E-Stops

[kolyur]

Most newer drives (less than 3 years old) have a safe off option which isolates the IGBT's from the motor circuit and is not damaging to drive components and is rated to safty level of SIL 3. This trumps the need for a isolation contactor.

This is a nice feature on newer drives. What I've done in the past on machines we build is to use a safety relay with immediate and off-delayed contacts. The immediate contacts act as your MCR and drop power to the PLC outputs when the E-stop is triggered (thus disabling and ramping down servos and VFDs). The delayed contacts control contactors which are located on the load side of the drives (interruping the motor). These drop out about 1 second later to create a safe condition without stressing the drive electronics.

Concerning OEM machinery that we purchase, I have seen many instances where either (1) the MCR just kills the enable signal to the drive, without any mechanical interlock, or (2) the MCR shuts off a contactor on the line side of the drive, dropping power to the entire unit. Both of these setups drive me nuts because (1) isn't safe in many cases and (2) can be bad for the drive. Many drives I've worked with (esp. servos) warn you in the manual that line power should not be cycled on a regular basis.

But my master electrician said it should kill all control power and the machines outputs by code.

I have yet to find any U.S. regulations that dictate this. I am not a safety standards expert by any means, but the codes I have read are extremely vague about specific wiring requirements unless you are dealing with certain types of equipment like punch presses.

 

[shooter]

E stop It should stop a dangerous situation>
The IEC says as first you must use breakers in the main circuit to dangerous equipment (and manual switches too to switch off fans for example.
There are safety PLC blocks you can use however your program must be able to check the position they are in.
Estop does not mean the control voltage has to be stopped, only motions and energies. On hydraulic machines it means the buffer has to be flushed.
This only when it is not necesary to open a press for example when somebody could be in it.
E stop means you need a safe situation, sometimes it means stop everything, sometimes it means reverse a motion.
An estop is not allowed to be inside the program, as you can not be sure the program is running.
Best way in difficult sits is to use a separate PLC dedicated to the safety.