In the US, almost all technical exams on electrical works are based on the National Electrical Code NEC. However, the NEC book itself is a 1500+ pages mega size monster. You just won't have the time and energy to go through and memorize everything in there. Even though the exams may allow you to use the code book, looking up a particular item can be very time consuming and you may run out of time real quick This is why we come up with this study product - we provide you with essential knowledge and information that can be easily comprehended so that during the actual exams you won't need to browse the code book for answering every single question Officially, the N17 exam covers these: General Knowledge Services and Service Equipment Feeders Branch Circuits and Conductors Wiring Methods and Materials Equipment and Devices Control Devices Motors and Generators Special Occupancies, Equipment, and Conditions The N18 exam covers these: General Knowledge Services and Service Equipment Feeders Branch Circuits and Conductors Wiring Methods and Materials Equipment and Devices Special Occupancies, Equipment, and Conditions And the N19 exam covers these: General Knowledge and Calculations Utilization Equipment and Devices Motors and Controls Wiring Methods, Materials, and Conductors Grounding and Overcurrent Protection Special Occupancies, Systems, and Equipment As you can see, these exams share so many common knowledge items that it would be wise to group the study material together. In any case, the exams require that you have a working grasp of the NEC. There is no way you can pass the exams without having solid real world experience. Our notes give you knowledge, principles and concepts. To master the topics, you must be "in the field". And you need to know how the experts get things done. To succeed in the exam, you also need to read as many reference books as possible.