Is this safe? Controlling a live load using using the MCC

[3492f]

Hi All.
Great forum! I was trying to find an answer to an issue today and found your forum.
I work as a mechanic for a company that uses belt conveyors to move product.
When the conveyors were overwhelmed today with a lot of product, I saw building supervisors (who are neither mechanics or electricians) cycling off MCC bucket disconnects to control different sections of the belts.
It was to my understanding that this is unsafe. These buckets control 480v, 3 hp motors. I am in belief that the control stations should be utilized, followed by using the regular disconnects as a second choice, followed last by using the knife switch at the actual mcc.
I know that our motor controls centers haven't been tested/rated so they do not have any type of rating info instructing what level of ppe to wear. Supervisors here just wear street clothing.

I know why they do this. If they use the control station, it shuts down All of the belts. If they use a disconnect, they can cycle off sections and let product run out from a jammed area.
Nonetheless, it seemed like the most dangerous choice was made to do this at the bucket versus a disconnect.
From what I've read, it looks like an arc flash Can also take place at a disconnect but is it More likely to occur at a bucket?

To be clear, they are stopping and starting loaded belts abruptly by opening and closing disconnects manually, engaging and re-engaging the live load to the motor.

It's not my area of expertise so I definitely wanted to ask you all for some help.
If I'm wrong or over worried, no problem. If they are doing something that will surely lead to an injury, I'd like to come up with a plan to better help them going forward.

Thanks!

 

[EC Dan]

Using the lever on the bucket is basically turning the internal circuit breaker on or off. Using a circuit breaker as a normal means of switching a load on or off is not permitted by the NFPA. Having said that, if the condition of the bucket is well maintained and has all panels intact, then it's not likely to produce an arc flash from the switching action.

 

[ptonsparky]

Hi All.
Great forum! I was trying to find an answer to an issue today and found your forum.
I work as a mechanic for a company that uses belt conveyors to move product.
When the conveyors were overwhelmed today with a lot of product, I saw building supervisors (who are neither mechanics or electricians) cycling off MCC bucket disconnects to control different sections of the belts.
It was to my understanding that this is unsafe. These buckets control 480v, 3 hp motors. I am in belief that the control stations should be utilized, followed by using the regular disconnects as a second choice, followed last by using the knife switch at the actual mcc.
I know that our motor controls centers haven't been tested/rated so they do not have any type of rating info instructing what level of ppe to wear. Supervisors here just wear street clothing.

I know why they do this. If they use the control station, it shuts down All of the belts. If they use a disconnect, they can cycle off sections and let product run out from a jammed area.
Nonetheless, it seemed like the most dangerous choice was made to do this at the bucket versus a disconnect.
From what I've read, it looks like an arc flash Can also take place at a disconnect but is it More likely to occur at a bucket?

To be clear, they are stopping and starting loaded belts abruptly by opening and closing disconnects manually, engaging and re-engaging the live load to the motor.

It's not my area of expertise so I definitely wanted to ask you all for some help.
If I'm wrong or over worried, no problem. If they are doing something that will surely lead to an injury, I'd like to come up with a plan to better help them going forward.

Thanks!

Not an answer for your question.

Is this a new project that is still in development?

If not, someone seriously dropped the ball for the control design of this system. Cycling disconnects is a PP way to solve the problem.

The penny pinchers must have had the most influence.

 

[3492f]

Thanks all. Yeah... dropping the ball for the cheapest method wouldn't surprise me. The building is over 30 years old. I know the buckets are never cleaned out or maintained so there is a lot of dirt/dust in them.

 

[petersonra]

Sounds to me like you need to get a good controls engineer in there to take a look at the control scheme and tweak it so there's not so much manual intervention required. The fact that manual intervention is required on such a regular basis suggests that the control scheme needs to be rethought.

 

[ptonsparky]

Sounds to me like you need to get a good controls engineer in there to take a look at the control scheme and tweak it so there's not so much manual intervention required. The fact that manual intervention is required on such a regular basis suggests that the control scheme needs to be rethought.

Tweak might be an understatement.

 

[kwired]

No hand, off, auto switches in the controls?

Lots of places I been around is somewhat impractical to switch load at process type equipment from the MCC as it is usually remote from the process.

Using the lever on the bucket is basically turning the internal circuit breaker on or off. Using a circuit breaker as a normal means of switching a load on or off is not permitted by the NFPA. Having said that, if the condition of the bucket is well maintained and has all panels intact, then it's not likely to produce an arc flash from the switching action.

You have a reference for that?

 

[3492f]

From a safety standpoint, is there much difference in them using the actual bucket for this vs a disconnect?
The buckets are older and have three line fuses and overloads on the starters.

 

[EC Dan]

No hand, off, auto switches in the controls?

You have a reference for that?

My interpretation of 240.83(D) is that circuit breakers may only be used as switches for lighting if marked as SWD or HID, however I understand it might not be as clear cut as that. I will amend my comment to say using a circuit breaker as a routine means of switching (except in the case covered by 240.83(D)) is not recommended.

 

[3492f]

No hand, off, auto switches in the controls?

Lots of places I been around is somewhat impractical to switch load at process type equipment from the MCC as it is usually remote from the process.

You have a reference for that?

There are control stations at the beginning and end of the line.
They cycle off manually in the middle of the run to break box jams and still allow the packages to be carried away from a jammed area.
I think a modern facility would use flow sensors to stop belt sections automatically.

 

[ptonsparky]

A 3hp load is not much to switch at 480. Guessing that nothing was locked rotor.
I don't see where it was stated they are using breakers or fuses.

 

[kwired]

My interpretation of 240.83(D) is that circuit breakers may only be used as switches for lighting if marked as SWD or HID, however I understand it might not be as clear cut as that. I will amend my comment to say using a circuit breaker as a routine means of switching (except in the case covered by 240.83(D)) is not recommended.

Read it carefully, that section only for fluorescent and HID applications as well as only for 120 and 277 volt applications.

Then there is 404.1 that indicates that circuit breakers are also/can be "switches".

 

[petersonra]

Tweak might be an understatement.

You'd be surprised. A lot of times it does not take all that much to fix it, but sometimes it takes a fresh set of eyes and a different perspective to get it right.

 

[3492f]

A 3hp load is not much to switch at 480. Guessing that nothing was locked rotor.
I don't see where it was stated they are using breakers or fuses.

this is a pic of how most of the mcc buckets are setup.
Realizing that we don't have enough control stations, would you call it a dangerous practice to stop and start the equipment how they were doing it?
I'm trying to get clarity before bringing the issue to our "higher ups"

 

[EC Dan]

Read it carefully, that section only for fluorescent and HID applications as well as only for 120 and 277 volt applications.

Then there is 404.1 that indicates that circuit breakers are also/can be "switches".

The section pertains to a circuit breaker's markings when used as a switch, but I'll agree the wording is such that is it not exclusively limited to be used as a switch for the application described in that section.

 

[kwired]

View attachment 2560306 View attachment 2560306 this is a pic of how most of the mcc buckets are setup.
Realizing that we don't have enough control stations, would you call it a dangerous practice to stop and start the equipment how they were doing it?
I'm trying to get clarity before bringing the issue to our "higher ups"

Might not be wisest choice but don't see it really being code or safety issue either.

The contacts in the starter likely are more easily or less cost to replace when they have worn out than to replace that switch if it wears out from a lot of usage. For one thing replacing the switch likely means shutting the main bus down to do so, where just opening the disconnect should be sufficient to work on the starter.

 

[EC Dan]

There seems to be some control circuit wiring going to the door, is there a door mounted HOA switch?

 

[3492f]

There seems to be some control circuit wiring going to the door, is there a door mounted HOA switch?

That's for a trip indicator light

 

[kwired]

There seems to be some control circuit wiring going to the door, is there a door mounted HOA switch?

Could just be pilot light(s), but not impossible to be a HOA.

 

[petersonra]

View attachment 2560306 View attachment 2560306 this is a pic of how most of the mcc buckets are setup.
Realizing that we don't have enough control stations, would you call it a dangerous practice to stop and start the equipment how they were doing it?
I'm trying to get clarity before bringing the issue to our "higher ups"

I don't think it is dangerous so much as it may result in some minor reduction in equipment life the big problem imo is the time wasted in doing this kind of thing and what loss of production results.