6 PRINCIPLES OF ELECTRICAL DESIGN 



cost of labor. Provided the work is carefully done, the element 

 of time becomes, therefore, of the greatest importance. A 

 student in a technical school may be able to produce a neat and 

 correct drawing, but the salary he could earn as a draughtsman 

 in an engineering business might be very small because his rate 

 of working will be slow. The designer must always have in 

 mind the question of cost, not only material cost which is 

 fairly easy to estimate but also labor cost, which depends on 

 the size and complication of parts, accessibility of screws and 

 bolts, and similar factors. These things are rarely learned 

 thoroughly except by actual practice in engineering works, but 

 the student should try to realize their importance, and bear 

 them in mind. A study of design will do something toward 

 teaching a man the value of his time. Thus, although it is 

 important to check and countercheck all calculations, and time 

 so spent is rarely wasted, yet it is essential to know what degree 

 of approximation is allowable in the result. This is a matter of 

 judgment, or a sense of the absolute and relative importance of 

 things, which is developed only with practice. What is worth 

 doing, what is expedient, and what would be mere waste of time, 

 may be learned surely, if slowly, by the study and practice of 

 machine design. 



It is by taking on responsibilities that confidence and self- 

 reliance are developed; and the student may work out examples 

 in design by following his own methods, regardless of the par- 

 ticular practice advocated by a book or teacher. He can usually 

 check his results and satisfy himself that they are substantially 

 correct. This will give him far more encouragement and 

 satisfaction than the blind application of proven rules and for- 

 mulas. By making mistakes that are frequently due to 

 oversights or omissions and by having to go over the ground a 

 second or third time in order to rectify them, an important 

 lesson is learned, namely, that one must resist the tendency to 

 jump at conclusions. The necessity of checking one's work, 

 and proceeding systematically by doing at the right time and in 

 the right place the particular thing that should be done before 

 all others, is of great value in developing one of the most im- 

 portant qualifications of the engineer. This has already vaguely 

 been referred to as engineering judgment, a sense of proportion, 

 seeing the fitness of things; but all these are allied, if not actually 

 identical, with the one faculty of inestimable value known as 



