Transformer bonding jumper or not?

[lester.cape]

Need some help? We are going to install a 112.5 KVA Delta WYE transformer to step up the voltage from 120/208 to 277/480 to power a large piece of equipment. My question is this ( is a indoor type drypack transformer fed from a service disconnect who's power is derived from another transformer still considered and seperately derived system?). I am thinking yes because there is no direct electrical connection between the two voltages other than ground. I think it does need to have a main bonding jumper installed. My co-workers think not because there is already a main bonding jumper in the transformer the feeds the sevice dissconnect that is going to feed this new transformer. I am aware that you can only make this connection at the transformer, meter encloser, or the service disconnect. What do you guys think? Is this second transformer seperately derived from the first. Do I need a bonding jumper or not? If not can someone help me understand how a fault on this peice of equipment could get back to the source if I don't make this connection.

 

[infinity]

So the secondary is WYE? So this isn't a standard reverse connected Delta/WYE setup?

 

[raider1]

Yes, your second transformer would be a separately derived system and need a system bonding jumper.

Chris

 

[jim dungar]

Need some help? We are going to install a 112.5 KVA Delta WYE transformer to step up the voltage from 120/208 to 277/480 to power a large piece of equipment.

This is kind of confusing. I don't care what your existing L-N voltage is, it makes no difference to the final answer.

Is your transformer a 208V delta primary to a 480Y/277 wye secondary? If yes, then treat it like any other transformer you have ever connected including the grounding and bonding of the secondary neutral.

If your transfromer is a reverse connected transfromer you will be wiring it as a 208V primary (no neutral) to a 480V delta secondary. At this point you will need to decide if you are going to creae a grounded or ungraounded secondary.

 

[Strathead]

I am thinking yes because there is no direct electrical connection between the two voltages other than ground. I think it does need to have a main bonding jumper installed. My co-workers think not because there is already a main bonding jumper in the transformer the feeds the sevice dissconnect that is going to feed this new transformer.

It is apparent to me that you know the answer to this question. Definition of a separatley derived system is section 100 of the NEC. and you used the same wording so you know. Tell your code workers that as soon as they show you a "direct electrical connection" you will remove the bond jumper. Simple as that.