M-T-M and Tap Rule
- Thread starter liverpool
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Ratings of ocpd's, bus, switchboard, and any other pertinent equipment not mentioned...???
You can only have a tap situation if something is undersized for the ocpd supplying it.
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So if my tie OCPD matches the tie busway, then it is not a tap situation by definition? What section of the NEC made you come to this conclusion?
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If the two main breakers, the tie breaker and the tie bus all have the same current rating, then it is hard to see where a tap could come into play, but I can see some inspector considering that the tie bus could be fed from both ends simultaneously and have a load attached to the tie bus which would then be able to draw twice the rated current. But any individual cross section of the bus would still never see more than the current coming from one side.
Similarly, he could argue that the buses in each main load panels could be fed twice the current of the main breaker because it could be the sum of the main and tie current. But that would not be a tap situation, just a lack of protection.
Similarly, he could argue that the buses in each main load panels could be fed twice the current of the main breaker because it could be the sum of the main and tie current. But that would not be a tap situation, just a lack of protection.
GD covered the "physics".
The definition of tap conductors is in 240.2.
If not tap conductors by definition, the only other requirements I can think of offhand would be 450.6 Secondary Ties, and that would only apply if each main is fed by a different transformer.
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