Hey, guys. I've been reading a number of previous posts on the subject and have reviewed the code book, but still am unclear about a few things. When (under what circumstances) am I able to use the 250% rule for primary protection? When can I use primary overcurrent protection only to protect both the primary and secondary of the transformer? Table 450.3(B) indicates that secondary protection is not required for transformers rated 9 or more amps with up to 125% protection of the primary, yet secondary protection of conductors is almost always necessary according to 240.21(C). Just hoping for some clarification on this, as I'm studying for my master's exam. Thanks.