480 volt 1 phase to 120/240 sec. bonding neutral

[roy g]

working 480 1 phase primary to 120/240 secondary transformer. transformer is fed from 480 volt 3 phase sub panel. Am I correct in that the neutral on the secondary side must be bonded to the transformer frame. thanks

 

[Smart $]

working 480 1 phase primary to 120/240 secondary transformer. transformer is fed from 480 volt 3 phase sub panel. Am I correct in that the neutral on the secondary side must be bonded to the transformer frame. thanks

Not necessarily direct, but it will be one way or the other. Assuming indoor xfmr, a GEC from the [grounded] neutral to the nearest of either a water pipe or structural-steel electrodes, or if not the nearest, the building GES. This bond can be either in the xfmr or first disconnecting means enclosure, the same enclosure as the system bonding jumper (SBJ).

If the SBJ is in the xfmr enclosure, it makes the connection to the frame.

If the SBJ is in the first disconnecting means enclosure, it and supply-side bonding jumper (SSBJ) will form the connection.

 

[augie47]

This may help


Note there are exceptions for transformers 1kw and less