Motor sudden start issue (unsafe)

[Jhonwyn01]

Greeting,
It happens that a big motor get started immediately after getting the permissive signal while the design is to have also the start command that has to be from Local switch only. So, both permissive and start are arranged in series at MCC for motor starting. The local switch signal (start)will go to DCS and then to the motor MCC through Modbus. same for permissive where signal to be through Modbus to the MCC. I have a safety concern if some body is working and by sudden motor get started while no body touch the start local switch.

Is it safe to have this design? and how about the standard calls.

Appreciate your help

 

[itsmoked]

If the latching function is indeed at the MCC and cannot actually occur without a human finger being involved then it's safe. If a human finger only signals the DCS and the DCS ultimately turns ON the motor then it would not be safe in a lot of situations.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

NO CONTROL INTERLOCK ALONE IS INHERENTLY SAFE WHEN WORKING ON A MACHINE!

If someone is working on a machine, you must have the POWER circuit disconnected, locked out and, in most safety procedure standards, tagged with information as to who is working on it and where. Here in North America, we call that a "Lock-Out / Tag-Out" (LO/TO) procedure.

That said, Keith's assessment on having manual device interaction could be said to be LESS UNSAFE than having no manual device interaction. But less unsafe is far from safe.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[FreddyNurk]

I agree with itsmoked. IEC62061 is but one of many standards that may well be relevant to such applications, but from the description, if Modbus is the protocol being used to ensure that a local operator is directly involved in the motor starting, I'd not want to be trusting it either.

 

[BrianPetersen]

jraef discussed the maintenance and lock-out situation, but even from the regular operator's perspective, if the starting of a motor can cause an unsafe condition, you have much bigger issues involved. You need to check the relevant machinery safety standards and apply the proper safeguarding measures, paying particular attention to protection from accidental start-up.

It is the maintenance person's responsibility to follow the proper lock-out procedure, it is the integrator's responsibility to ensure that the proper and compliant means of lock-out and information for use are provided (lockable disconnect switch with proper labelling and instructions), and it is the supervisor's responsibility to make sure their staff are following that procedure.

You should NOT be relying solely on non-safety-rated hardware and software, and you should NOT be relying solely on not having someone press a button, because people can and do press the wrong button at times.

 

[Jhonwyn01]

Thanks to all for the valuable input.
"Lock-Out / Tag-Out" (LO/TO) can be modified to cover this gap during work permit. However, the issue is when having such big motor as standby and get started due to wrong logic/signal while no body knows.

Is there any standard supporting the change if design to be hard wires instead of using Modbus.

 

[waross]

It is common in the industries that I work in for motors to start automatically from remote signals. The motors are guarded to prevent danger to workers. There may or may not be a local start button and if there is a local start button, it MAY only be active when a selector switch is changed to the local position.
LO/TO safety for work directly on the motor or machine is another issue, not to be confused with normal, automatic operation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BJC]

No one can answer your question without seeing the complete control schematic.
There may be two- The one that's on the drawing(S) and what actually exist. I would suggest verifying the drawings first. Have a verified "As built" drawing.
Verify the working operation of all components. All relays, axillary contacts etc should be shown on the drawings in the "shelf" position. Control switches need a development table.
You can't fix what's wrong till you know what you got.

 

[3DDave]

"However, the issue is when having such big motor as standby and get started due to wrong logic/signal while no body knows."

This is impossible to solve. You are asking how to prevent anything happening by mistake when there is a mistake.

The best you can do is to include interlocks to prevent the machine from running when people are in a position they can be injured. If those interlocks are wired wrong there is nothing to prevent injury. Even Lock-out/Tag-out has failed when the wrong circuit is opened and the electrician fails to check his work.

The next step is to have a schematic, review the schematic with other, experienced electrical workers, check the wiring that is installed matches the connections in the schematic, especially to avoid connections that should not be made. Make sure that switches on access panels are opened or closed by door operations as the schematic calls for, and that the correct voltages are seen on control signals -before- allowing the machine to be attached to power. If possible put a dummy load, such as a lamp, to indicate the status of power supplied to the motor(s) before the motors are connected.

I'm sure there are other, more complete checklists for equipment installation. It may be worthwhile to hire a plant-setup expert to handle this. They won't be familiar with the equipment and won't be mislead by expectations.