8 PLC Safety Precautions for Electrical Engineers

Hello Programmers,

Are you ready to start the logic development of your new process or machine, just wait?

You may be prepared with your auto sequence, logic discussion, interlocks, alarms, user management, etc.

Am I right?

I think absolutely ‘Yes’. Because, every PLC programmer starts with this stuff. But, today I am going to tell you about one more thing which you must consider prior to start programming that is safety, safety, and safety.

Every machine or every process must be safety proof with mechanical safeties as well as electrical and electronics safeties.

While programming one should consider all the safeties regarding electrical and fail-safe conditions.

Important PLC Safety Tips for Automation Programmers and Engineers

Here let’s have look at some of the safety considerations.

  1. Every system should have emergency switches and it should be connected in ‘NC connections’. In the PLC program, the emergency switch should be in interlock with all outputs (like motor, pumps, solenoids valves, contractors, etc.) and it should be resume with acknowledgment of the same. All actions should be stopped with emergency switches. All emergency switches should be easily accessible to all operators. For the number of operators, there should be a number of emergency switches.
  2. All conveyor systems or material handling systems should be safety-proof with over travel switches and it should be also in ‘NC connections’ and the same should be interlocked with related conveyors to avoid any accident.
  3. Do you like to write ladder logic programming with set-reset instructions then you must not forget to reset the bits on safety calls? All set bits which give the command to output should be reset with all safety switches, emergency switches, and in manual conditions.
  4. Always remember that do not bypass any safety in manual actions also because an accident can happen in both auto and manual.
  5. Experienced programmers always follow safety regulations and that’s why everyone demands experienced people. So being a PLC programmer you must think about multiple fail-safe conditions and interlocks.
  6. For press machine’s you must have a covered scenario or light curtain, While wiring light curtain to PLC always makes ‘NC connection’ for additional PLC safety of wire break. And in the programing part interlock it with down action output.
  7. Alarms! Your program must contain multiple alarms like the motor trip, over travel, cylinder stuck, the sensor fails, over travel, the sensor fails, emergency activated, main power failure, phase missing, safety curtain break, MCB or MCCB or MPCB tripped, overcurrent, under-voltage or overvoltage, high pressure, low pressure, high temperature, and low temperature, etc.
  8. If you are programming in process or oil and gas domain then you should take many precautions in the program, these domains cannot afford any mistake of PLC programmer and your minor safety bypass could lead to major accidents. So while programming in this domain always makes the list of all safety valves, safety alarms, safety conditions, and interlocks.

All these safety precautions are applicable for all the standard PLC brands like Siemens, ABB, AB (or Rockwell), Omron, Beckhoff, Mitsubishi, pluto, Schneider, profisafe PLCs, etc.

Always have a discussion about PLC safety points with the process owner or process designer.

Friends, Thank you for the reading. These are some of the key safety points for PLC programmers, you can find much more like this. Be safe!

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