Teacher needs help with Motor Controls

[tim_callinan]

Hello Folks,

I'm an instructor at a community college and have greatly valued the advice I've received from this group in the past. I find myself in need of your expertise once again. My area of instruction is mechatronics, and while I'm comfortable with smaller motors like stepper and servo motors, AC motor control, particularly with high voltages, is not my forte. I'm particularly concerned about ensuring the safety of my students while working with our lab equipment.

I've attached photos of the training setups used by my students, which include VFDs, motor starters, relays, and 3-phase motors housed in cabinets. During labs, students work in pairs on either side of a double-sided trainer to build circuits from schematics I provide, but tests are conducted only under my direct supervision. Our lab is powered by 208V three-phase electricity, and all enclosures are grounded, with disconnect switches and LOTO procedures in place.

However, there are challenges, especially when troubleshooting is needed. Ideally, students would be more involved in this process, but that would require them to work on live cabinets, raising safety concerns. Additionally, there are times I need to use a meter to check circuit voltages.

With this context, I have a few questions:

Is it advisable for me to wear electrical gloves while probing live circuits?
My students need to adjust VFD parameters directly on the control panel, which involves interacting with a live part of the VFD. Is this safe, or are there better practices we should follow?
I would appreciate any safety recommendations you might have after reviewing the photos of our lab setup.
Thank you all for your continued support and guidance over the years. It has been invaluable to me as an instructor.

Best regards,
Tim

 

[icky812]

Most of those devices are finger safe. Unless you are running 480V equipment, electricity is a self teaching discipline. They'll only touch it once. With that said, if the students are under 18, you should be sending home a liability waiver for parents to sign. And yes proper PPE should always be worn. Safety Glasses, Gloves, Long Sleeve shirts, etc.

Personally I'd be a lot more worried about those live motor shaft ends that are not covered. That's a direct OSHA violation and a much bigger hazard. Get a finger ripped off or hair wound up in it and someone is going to have a really bad day.

 

[tim_callinan]

Hi icky812,
Thanks for the reply. Good advice. We do get them to sign waivers. But when you are working in cabinet with a multimeter and 208 is the max voltage - do you use gloves? Do you have a shield? Ill be honest - it seems overkill to me but that's why Im asking.
My students use the Powerflex 525 - they wire up the high power terminals in the bottom. For example, one of the three phase supplies could come out by accident and make contact with students arm as they are programming the VFD parameters. Obviously this would not be good.
If they had to wear gloves - this wouldnt be the worst thing. Do they have enough dexterity to be able to program a VFD? I suppose Ill find out.
Tim

 

[robertmee]

Hi icky812,
Thanks for the reply. Good advice. We do get them to sign waivers. But when you are working in cabinet with a multimeter and 208 is the max voltage - do you use gloves? Do you have a shield? Ill be honest - it seems overkill to me but that's why Im asking.
My students use the Powerflex 525 - they wire up the high power terminals in the bottom. For example, one of the three phase supplies could come out by accident and make contact with students arm as they are programming the VFD parameters. Obviously this would not be good.
If they had to wear gloves - this wouldnt be the worst thing. Do they have enough dexterity to be able to program a VFD? I suppose Ill find out.
Tim

For Arc Flash reasons and safety, any entry into a live panel, they should be wearing non conductive gloves and safety glasses at a minimum. However, if the worry is about programming the drive, the solution is simple. Purchase a remote HIM 22-HIM-A3 for the drive and mount it on the door. Then the drive can be operated safely. You can find them used for a few hundred $.

 

[Puddle]

Purchase a remote HIM 22-HIM-A3 for the drive and mount it on the door. Then the drive can be operated safely. You can find them used for a few hundred $.

I was going to suggest that, but once again the price of something with an Allen Bradley logo on it has shocked me. I'm used to Siemens world where that would be £50!

I've also been on courses where the test motor has the drive end guarded by perspex and has a round attachment with black and yellow quadrants marked, which makes it easily visible when running. I haven't been able to find an example on Google though, any search for "motor" and "quadrants" assumes I'm looking for something completely different.

 

[(8{)} ( .)]

The 1st thing that comes to mind is that this would be a great opportunity to teach LOTO.

 

[BryanG]

Many many many many years ago when I was in a college they had Earth Leakage protection for everything. I think them thar folk over the Atlantic call it ground fault circuit detection. You still get trained to be careful, but if it does all go wrong, nobody gets hurt. My Dad's advice was to always have one hand in your pocket, you need two points of contact for a current to flow, though I never did understand how you were going to use a multimeter with only one hand. Using insulating floor mats stops electricity going through your shoes. As I say, it was a long time ago in the UK and advice may have changed.

 

[robertmee]

Many many many many years ago when I was in a college they had Earth Leakage protection for everything. I think them thar folk over the Atlantic call it ground fault circuit detection. You still get trained to be careful, but if it does all go wrong, nobody gets hurt. My Dad's advice was to always have one hand in your pocket, you need two points of contact for a current to flow, though I never did understand how you were going to use a multimeter with only one hand. Using insulating floor mats stops electricity going through your shoes. As I say, it was a long time ago in the UK and advice may have changed.

Reminds me of a story about an old school electrician and his apprentice. The old school guy used to check for live circuits in a panelboard without a meter, by touching his pointer and pinkie finger on the same hand across a circuit. Mild tingle, but current through the hand as long as not touching anything else and standing on rubber shoes. His apprentice saw this and tried to mimick it, but missed one detail. He used his pointer fingers from both hands. That's current through the heart.

 

[(8{)} ( .)]

Reminds me of a story about an old school electrician and his apprentice. The old school guy used to check for live circuits in a panelboard without a meter, by touching his pointer and pinkie finger on the same hand across a circuit. Mild tingle, but current through the hand as long as not touching anything else and standing on rubber shoes. His apprentice saw this and tried to mimick it, but missed one detail. He used his pointer fingers from both hands. That's current through the heart.

Reminds me when I was a young electrician working in a chemical plant. I was standing behind the senior electrician when a VSD exploded. After blinking for a few seconds I noticed that a spark hit square in the middle of my right glasses lens. You can never be too careful with this stuff.

 

[arpus4KM]

My opinion as someone who probably spends way too much time in a cabinet without PPE.... because we all do.


Certain people make me nervous when in a cabinet, these are the people that have a lack of knowledge of what they are touching. These days I take my ring off and put it in my watch pocket in my jeans (the little pocket inside the right side pocket nobody uses, but is still there) and I put on safety glasses no matter what, because it doesn't take but a tiny fragment of molten copper or plastic to knock an eye out of commission.

Do I wear gloves in a cabinet.....No, But i'm also very conscious of where my fingers are, I don't grab live components, or use my finger to probe for loose wires. I typically have a 1000v screwdriver or 1000v pliers to touch terminals and contactors for testing. Not 100% of the time though because all cabinets are different.



What makes me nervous is when somebody is clearly 1/8" from a live 277v line while resting the other hand on the cabinet door, and when you remind them it''s a live cabinet, they kind of shrug and go "yeah, i got it". But you turn back and they are just about to put their meter in Ohms and stick it across a live fuse (to which it didn't blow, because the fuse wasn't blown thankfully).


What would I suggest for a class full of ignorant kids after having taught a bunch of fresh community college work program kids that were 18-20 at the time?

Safety glasses all the time, not because they are going to get dust, dirt, or a nail in their eye. Explain that they can easily lose an eye if even a 110v wire grounds out and goes molten. one POP, and that piece is naturally attracted to a cornea for some reason.

Gloves, Get them used to working with 1000v insulated gloves and protectors because the safety standards are going up and new plants are requiring these things. Link below
https://www.zoro.com/salisbury-electrical-rubber-glove-kit-leather-protectors-glove-bag-red-11-in-class-0-size-9-1-pair-gk011r9/i/G0032444/?utm_source=google&utm_medium=surfaces&utm_campaign=shopping%20feed&utm_content=free%20google%20shopping%20clicks&campaignid=20749401279&productid=G0032444&v=&gad_source=1&gclid=Cj0KCQiA5rGuBhCnARIsAN11vgTLv7iGwc_EYomAW6ii2tMUd7sa73QuEsNfXWrrFQ_oWHE8josgx_oaAo29EALw_wcB&gclsrc=aw.ds They should really only need to wear these gloves if they are working in a live cabinet, where they are going to be touching any wires or devices that aren't meant to be touched live. I don't think i would worry if they had to program a drive.


I assume you are already having them wear cotton clothes only while in the shop? I would make sure they are, or have some cotton work smocks they can wear so an errant molten particle doesn't melt their shirt to their skin if someone messes up.


I would also teach proper body position when dealing with a machine or cabinet you are unfamiliar with. Hands behind your back, or in your pocket. don't touch to show someone something, use laser pointers if you need to express a specific terminal to avoid touching. Anything to teach them not to touch and lean on things that are live. Been around a lot of guys that got small and big shocks by leaning and touching without looking.


Also. Cut off or cover the motor shafts on those motors! The temptation for a teenager to touch a running motor shaft is akin to putting a sign near a dark hole in the wall that says "Don't look in this hole".... They are going to do it out of a morbid curiosity or dumb dare.






It's a class full of people who don't know what they are doing for the most part and are trying to learn. There are going to be mistakes. Try to take precautions that are tailored to an environment like that.

 

[arpus4KM]

Hi icky812,
Thanks for the reply. Good advice. We do get them to sign waivers. But when you are working in cabinet with a multimeter and 208 is the max voltage - do you use gloves? Do you have a shield? Ill be honest - it seems overkill to me but that's why Im asking.
My students use the Powerflex 525 - they wire up the high power terminals in the bottom. For example, one of the three phase supplies could come out by accident and make contact with students arm as they are programming the VFD parameters. Obviously this would not be good.
If they had to wear gloves - this wouldnt be the worst thing. Do they have enough dexterity to be able to program a VFD? I suppose Ill find out.
Tim

If it's a powerflex 525, any laptop running connected components will get you remote programming ability. you could also teach them how to program before powerup by taking the face off and using the USB utility on it.

All these are good to know how to do when buttons aren't accessible on the drive itself.

 

[kekrahulik]

Let me throw out this story.

I had a cabinet with drives in it. The 480 came into the cabinet to a breaker that fed power to a distribution block, which fed the fuses to the drives.

One day while the line was down, we changed a few drive parameters (no tools used, nothing touched but HIM modules) and then downloaded a new PLC program (no drives running for certain). While downloading the program, the cabinet exploded. Fortunately, my electrician, who 2 minutes earlier was in the cabinet changing parameters, was standing back 10 feet as molten copper danced across the floor to his feet. We had a camera recording the area recording the entire event.

Root cause? The source was at the distribution block. I'm guessing we had a fray or maybe some grindings from conduit cut-in holes that crossed phase to phase. This cabinet had been in place for a few years, so it wasn't from any recent work.

My message to my electiricans - this was a completely random event. If it hadn't happened this day, it would have happened sometime while the line was running. The line would have stopped, the electrician called, and when he opened the door of the cabinet, he would have seen the back char and said "I see the problem". We've all had experiences like that and never really considered that it could have happened while we had our hands and faces in the cabinet.

No one did anything wrong that day. No amount of experience would have protected you that day. This is why we wear PPE rated for arcflash.

So to answer the original question: Go back to Robertmee's post about Arcflash and PPE.

 

[tim_callinan]

I appreciate all the replies. This really is a great forum. With the powerflex - Im looking at those remote controls - fecking nearly 600 bux for that! I put in a RFQ to rexel for a price on them. I think thats a good idea though- I appreciate it. I know you can remove the front cover to program it but my issue is these lads will be taking it off and on about 20 times a lab. They like to test a parameter and see how it runs. Id like to keep the front panel on TBH - they will end up destroying the drives if they remove them that much. Does anyone know if it is possible to provide the 525 with 24 v to set the parameters - we could then turn on the circuit breaker when we want to test the motor?

1) Right now - my plan is to put High voltage stickers on the cabinets.
2) Enforce the LOTO more stringently
3) Order electrical checkers and when the cabinet is opened- use the checker.
4) Im going to test out some gloves at rexel and see how dextrous they are.
5) Sort out the shafts sticking out.

About the arc flash - are arc flash PPE required for 208? Will normal safety glasses suffice. - If not, we'll buy the proper ones- I just want to double check.
Thanks again folks. I really appreciate it.
Tim

 

[robertmee]

For the HIM just buy used. 2 year warranty

https://www.radwell.com/Shop?source...yVumql3hl8x7okENgAIaJQQzoKKqhDCsaAru3EALw_wcB

Be sure it comes with the cable or buy one.

 

[robertmee]

Normal safety glasses are fine generally. Whether 208 is an arc flash danger or not depends. Some good discussion. https://brainfiller.com/arcflashforum/viewtopic.php?f=33&t=5416