Another vote for the FX-115ES. I passed my FE and PE exams with it first try. It's definitely a time saver on certain problems that would otherwise require multiple calculations using other calculators.
GE Transformer Protection Reference
Instrumentation Transformers Application Guide by ABB
Selective Coordination Handout by Bussmann
Article on types of Ground Fault Protection by Jim Rasmussen, GE Specification Engineer
Resistance Grounding System Basics by Michael D. Seal
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I probably put in a total of about 4-500 hours of studying. The biggest thing is to stay organized and know exactly where to go for your materials. I had 3 binders that I used for about 80% of the test. One has all of the typical power subjects in it (3 phase, delta/wye, complex power...