Grounded or Grounding

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sogelectric

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I recently installed a service for a 480V 3 phase motor which is fed from a step-up transformer; Primary 208V-Secondary 480Y/277. The 208V 3 phase system comes from a transformer into a meter, from there into a 208V disconnect then into the step up transformer then into a 480V disconnect. From the 208V transformer I have 3 hot?s and a ground/grounded conductor going into the meter. Leaving the meter into my first 208V disconnect my grounded conductor is tied to the equipment and leaves to the transformer still 3 hot?s and a ground. Going into the transformer should this ground wire terminate at the frame connection or the XO or does it matter since it is all tied together? Once I leave the step-up transformer to go into the 480V disconnect do I need to bring in 3 hot?s a neutral and a ground in which I would isolate the neutral, or can I just keep 3 hot?s and a ground because I?m just using the 480V for a 3 phase motor and don?t need a neutral? If I use just 3 hot?s and a ground to my disconnect, the ground that goes out of the disconnect to my motor, would it be considered a grounded or grounding conductor?
FYI: My meter base grounding electrode conductor goes out of the meter connects to one ground rod then to another one, then into the step up transformer equipment ground.

Thanks
 
The conductor from the meter to your 208 disconnect would be a groundED conductor and sized per 250.24(C). The disconnect should be bonded.
From that disconnect to your step-up transformer you should have a groundING means that meets 250.118. (& 250.122 if its a conductor)
Nothing should connect to XO.
If you do not need a neutral for the 480v side there is no need for one (your transformer may or may not have terminals)
The transformer secondary grounding should be addressed per 250.30(B) and if necessary 250.21(B)
 
The ground wire on the primary side need to be terminated to the transformer case or to the grounding bar if the transformer have it. On the secondary side of your transformer you will have to install a system bonding jumper based on the table 250.66 in order to create a grounded system if not you will have an ungreded system and you will have to install a ground fault protection for it. You ground wire on the secondary side can originate on the XO terminal,transformer case or ground terminal inside of the transformer!!! System bonding jumper is the most important installation on the secondary side of a Y transformer.
 
There should be no connection of a grounded conductor to the 208V side of a transformer used in a step-up configuration.

Be aware of the actual terminal descriptions. You say your transformer is an actual step-up one, with a 208V primary and a 480Y/277V secondary if that is the case, then you will not have an X0 connection, however you will have an H0 one.
 
jim dungar said:
There should be no connection of a grounded conductor to the 208V side of a transformer used in a step-up configuration.

Be aware of the actual terminal descriptions. You say your transformer is an actual step-up one, with a 208V primary and a 480Y/277V secondary if that is the case, then you will not have an X0 connection, however you will have an H0 one.
Click to expand...

You are totally right it should be the HO terminal on the 277/480 side!!!
 
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