We are a switchgear manufacturer and we are currently designing a selective type (main-tie-main) switchgear for a secondary unit substation. Now, our problem is whch type of tie CB are we going to use? 3P or 4P? The nominal LV side is 480Y/277V, 3-phase, 5W (T-N-S). Type of application is for semiconductor's firm wherein non-linear types of loads are very common.
The firm is following the ANSI standard, in which single point grounding is very common, However, contrary to that they specify on their specifications that the single point grounding is not acceptable which we agreed and seconded. However, one of their engrs says that, 3P is okay because they have no L-N loads and the 4th conductor has no longer use. Can we use 3P tie CB though we have a 4th conductor? Because of that comment, nothing is fixed right now, can you help us somehow?
The firm is following the ANSI standard, in which single point grounding is very common, However, contrary to that they specify on their specifications that the single point grounding is not acceptable which we agreed and seconded. However, one of their engrs says that, 3P is okay because they have no L-N loads and the 4th conductor has no longer use. Can we use 3P tie CB though we have a 4th conductor? Because of that comment, nothing is fixed right now, can you help us somehow?