Transformer grounding

[Grouch1980]

Hey all,
Basic question here... I came across some transformers in an old building... they are all 480 volt - 208/120 volt, step-down transformers... some are 500KVA, 225KVA, 150KVA, etc. The enclosure of each transformer is labeled 'Secondary Grounded'. There was however no grounding electrode conductor that goes to building steel or cold water pipe for any of the transformers. The primary and secondary ground conductors were connected to the transformer ground bus, and a jumper went from the XO terminal to the ground bus and the neutral wire was connected to the XO terminal. Is the secondary of this transformer truly grounded? or does the code require that grounding electrode conductor?

Thanks.

 

[electrofelon]

Hey all,
Basic question here... I came across some transformers in an old building... they are all 480 volt - 208/120 volt, step-down transformers... some are 500KVA, 225KVA, 150KVA, etc. The enclosure of each transformer is labeled 'Secondary Grounded'. There was however no grounding electrode conductor that goes to building steel or cold water pipe for any of the transformers. The primary and secondary ground conductors were connected to the transformer ground bus, and a jumper went from the XO terminal to the ground bus and the neutral wire was connected to the XO terminal. Is the secondary of this transformer truly grounded? or does the code require that grounding electrode conductor?

Thanks.

A separately derived system always requires a grounding electrode connection to the metal parts, but the system does does not necessarily need to be grounded. That manufacturers statement was likely referring to the factory installed bonding jumper between XO and the ground buss. "Secondary bonded" or "system bonding jumper installed" would have been a better choice of words.

 

[Grouch1980]

A separately derived system always requires a grounding electrode connection to the metal parts, but the system does does not necessarily need to be grounded. That manufacturers statement was likely referring to the factory installed bonding jumper between XO and the ground buss. "Secondary bonded" or "system bonding jumper installed" would have been a better choice of words.

I see what you're saying... and it makes sense... "Secondary grounded" looks like it means the bonding within / inside the transformer. The manufacturer has no say as to what is installed outside (the grounding electrode conductor). If the nameplate says 'secondary grounded', it's whatever the manufacturer installed, which in this case is the bonding jumper only.