Grounding transformer secondary

[Barbqranch]

I am involved in planning the move of a large (for our facility) piece of equipment. It runs on 480 V 3P, and the plant is fed w/ 208Y/120. There is a Federal Pacific 45KVA transformer being used, which will remain.

However, in looking the existing over, I feel I must basically re-wire from transformer to machine. 120 feet.

Question: There is no ground connection on the delta output of the transformer. Do I need to corner ground it, and if so, am I risking any problems they haven't had before? It has run for years like it is. Measuring from ground to H1 I get around 50Kohm, but it is not a stable reading. Machine was turned off at it's main, as was the breaker locked out when I opened the transformer.

 

[augie47]

There is no requirement for you to corner ground the 480 output. If you elect to leave it ungrounded, 250.21(B) would require a ground detection system.
Before making a decision I would suggest talking the the equipment manufacturer.
Some equipment, especially where drives are installed, do not care for ungrounded ad/or corner grounded systems.

 

[Scali]

Had a similar situation,

Had a similar situation,

I am involved in planning the move of a large (for our facility) piece of equipment. It runs on 480 V 3P, and the plant is fed w/ 208Y/120. There is a Federal Pacific 45KVA transformer being used, which will remain.

However, in looking the existing over, I feel I must basically re-wire from transformer to machine. 120 feet.

Question: There is no ground connection on the delta output of the transformer. Do I need to corner ground it, and if so, am I risking any problems they haven't had before? It has run for years like it is. Measuring from ground to H1 I get around 50Kohm, but it is not a stable reading. Machine was turned off at it's main, as was the breaker locked out when I opened the transformer.

The A.H.J told me to run a ground wire from transformer case to the disconnect because, It was over ten feet and ground detectors are expensive.

 

[Scali]

Now this is if you are back feeding.