This is a fairly common situation: A 200 amp 480V meter/main w/breaker panel that needs to feed a 50 KVA stepdown transformer. The breaker lugs are rated down to #6 wire and the 100 amp primary protection fused disconnect lugs only accept up to #1/0 wire. Is there a good reason why there is not an exception in the tap rule that would allow feeding the disconnect from the breaker with #2 instead of having to go full sized and use pin terminals? A fused 200 amp meter/main solves the problem with 110 Amp fuses but they are not always available.
I may not be understanding you but if you are saying the 2ga conductors are protected by 100 a fuses on the load end, that sounds like a tap to me. You just need to follow the appropriate tap rules. I may be misunderstanding the question tho.
Greg, there are no provisions in the tap rules to feed a smaller wire from a breaker but you can feed a smaller wire from a feeder as a tap. It doesn't make sense that there is no provision in the code to allow feeding a smaller wire from a breaker than what the breaker is rated at.
The tap rules are basically saying a tap conductor can be protected at the load end at it's rated ampacity. You are describing a feeder tap. The issues are just that you need to follow the appropriate tap rules for the length and wiring method.
If this is 25' or less we use 240.21(B) (2) Taps Not over 7.5 m (25 ft) Long. Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following:
(1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.
OK it is half of the main
(2) The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side.
(3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
This is the open question, is it?
I agree the "tap" is actually the only load on the "feeder" but I don't see anything that prohibits that and it would be possible to add another load later.
If you have to go with full sized 3/0 wire, what are the options for termination at the 100 amp disconnect with only 1/0 lugs. Would the UL listing be compromised if you could find lugs bigger lugs that fit? Thanks for the input!
If there was any question you could put an inch or two of 3/0 and "tap" that with Polaris connectors but that only points out the silliness of trying to say this is not a legal tap.
Tap Conductors. As used in this article, a tap conductor is defined as a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.