E-Stop Push-Button Implementation ???

[86ed]

Hello Everyone,

I wanted to get some direction or possible opinions regarding the electrical implementation of “E-Stop” push-buttons used in process related systems (for example a pump that is performing process “X” which is being driven by a medium voltage motor fed from a MV controller). In this case the process is being controlled and monitored by a local PLC--–start and stop commands from the PLC are wired directly to MV controller open and close circuits. In the case of an emergency you would want to wire contacts from the E-Stop push button directly to the MV controller trip circuit AND to the PLC (the PLC can then issue a back-up stop command for example)--right? Are there any codes or standards that would dictate proper implementation of E-Stop circuits that would be related to a process “X”? Or is the philosophy more of an industry best practice issue that is not really governed by codes and standards?

Thanks guys….

 

[jraef]

No code or standard requires you to use an "E-Stop" button at all, so how you use it is up to you. It is also highly dependent upon your process, control system and safety protocol for the operators in the plant. No generalization can help you here, it's going to take "ICD"; Investigation of your equipment and situation, Communication with all of the stakeholders, and Documentation of your decision making process.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[rbalex]

There are a few operations such as motor fuel dispensing (NEC Art 514) and Elevators (NEC Art 620) that do require emergency shutdowns; however, other than being "reliable" there are no specifications for implementation.

For process control you might want to consider API RP 540. It is neither a Code nor Standard but it is an ANSI sanctioned recommended practice. ISA also has several documents that address the issue.

 

[leur2011]

The emergency stop pushbutton is a mandatory requirement of NFPA 79, read section 10 of the code and it will tell the location, mounting height, accessibility, and its purpose. The main purpose of the RED mushroom emergency stop pushbutton is the safety of maintenance personnel and to minimize the possibility of damage of equipments.

The emergency stop pushbutton SHALL be DIRECTLY wired in series to the coil of the motor control within the medium voltage controlgear such that it will simultaneously dropped all the contactor contacts INSTANTLY, and override all the command from the solid state devices, e.g. DCS or PLC.

NEC NFPA 70 mandated the motor local control station STOP / START pushbutton must be directly wired in series with the coil of the motor starter.

In my experience, I have seen medium voltage motors that have been damage because thay are hardwired directly to the DCS or PLC which has corrupted programs/software, and wrong configurations.