- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I'm reviewing a design for a marine application (i.e., passenger ferry). The NEC does not apply, but I'd like opinions anyway.
The source of shore power is being changed from 240V to 480V, so the ferry must be modified to accommodate this change. The ferry's main panel is 240V 3 phase. A new 480V MLO panelboard will have 2 breakers. The shore power receptacle and conductors on the forward end of the vessel will be run to one breaker, and those from the aft end will be run to the other breaker. So the two breakers will serve as the disconnecting means to the panel. A mechanical interlock will prevent both breakers from being closed at the same time.
There are a total of 18 slots on the panel. Of these, 6 will be taken up by the two shore power breakers. But the vessel has no 480V loads, so the 12 unused slots have no purpose.
It appears to me that they intend to connect the panel's MLO termination points to conductors that will serve the primary of a 480/240V transformer. The transformer secondary will run to a breaker on the main switchboard. Each of the two breakers on the new panel is rated at less than 100% of the transformer's primary current rating.
Question 1: Is it OK to have power come in via a breaker and out via the MLO terminals?
Question 2: Can the pair of shore power breakers serve as overcurrent protection for the transformer primary?
ASIDE to Bob (Iwire): Let's not mention any company names, but I believe this project is taking place in your neck of the woods.
The source of shore power is being changed from 240V to 480V, so the ferry must be modified to accommodate this change. The ferry's main panel is 240V 3 phase. A new 480V MLO panelboard will have 2 breakers. The shore power receptacle and conductors on the forward end of the vessel will be run to one breaker, and those from the aft end will be run to the other breaker. So the two breakers will serve as the disconnecting means to the panel. A mechanical interlock will prevent both breakers from being closed at the same time.
There are a total of 18 slots on the panel. Of these, 6 will be taken up by the two shore power breakers. But the vessel has no 480V loads, so the 12 unused slots have no purpose.
It appears to me that they intend to connect the panel's MLO termination points to conductors that will serve the primary of a 480/240V transformer. The transformer secondary will run to a breaker on the main switchboard. Each of the two breakers on the new panel is rated at less than 100% of the transformer's primary current rating.
Question 1: Is it OK to have power come in via a breaker and out via the MLO terminals?
Question 2: Can the pair of shore power breakers serve as overcurrent protection for the transformer primary?
ASIDE to Bob (Iwire): Let's not mention any company names, but I believe this project is taking place in your neck of the woods.