I presume the PLC is controlling other routes, thereby stopping all production instead of just one branch.
Of course, is the PLC point also the source of power to the motor, because if it isn't then perhaps you will need to lock out locally as well, after all.
In the end of the day all you can do is ensurer its safe for the engineer and do as told by management. If they lose production, then they will come around to the correct way of thinking eventually.
All motors are 480 VAC out of an MCC that the PLC controls. Locking out only the PLC will stop the motors, but it will not put them in a safe position.
Does the proposed proceedure call for both the disconnect and the PLC Panel to be Locked Out? I have seen this before and it is the lazy man's LOTO. If only the PLC, that would mean the motors were still operational from local controls at the switchgear. If the switch gear does not have local control, without LOTO, they could be jumpered or malfuction and still operate.
He's not sure if he wants both. There are no local controls for the motors. You are correct that the failure of a motor contactor will cause the motor to continue to run.
Bruce,
I feel your pain with the "safety guy" who wants to make something "totally safe" but does not know/ can not comprehend how their decision can cause more work and not really effect the overall safety of a given maintenance task, possibly making it less safe in some cases. My response to this situation has been to:
Lay out why the proposed additional “safety step” does not provide any additional real safety function.
Estimate the additional cost in time and then $ for doing it.
Sit down with the safety guy and have him explain it to me again why it’s needed.
If they are still adamant, ask them when they will have time to sit down with the plant manager to discuss these same points and rationally describe why we are wasting money to do them. Hopefully you will only have to do this once to show them you know what you are doing.
In your case, does the safety guy really want to sit down and explain to OSHA why an incident occurred due to their additional requirement(s)? The plant manager would also like to know what this answer will be. As always, CYA with sufficient paperwork so that you have a good case to prove your innocence if finger pointing occurs.
Mike
I really wish I could do this. Unfortunately, the higher management just told me to make it right and really didn't bother about anything else. They really don't want to get into a battle, they just want it done. As for the $$, it won't be seen until someone has to lock something out. Unfortunately, the rational part went out the window a while ago (at least for me). I really start to lose my patience around someone who acts like they know what they are doing but really has no clue.
It is my understanding that the LOTO requiements in NEC require that the lockout point be within sight of the motor. A local disconnect is most likely to meet that requirement. There are exceptions, but from a common sense standpoint you want to lock out the local disconnect so that you can't inadvertently operat a motor while you are testing the PLC, which must be done with power on at the PLC panel.
According to 430.102(B), the disconnecting means does not have to be in line of sight if it is lockable and in an idustrial installation where only qualified persons service the equipment - the exception you are probably referring to. I personally like the common sense approach. As for testing, the safety guy isn't concerned about our testing, just running the system.
In either case, ours is within 5 feet of the motor, labled and lockable.
brucechase, I'm not 100% sure from your post if you mean the safety guy wants to lock out the plc cabinet in addition to or instead of the local disconnect. If "in addition to" then I would probably let this guy have his way and move on with life. As long as your procedures indiucate you need to lock out the local disconnect the added disconnect at the PLC cabinet doesn't make this any less safe.
If "instead of" alot depends on cabinet placement and power feeds. As Tom said the lockout point needs to be in site of the item being worked on. In addition you need to lock out the primary power source. We do alot of smaller machies. The control cabinets are usually right next to the machine. So we have a single lockable disconnect on the cabinet to cover the whole machine. But that disconnect removes motor power n addition to control power. Tom makes the good point that this may not be logistically optimal from a testing standpoint. But it satisfies the safety requirements.
If the plc cabinet lockout only drops the control system and does not isolate the power system I don't consider that a reliable lockout at all.
Keith
I agree and wish I could just let him have his way. My only problem comes in the fact that I've seen people cut off the PLC disconnect and watch all the motors stop. It's not a far stretch for them to think that this is an acceptable lockout point (especially if it is labled with a "LOCKOUT HERE" sticker).
We have a lot of machines in which the disconnect does isolate the motor power along with the PLC. I'm more worried about the confusion that can happen if the disconnect is labeled like a machine disconnect.
Unless we are talking safety PLC here, then what the PLC does or does not shall be totally irrelevant for the safety.
If the 'safety guy' is insecure if the safety measures are good enough, then he should not try to improve the safety measures by using the PLC as a safety device. In stead he must improve the real safety measures, or verify that the current measures are good enough.
A common disconnect that shuts down an entire plant is possible (in stead of a PLC shutting down an entire plant), but consider that safety measures must be reasonable and not hindering or limiting the operation of the plant in an unjustifiable way. If the safety measures are too draconian, then operators may be tempted to bypass them to avoid other problems, such as lost production. Because of this a local individual disconnect per device or machine is the norm.
For vey large devices or motors, a local disconnect may not be possible. In that case Lock-out and Tag-out in a central distribution panel for example is acceptable.
You need to make sure that labeling in the field of both devices and disconnects is good enough.
And make sure that there are instructions.
The instructions shall include advice about what to disconnect. If other devices are relevant, then state that they must be disconnected as well. A list detailing each device is a good idea (i.e. "For work on conveyor 23, disconnect conveyors 22, 23, 24 and 25").
And make sure that the maintenance personnel has read and understood the instructions (have them sign a declaration stating that they have).
It is quite simple really.
No safety PLC here, just an AB 5/05. You are right about people trying to bypass things to make their life easier (or just to make production run). I wouldn't want someone to lose their life because of it though. As for labeling, all my systems are color coded and labeled at both the disconnect and the MCC. I try to make it as dummy proof as possible, but there are some smart dummies out there.
Locking out the PLC is not the answer, you need to isolate the power to the motor either at a local disconnect or back at the MCC.
The local disconnect does you no good if you want to work on the electrical items.
Typically the electrical supply for pull switches, missalignment etc is supplied from the motor starter.
If you lock out the PLC it will make it very dificult for maintenance.
Roy
Yes, it will make it difficult if the PLC has to be locked out. Our control power is seperate from the motor starter in our system. The control panel supplies all the voltages for all the controls and field devices.
All in all, I appreciate the good suggestions from everyone. My problem is I've started to let my lack of patience get in the way and now battle lines are being drawn. I've never wanted something like this to happen because safety should not be a political game. I just wanted a non-confusing system that is easy to operate and easy to isolate when working on it.
Thanks for letting me vent a little.