Design Reference Sources (NFPA, NEC Codes & Standards)


Joined Jul 18, 2013
The E-Stop for a machine has 3 options, one is to disconnect ALL motive force driven items, the second is a controlled stop such as where the immediate removal of power will, or can, cause damage to personnel or machine.
I believe they are rated type 0,1 & 2.
This is where you would pick the correct version of the safety relay etc, that can give you a choice of options.
BTW it is customary to retain power to the central controller and all inputs, output power is usually terminated.
This allows some degree of trouble shooting, monitoring of PLC screen for e.g. etc.


Joined Mar 19, 2019
I also had a couple of other reference books that I relied on for industrial designs dealing with electrical equipment. Both were circa 1940s and still pertinent. Mark's Mechanical Engineering Handbook and the AISC (American Institute of Steel Construction) Steel Handbook. Both timeless and easily obtained used. For example, designing steel stanchions for area lighting fixture supports in Hurricane rated wind loads. Designing mounting frames for large steel NEMA 4R control boxes, etc. All the material specs and various formulas for moments of inertia and such.


Joined Jul 18, 2013
@maitrey Not sure if your equipment uses motors of any significant size, but one thing to be aware of if using the Schnieder schematics for a reference, is what is now one minor practice considered bad design, and that is where a standard motor overload is used, the contact to drop the coil out was used on the return or neutral side of the coil.
It is now considered correct practice to move this to the other side of the coil in the ladder rung with the other functions.
I generally use the other O/L contact generally N.O. as a monitor or indication in the ladder.