TM1238
Member
- Location
- Buffalo, NY
I am in the middle of an engineered project where the landlord provided a service configuration that did not match (or at least not make feasible) the one-line distribution drawings that the tenant required. We were asked by the tenant to suggest a resolution. I have re-designed the one-line, however, myself and a colleague in our company disagree on the requirements of protecting the load side conductors of a manual transfer switch. The scenario is as follows;
This part of the distribution and service is existing: The service is 225A, 480Y/277V, 3P4W. It is protected by an exterior N3R fusible safety switch and feeds an interior 225A enclosed circuit breaker.
This is the new portion of the distribution: The load side of the 225A ECB feeds the normal power section of a 400A manual transfer switch (located outside). The load side of the manual transfer switch feeds a 150 kVA transformer (located inside) which feeds a lineup of several MCB panelboards (also inside).
The emergency power section of the manual transfer switch is connected to a set of camlocks to allow the use of a roll-up generator. The manual transfer switch does not have any fusing.
This is where my colleague and I disagree; When the manual transfer switch is set to emergency power I believe that there is a possibility of inadequate OCP of the conductors between the load side of the manual transfer switch and the transformer. I see a violation here because the switch would allow up to a 400A feeder via the camlocks, greater than what the primary side of the transformer is able to accept per NEC. My colleague argues that no additional OCP is required between the load side of the transfer switch and line side of the transformer.
What say you? Thanks for your input.
This part of the distribution and service is existing: The service is 225A, 480Y/277V, 3P4W. It is protected by an exterior N3R fusible safety switch and feeds an interior 225A enclosed circuit breaker.
This is the new portion of the distribution: The load side of the 225A ECB feeds the normal power section of a 400A manual transfer switch (located outside). The load side of the manual transfer switch feeds a 150 kVA transformer (located inside) which feeds a lineup of several MCB panelboards (also inside).
The emergency power section of the manual transfer switch is connected to a set of camlocks to allow the use of a roll-up generator. The manual transfer switch does not have any fusing.
This is where my colleague and I disagree; When the manual transfer switch is set to emergency power I believe that there is a possibility of inadequate OCP of the conductors between the load side of the manual transfer switch and the transformer. I see a violation here because the switch would allow up to a 400A feeder via the camlocks, greater than what the primary side of the transformer is able to accept per NEC. My colleague argues that no additional OCP is required between the load side of the transfer switch and line side of the transformer.
What say you? Thanks for your input.
