Production Operators and Disconnects

[fraymond]

We have production machines that have moving gantry's. We have a 480 disconnect that removes power to the drives. The operator stops the machine. After locking out the disconnect, the operator attempts to operate the machine. After verification of no motion, the operator proceeds to enter the gantry zone/envelop to service the machine i.e. clean. Afterwards the LOTO is removed and the machine is placed back into service. My concern is the PPE level 0 that requires all cotton shirts. The operators are already wearing kevlar jackets with long sleeves and safety glasses. The above process happens 10+ times each shift. I am curious if other manufacturing facilities have similar concerns. Thanks for any responses.

 

[petersonra]

We have production machines that have moving gantry's. We have a 480 disconnect that removes power to the drives. The operator stops the machine. After locking out the disconnect, the operator attempts to operate the machine. After verification of no motion, the operator proceeds to enter the gantry zone/envelop to service the machine i.e. clean. Afterwards the LOTO is removed and the machine is placed back into service. My concern is the PPE level 0 that requires all cotton shirts. The operators are already wearing kevlar jackets with long sleeves and safety glasses. The above process happens 10+ times each shift. I am curious if other manufacturing facilities have similar concerns. Thanks for any responses.

PPE level 0 would seem to imply they are exposed to arc flash. Are they?

In any case, I think Kevlar jackets would qualify for level 0. Cotton is not the only material allowed. It is just the most common.

 

[fraymond]

Thanks Bob for the response. I am under the impression any electrical enclosure with a disconnect poses a potential arc flash hazard. As an example a direct short to ground when the disconnect is turned on.

 

[cdevine]

Arc flash is not really my area but given the number of isolations being performed are you comfortable that a try start is providing 100% accuracy, all of the time? For example could control circuit faults or interlocks be the reason for no operation on a try start rather than loss of power from the disconnect?

 

[petersonra]

Thanks Bob for the response. I am under the impression any electrical enclosure with a disconnect poses a potential arc flash hazard. As an example a direct short to ground when the disconnect is turned on.

I suspect that the arc would be confined to the inside of the disconnect enclosure if they have accurately classified it as HRC 0.

I am not saying this is the final word on such things, but it would seem to be a relatively low risk if properly classified.

 

[petersonra]

Arc flash is not really my area but given the number of isolations being performed are you comfortable that a try start is providing 100% accuracy, all of the time? For example could control circuit faults or interlocks be the reason for no operation on a try start rather than loss of power from the disconnect?

I have never quite understood the utility of trying to start a motor after you lock it out. All that proves is the control circuit at that point in time won't start the motor.

 

[pfalcon]

I suspect that the arc would be confined to the inside of the disconnect enclosure if they have accurately classified it as HRC 0.

I am not saying this is the final word on such things, but it would seem to be a relatively low risk if properly classified.

I have never quite understood the utility of trying to start a motor after you lock it out. All that proves is the control circuit at that point in time won't start the motor.

I agree on both counts.

Arc flash hazard is not created solely by using electrical power. It also requires exposure. Unless you're opening electrical equipment there's unlikely to be a call for the extra PPE. If your gantry uses an open buss then you need an EL to check the power before anyone else enters. If the LOTO disconnected the power then the extra PPE isn't called for.

Pushing motion buttons isn't sufficient to determine power loss for exposed electrical equipment.
As a point of fact all I do is work around, on, design, modify electrical equipment including gantries. I would never trust my life/fingers to testing lockout by pressing a motion button whether electricity was involved or not.
All that does is verify the program/wiring isn't expecting that pushbutton at that time. Maybe he forgot to set auto mode before pushing cycle start? Maybe it's all set to self-correct as soon as someone pushes that pallet back in position? brrrrrr

 

[Timbert]

NFPA 70e does not require all cotton shirts.

In any case, I think Kevlar jackets would qualify for level 0. Cotton is not the only material allowed. It is just the most common.

Kevlar would meet HRC 0 (if it is at least 4.5 oz/yd?) as it is non-melting.

NFPA 70e requires "protective clothing, nonmelting or untreated natural fiber with a fabric weight of at least 4.5 oz/yd?."

 

[cdevine]

Thanks pfalcon. To be fair, I think fraymond was referring to isolation for mechanical maintenance and therefor contact with parts that are sometimes energised, is not likely/impossible. On this basis most regulators accept verification without a live-dead-live check. My question was, given the frequency of isolation, is try-start really adequate in this case? Given the tone of the question you could guess that I am aligning with petersonra

I agree on both counts.

Pushing motion buttons isn't sufficient to determine power loss for exposed electrical equipment.
As a point of fact all I do is work around, on, design, modify electrical equipment including gantries. I would never trust my life/fingers to testing lockout by pressing a motion button whether electricity was involved or not.
All that does is verify the program/wiring isn't expecting that pushbutton at that time. Maybe he forgot to set auto mode before pushing cycle start? Maybe it's all set to self-correct as soon as someone pushes that pallet back in position? brrrrrr

 

[don_resqcapt19]

I have installed HOAs for this type of lockout verification. The hand position of the HOA directly operates the motor stater bypassing all interlocks, with the exception of the motor overloads. The lock out procedure is to put the HOA into the hand position and see the motor start, release the HOA (spring return to off), lockout the power disconnect, return to the HOA and put it into the hand position, if the motor does not start this time, the operator is free to do mechanical work on the equipment.

 

[cdevine]

I have installed HOAs for this type of lockout verification. The hand position of the HOA directly operates the motor stater bypassing all interlocks, with the exception of the motor overloads. The lock out procedure is to put the HOA into the hand position and see the motor start, release the HOA (spring return to off), lockout the power disconnect, return to the HOA and put it into the hand position, if the motor does not start this time, the operator is free to do mechanical work on the equipment.

Thanks don_resqcapt19. Certainly a more reliable solution. How do you accommodate the possibility of jammed equipment in your procedure?

 

[don_resqcapt19]

Thanks don_resqcapt19. Certainly a more reliable solution. How do you accommodate the possibility of jammed equipment in your procedure?

If the motor does not turn on the first try in hand, the operators have to put in a work order for maintenance to find out why it did not turn. The lockout procedure cannot go forward unless the motor turns on the first try in hand. The procedure is called, "try-lock-try".

 

[cdevine]

If the motor does not turn on the first try in hand, the operators have to put in a work order for maintenance to find out why it did not turn. The lockout procedure cannot go forward unless the motor turns on the first try in hand. The procedure is called, "try-lock-try".

Understood.

Do you ever get a situation where its just inconvenient to try start eg material on a conveyor belt, very large motors with limited starts per hour etc?

I assume execution of the work order could entail a live-dead-live check to address the jammed drive/inconvenient try start issues?

Is there a remote possibility of momentary loss of supply or intermittent fault following the first "try" start of the "try-lock-try" rendering the no-start result of the second "try" potentially misleading?

 

[don_resqcapt19]

Understood.

Do you ever get a situation where its just inconvenient to try start eg material on a conveyor belt, very large motors with limited starts per hour etc?

There can be issues the make it difficult for the try-lock-try method and they have to be addressed by policy and procedure on a case by case basis.

I assume execution of the work order could entail a live-dead-live check to address the jammed drive/inconvenient try start issues?

Yes, if you can't try the motor, then maintenance would use the live-dead-live method. This would be done at the remotely located motor starter as in most cases this plant does not have disconnects at each motor. Any time the verification of lockout is at a remote location, there is always a chance that the verification is not being done on the correct starter.

Is there a remote possibility of momentary loss of supply or intermittent fault following the first "try" start of the "try-lock-try" rendering the no-start result of the second "try" potentially misleading?

Sure, anything is possible, but with the hand position HOA bypassing all of the interlocks and the wire running directly to the motor starter, that is not a likely condition. The stater control power, in almost all cases in this plant, comes from a control power transformer in the motor stater.

All that being said, if the conditions permit it, the best method, in my opinion, is a local disconnect, installed where it is very clear what motor the disconnect feeds. Of course, you still have to be able to see or check the operation of the disconnect.

While on the expensive side, the Meltric plugs and receptacles at each motor provide a very visible "air break" of the power source. I also like the knife blade safety switches with the viewing window.

 

[cdevine]

Thanks don_resqcapt19.

One issue I have faced when talking to safety people is that isolation verification for mechanical works should be:

1. simple
2. the same on any electrical equipment
3. the same under any process conditions
4. accurate
5. inexpensive

Apparently, there is far more likelihood that verification will be performed and performed correctly if these conditions are met. In many cases, companies I know reverted to live-dead-live checks as isolation verification for mechanical works because they believed it ticked all of the above. Pretty soon they found that their electricians were fully utilised verifying isolations and not getting any electrical work done. They also started to find it quite expensive as operation and mechanical maintenance crews were doing a lot of waiting for the electrician to arrive. Nevertheless, they still liked live-dead-live verification because it ticked points 1 to 4 above. I got to thinking, what if a non electrician could perform the equivalent of a live-dead-live check? Answering that question has been a persistent topic for me for the last 10 years. That is why your first hand experience of solving the issue is very valuable to me and other forum readers.

Like you, I also see some merit in plug/socket and visible blade switches. However, I know most who have employed them would say that they fail on points 2 and 5 above! In some cases of visible blades I know that they have failed on points 1 and 4 as well!

It certainly is an interesting topic. Its no wonder company management struggles with this one.

 

[don_resqcapt19]

Thanks don_resqcapt19.

One issue I have faced when talking to safety people is that isolation verification for mechanical works should be:

1. simple
2. the same on any electrical equipment
3. the same under any process conditions
4. accurate
5. inexpensive

...

I am not sure that in a larger facility that you could satisfy points 2 and 3. I think there would almost always have some exceptions.

 

[cdevine]

I am not sure that in a larger facility that you could satisfy points 2 and 3. I think there would almost always have some exceptions.

Are you thinking that a live-dead-live check or similar could not be used on all electrical equipment and under any process condition? Please don't burst my bubble on this one!

Hang on, maybe you mean that any test, other than a live-dead-live check or similar, could not be used on all electrical equipment and under any process condition?

 

[GoldDigger]

And yet, the live-dead-live test does not conclusively prove that you opened the right disconnect. That part requires additional, often visual verification.
That particular assurance comes more authoritatively from try-lock-try, although that too has its limitations.

Tapatalk!

 

[don_resqcapt19]

Are you thinking that a live-dead-live check or similar could not be used on all electrical equipment and under any process condition? Please don't burst my bubble on this one!

How do you do that if the incident energy from a fault at that equipment is calculated to exceed 40 cal/cm??

You are in a catch 22, you have to verify that the power is off, but you have to wear PPE that is suitable for the incident energy if the power isn't off, but there is no PPE to protect you from incident energies that exceed 40 cal/cm?.

I guess my point is that in a plant of any size, it would be almost always be impossible to have a single method that will work with all of the equipment in the plant.

 

[don_resqcapt19]

And yet, the live-dead-live test does not conclusively prove that you opened the right disconnect. That part requires additional, often visual verification.
That particular assurance comes more authoritatively from try-lock-try, although that too has its limitations.

Tapatalk!

If the disconnect is not local to the equipment, how do you conclusively prove that the correct disconnect has been opened and locked out?