[wizard]

Good info Al.

Have you noticed safety relays being the heaviest maintenance item in modern control panels? Maybe semi modern. Maybe it is the implementation of the specifier but I have machines that all electrical failures over the years, inside the control panel, have been safety relays.

While on the subject of safety, this is what NFPA79 has to say about E--stop, at least as far as N.A. is concerned.
The electrical code allows for a controlled stop, where the controlled stopping of a VFD can be done according to code using a Safety Relay, these can be obtained with all kinds of features such as issuing a stop input to the VFD PLC input followed by a disconnect via the supply contactor.
Safety relays are typically one device that can achieve this and have been in used on European machines for some years, they are slowly becoming more popular and eventually mandatory for N.A.

The E-Stop process required by industrial machinery is spelled out in NFPA79 (Electrical Standard for Industrial Control).
There are three categories of stop outlined, 0,1 & 2.
Cat 0: Is stopping by immediate removal of power to the whole machine, i.e. an uncontrolled stop.
Cat 1: A controlled stop with power to the machine actuators available in order to achieve a the stop and then power removed, the controlled stop is where a Cat: 0 may cause damage to both machine and personnel.
Cat 2: Basically is a the same as Cat1 but power is left on to actuators such as input devices such as PLC inputs etc which will still allow monitoring their current state.
Al.