PLC and Drive Panel Safety

[acerfootball]

First off, I'm am extremely impressed with the content on this forum. This will definitely be my go to with electrical safety questions in the future.

With that said, I'm still learning the ins and outs of 70E and have a question regarding the maintenance with drive and PLC panels. We build custom automated machinery that always have multiple drive panels and at least one plc panel. Our technicians often are opening these panels and connecting via Ethernet to make changes to the code. These machines are meant to run continuously so shutting down these panels is never preferred. But my thinking is that according to 70E they need to be since once the panel door is open the technician will be exposed to live bus bar or live dim rails. The PLC usually run on 24 VDC so we might be good there but the drive panels have 480. Am I reading the code correctly when I say that unless an energized work permit is obtained those panels need to be put in a safe working condition (or denergized) in order for anyone to open them up?

Thanks in advance!

 

[fmtjfw]

BEGINNING OF RANT

BEGINNING OF RANT

If the DIN rails are live then you have a big grounding failure:huh:

Is the HAZARD of working the panel live less than the hazard to people's life or physical injury when they are turned off? Is the boss willing to work them live? Is he a Qualified Person? Does he know the hazards and how to avoid them?

Or is this just a matter of money?

END OF RANT

Why aren't the Ethernet connections outside the panel? A short length of cable and another jack should cost about $10 max.

 

[petersonra]

There are two separate hazards involved. one is shock and the other is arc flash.

You have to protect employees from both hazards.

De-energization protects from both hazards.

Shock can be protected from by either distance or PPE including appropriately rated insulated gloves.

Arc flash is protected from by either distance or appropriate PPE.

You can't as a practical matter reprogram anything with the power off, and it is most of the time more or less a debugging exercise so you are permitted under NFPA70e to engage in this activity if done in a safe way with the power on, IMO.

In some cases it is possible to arrange equipment inside the cabinet so there is no hazard that the employee is exposed to by plugging in a communications cable.

having said that, it is much simpler and safer to just put a bulkhead connector on the door of the enclosure so you do not have open the door to communicate electronically with the devices inside.

A Graceport or similar device is a common solution. They can be as much as several hundred dollars each though, depending on exact configuration.
http://graceport.com/graceports/top-ten-graceport-configurations

 

[cornbread]

Using a laptop to the PLC is normal troubleshooting in my humble opinion. In cabinets that have 480V mixed in with the PLC's we have done arc flash studies and use the PPE required. Typically its the same as opening a 480V MCC bucket. It's a royal pane in the butt, can't deny its safe. If I were designing a cabinet... the 480V would be isolated in its own enclosure..or vise versa the controls in a sperate cabinet. The door ports are nice, however I like looking at the I/O as my 1st line of troubleshooting... if I have to open the door I must don my PPE.

 

[Jraef]

Ironic that the drives program via Ethernet, because Ethernet allows for remote programming, as in not even in the same room. That is the absolute safest environment now, because even with the doors closed on the drive cabinet, there is still some risk of getting hurt if there is an arc flash. You can get VFDs in Arc Resistant MCCs with drives in them, but the size is limited. At some point the need for ventilation of the drive surpasses the ability to contain the arc blast pressure.

 

[pfalcon]

Using a laptop to the PLC is normal troubleshooting in my humble opinion. In cabinets that have 480V mixed in with the PLC's we have done arc flash studies and use the PPE required. Typically its the same as opening a 480V MCC bucket. It's a royal pane in the butt, can't deny its safe. If I were designing a cabinet... the 480V would be isolated in its own enclosure..or vise versa the controls in a sperate cabinet. The door ports are nice, however I like looking at the I/O as my 1st line of troubleshooting... if I have to open the door I must don my PPE.

Yep.

Ironically if you put all the 480/120 loads in one cabinet and all the 24 controls in a separate cabinet then the NFPA79 still says the controls cabinet has to be interlocked to the power cabinet :doh:

We now require I/O displays for our HMI. They can place a pretty machine layout with appropriately located lights if they like. Or they can provide I/O lists which I often prefer. But each indicator is for one and only one I/O point and shows the unconditioned state - just like the light on the I/O card. Through panel port connectors are required so we can plug the laptop.

If the job's too small for all that stuff then I go with a Proface LT or the like. Built in ladder display, color touch screen, USB/Thumb drive programmable. Stick in an I/O indicator screen and I'm all set.

 

[meternerd]

Maybe this is a silly question, but...when you change the programming of a PLC, don't you have the equipment stopped anyway? Isn't that pretty close to a shutdown? I don't know of any PLC's that allow reprogramming while in the run mode. If the PLC is powered by the 480/120 control transformer, as many are, and the PLC is in with the 480, then you'd still have a shock potential. Cover or arc flash PPE might be a good idea, but I don't think it's required. At least we never used it. Just wore FR clothing unless we were actually working on the 480. Maybe it's just company policy. We are only required to wear the level 3 arc flash suit if removing a bolted cover on 480, not just opening the door.

 

[petersonra]

Maybe this is a silly question, but...when you change the programming of a PLC, don't you have the equipment stopped anyway? Isn't that pretty close to a shutdown? I don't know of any PLC's that allow reprogramming while in the run mode. If the PLC is powered by the 480/120 control transformer, as many are, and the PLC is in with the 480, then you'd still have a shock potential. Cover or arc flash PPE might be a good idea, but I don't think it's required. At least we never used it. Just wore FR clothing unless we were actually working on the 480. Maybe it's just company policy. We are only required to wear the level 3 arc flash suit if removing a bolted cover on 480, not just opening the door.

Most PLCs these days can be programmed on the fly. It is not always the best of ideas, especially for those who might not be the swiftest of programmers, but it be done and is pretty routine.