Delta 480 to delta 240 transformer 3 phase no neutral "B" phase to ground ?

Sparky129

Member
Location
ohio
Occupation
electrician
I have a delta 3 phase 480v transformer to 240v delta secondary no neutral .The question is do I ground "B" phase to ground and mark it with orange tape and label everything caution "B" phase grounded.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Orange would be used for 'high leg' delta. This happens when your delta has a grounded mid-point tap.

If you ground B phase, it is a _grounded_ conductor, and should be colored _white_. Labeling uncommon systems is always a good idea even if not required.

-Jon
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I have a delta 3 phase 480v transformer to 240v delta secondary no neutral .The question is do I ground "B" phase to ground and mark it with orange tape and label everything caution "B" phase grounded.
To ground one leg is a design choice. You can ground it and create a corner grounded system, or you can operate it as an ungrounded system and install a ground detector for the system.

If you make it a corner grounded system, the grounded conductor must be white or gray, as Jon said in the previous post.

Other than the voltage, a corner grounded systems installs just like a single phase 120/240 system. In many cases you can even use single phase equipment for the corner grounded system, but it is typically installed using 3 phase equipment and 3 phase breakers.

Note that "slash" rated breakers are not permitted...the breakers must have as single voltage rating that equals or exceeds the system voltage.

If you are using 3 phase fusible disconnects, you will need a "dummy" fuse for the grounded phases as any overcurrent protective device that opens the grounded conductor must simultaneously open the ungrounded conductors and fuses can't do that. (there is an exception for where the fuses are used to provide motor overload protection)
 

Sparky129

Member
Location
ohio
Occupation
electrician
To ground one leg is a design choice. You can ground it and create a corner grounded system, or you can operate it as an ungrounded system and install a ground detector for the system.

If you make it a corner grounded system, the grounded conductor must be white or gray, as Jon said in the previous post.

Other than the voltage, a corner grounded systems installs just like a single phase 120/240 system. In many cases you can even use single phase equipment for the corner grounded system, but it is typically installed using 3 phase equipment and 3 phase breakers.

Note that "slash" rated breakers are not permitted...the breakers must have as single voltage rating that equals or exceeds the system voltage.

If you are using 3 phase fusible disconnects, you will need a "dummy" fuse for the grounded phases as any overcurrent protective device that opens the grounded conductor must simultaneously open the ungrounded conductors and fuses can't do that. (there is an exception for where the fuses are used to provide motor overload protection)
thanks,the transformer now is no phase to ground and the first thought was to keep "B" phase that way but it seems there are 2 choices ;take "B" to ground or install ground indicator lights on the equimpment.It would seem easier just to ground "B".Far as identifying the "B" phase in field do I use white instead of orange
 

Sparky129

Member
Location
ohio
Occupation
electrician
Orange would be used for 'high leg' delta. This happens when your delta has a grounded mid-point tap.

If you ground B phase, it is a _grounded_ conductor, and should be colored _white_. Labeling uncommon systems is always a good idea even if not required.

-Jon
thanks
 
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