I have been trying to understand the application of the tap rules as set forth in the NEC, so I decided to open the handbook 70H. There is an example of the rule I am trying to understand in Fig 240.9 (taps < 25' to transformer primary). It is attached for reference.
Here's the problem I see with this diagram. First, the transformer is rated 37.5 kVA with FLA=45A primary. While the #8 can carry the 45A, it would make more sense to me to upsize the cable for better protection of the cable during overload conditions. Secondly, why is the fuse so large? 110A? That fuse is not protecting the trasnformer or the cable. I know the inrush can be high, but at 6 times FLA, the fuse would blow assuiming it is not a TD fuse. It just seems to me that the fuse disconnect is rated too high for this circuit. Am I missing something here?
Thanks.
Here's the problem I see with this diagram. First, the transformer is rated 37.5 kVA with FLA=45A primary. While the #8 can carry the 45A, it would make more sense to me to upsize the cable for better protection of the cable during overload conditions. Secondly, why is the fuse so large? 110A? That fuse is not protecting the trasnformer or the cable. I know the inrush can be high, but at 6 times FLA, the fuse would blow assuiming it is not a TD fuse. It just seems to me that the fuse disconnect is rated too high for this circuit. Am I missing something here?
Thanks.