Services - Transformer Secondary Overcurrent Protection

[ryanee26]

I have come across a situation where I need some advice to make sure I'm not crazy, or confirm that I am. Say a building is served from a single utility transformer, 500kVA 12.47kV:480/277V for example. This building is comprised of 2 separate tenants, each with it's own meter and service disconnect outside (circuit breaker type). If a third tenant wishes to move in and requires a third meter and service disconnect, does NEC article 450 on transformer secondary protection apply (a maximum of 6 overcurrent devices are allowed with a total rating sum not more than 125% FLA-Table 450.3(B) assuming primary protection and secondary less than 600V)? I cannot find in Article 230 a maximum rating of overcurrent devices for a service, just the mention that it cannot be more than 6 total disconnects. 230.79 simply states that the service disconnect rating must equal the load being carried, and 230.80 seems to state that the sum of the ratings can be any number as long as it meets the minimum stated in 230.79. If 450 does not apply because the utility can do whatever it wants with it's own xfmrs, and since the referenced articles from 230 above seem to separate services from other xfmr installations, why do some of the permitting folks I deal with state that the overcurrent protection in that situation violates Article 450? Are they just not interpreting it correctly?

 

[wareagle]

The NEC does not apply to the utiltiy. You need not be concerned regarding Table 450.3B. If the load is too much the utility will just add a bigger unit. You are required to only have a max of 6 disconnects. There is no maximum rating for these disconnects.