A colleague of mine has been referencing NEC 250.30. My colleague has stated that what I seem to understand is the exteranal pad mounted transformer and an external switch is not considered to be a separately derived system, but a MDP is seperately derived.
We have a configuration where utility power is connected to the external pad mounted transformer. The external pad mounted transformer is connected to an external switch. The external switch is connected to a existing switchboard on one end (a secondary run) and a new MDP (a secondary run) we are installing on the other end. The primary of the external switch is of course connected to the external pad mounted transformer.
My colleague has told me that the connection from the external pad mounted transformer to the external switch is not separately derived, so we can bond on the load side from the equipment ground and nuetral to the water pipes as well as ground to the grounding electrodes. But my colleague has said the MDP is separately derived so the nuetral can not be grounded on the load side per NEC 250.30(A), only my equipment ground is bonded to the water pipes and grounded to the grounding electrodes. The designer did the work this way. My nuetral is left floating on the load side of the new MDP we are installing.
We have a configuration where utility power is connected to the external pad mounted transformer. The external pad mounted transformer is connected to an external switch. The external switch is connected to a existing switchboard on one end (a secondary run) and a new MDP (a secondary run) we are installing on the other end. The primary of the external switch is of course connected to the external pad mounted transformer.
My colleague has told me that the connection from the external pad mounted transformer to the external switch is not separately derived, so we can bond on the load side from the equipment ground and nuetral to the water pipes as well as ground to the grounding electrodes. But my colleague has said the MDP is separately derived so the nuetral can not be grounded on the load side per NEC 250.30(A), only my equipment ground is bonded to the water pipes and grounded to the grounding electrodes. The designer did the work this way. My nuetral is left floating on the load side of the new MDP we are installing.