francis.key19
Member
- Location
- frederick, md
Hi,
At our site, we have two 2500KVA service transformers (12470v primary, 480v secondary). X0 terminal is not grounded and not brought inside the building.
On one of the transformer, the X0 terminal is connected to the frame of the transformer. This transformer is a wye-wye transformer.
On the other of the transformer, the X0 is not connected at all. This transformer is a delta-wye.
For many years, the folks here thought that these are delta ungrounded systems on secondary side. There is no ground fault detector in either of the transformers. My questions are:
1. Is this a violation of the NEC code.?
2. Should we have the X0 grounded and bonded to a ground electrode? What would be the impact to existing three phase systems.?
3. Do we need to install ground fault detector? There are no main CB on either transformer (secondary side), but there are several conductors leaving the secondary and wired to indivisual CBs (i.e. no bus or switchboard) mounted on walls. Is this allowed under NEC?
4. For many years, one phase could go to ground and noone would know it until the next phase go to ground. This created havoc with the equipment. I am looking for suggestions on how to improve safety of these systems. The site is over 60 years old and we just recently came upon this.
5. What would be the impact of not grounded the X0 as related to short circuit and arc flash.
Thank you in advance for your help and guidance.
Regards,
FK19
At our site, we have two 2500KVA service transformers (12470v primary, 480v secondary). X0 terminal is not grounded and not brought inside the building.
On one of the transformer, the X0 terminal is connected to the frame of the transformer. This transformer is a wye-wye transformer.
On the other of the transformer, the X0 is not connected at all. This transformer is a delta-wye.
For many years, the folks here thought that these are delta ungrounded systems on secondary side. There is no ground fault detector in either of the transformers. My questions are:
1. Is this a violation of the NEC code.?
2. Should we have the X0 grounded and bonded to a ground electrode? What would be the impact to existing three phase systems.?
3. Do we need to install ground fault detector? There are no main CB on either transformer (secondary side), but there are several conductors leaving the secondary and wired to indivisual CBs (i.e. no bus or switchboard) mounted on walls. Is this allowed under NEC?
4. For many years, one phase could go to ground and noone would know it until the next phase go to ground. This created havoc with the equipment. I am looking for suggestions on how to improve safety of these systems. The site is over 60 years old and we just recently came upon this.
5. What would be the impact of not grounded the X0 as related to short circuit and arc flash.
Thank you in advance for your help and guidance.
Regards,
FK19