing and safety confect

Marc, the corner grounded delta is fairly common, esp. for small lift stations in this area. An open delta can be used with a triplex service drop to a single phase type service panel using full voltage 240 volt two pole circuit breakers. Two phases and the grounded conductor make a full three phase circuit to run three phase motors.

Wayne, any isolated secondary may be grounded one time anywhere and it just picks up a reference to ground, the configuration remains the same. It is sort of like touching a hot wire; the circuit doesn't have a complete path until the second phase is contacted. With that in mind, you can ground either end or the center of a 120/240 volt secondary of a single phase transformer and it will work fine until the second ground is established. The same applies to a three phase bank. You can even ground a phase wire and it will work.

Please don't loose sight of the fact that most of this doesn't meet Code but it does work.

 

[templdl]

Re: 430-36?

The way I consider a corner grounded delta is that the grounded conductor is treated similar to a neutral conductor as far as overcurrent protection is concerned. If fuses are used the grounded phase is not fused. However, a 3-pole breaker can be used because all 3 phases are opened simultaneously.
Also, after leaving the grounded point at the transformer the grounded phase conductor is never grounded again the same as a grounded neutral conductor.
However, the difference between a neutral and the grounded phase of a delta is that the neutral carried unbalanced current where the grounded phase is a load carrying conductor that happens to be grounded at its source.
The EGC is applied as any grounding conductor would be in a 1ph3w, 3ph,4w, etc. grounded systems.