Grounded or Ungrounded 240 Delta for Power

[bcoontz]

Good Morning!
We "currently" have an Ungrounded 240V Delta for supplying equipment that can't use 480V
We have the option, in our new plant of having the 3 phase 240V Power Panels wired either Ungrounded Delta or Corner Grounded Delta.
Any Pro's or Con's on either system?

Thanks!
Bob

 

[petersonra]

Re: Grounded or Ungrounded 240 Delta for Power

I guess it depends on whether you want a grounded power system or not. Personally, if I was going grounded I would want a wye ocnfiguration, but that is just a personal preference because I rarely if ever see corner grounded anything.

The primary reason for an ungrounded system is if your plant cannot tolerate a ground fault very well. If you can live with a ground fault tripping your power, than go grounded. If not, then go ungrounded. Its as simple as that.

 

[kiloamp7]

Re: Grounded or Ungrounded 240 Delta for Power

If it is in fact, a totally new plant, then wouldn't the first choice be 480/277 wye with xfmrs to derive 208/120 wye.
Then use xfmrs to derive any "special" voltages that are needed such as 240.
Generally for 3-phase 240V., I would prefer a system with a grounded conductor (whether the grounded conductor actually serves load or not).

 

[jim dungar]

Re: Grounded or Ungrounded 240 Delta for Power

Ungrounded distribution systems require a highly degree of troubleshooting experience. Many electricans are not trained on finding ground faults in ungrounded systems.

Corner grounded systems require non-standard distribution equipment (i.e. Square D QO2xxH breakers not QO2xx style).

At least one industrial in this area is now buying transformers with 240Y/138 secondaries. This is a standard rating for drive isolation designs. This arrangement gives them the advantages of 240V not 208V line to line and a center grounded distribution. They only feed 3 phase loads from these panels.

edit: fixed part number of breakers

[ September 28, 2005, 12:36 PM: Message edited by: jim dungar ]