DISCONNECT BETWEEN MCC w/VFD AND MOTOR

[petersonra]

Then they have no need for lockouts ?????

That work would normally not be done by operators.

 

[TwoBlocked]

That work would normally not be done by operators.

In the plants you have been in, is there work that the operators do, that DOES require machinery being locked out?

 

[herding_cats]

Yaskawa dealer here:

You risk damaging the drive if you disconnect on the bus side (output) while the input power is active. NEVER disconnect the bus side at all.

We call this "cutting it's balls off" in the industry.

It's best to stop the drive before de-energizing it.

 

[petersonra]

In the plants you have been in, is there work that the operators do, that DOES require machinery being locked out?

Not normally. They do have procedures in place to make things safe when necessary but an actual operator locking out anything would be highly unusual

 

[kwired]

When is an operator typically allowed to do the type of maintenance that would require locking out a single motor?

How about when they are doing just about anything to the driven equipment and need to assure it can not start on them while working on it?

Of course they can always lock out back in the electrical room ahead of the drive instead of at a local disconnect, but guess which one will be utilized most cases if both exist?

 

[kwired]

I don't recall being in plants where operators perform these kind of tasks.

Ever been in food production plants where they need to disassemble machines or portions of them to clean them at times? Sometimes this can be daily or even between batches or when changing product/formulas.

Have a place that when they switch from products containing soy to non soy products they have to do a rather thorough cleaning of all equipment in the process. Can be other ingredients that trigger this as well but I know soy is one of them.

Clearing jammed/clogged equipment could be another reason depending on method needed to clear it, or replacing of cutters, screens, filters etc. that are routine production tasks.

 

[garbo]

I have seen this done for critical pumps that must run even if the VFD dies. An across the line starter is installed parallel to the VFD with addition contactors so full voltage is NEVER applied to the output of the VFD. Doing so can destroy the VFD.

Have to be carefull with some factory supplied drive bypasses. Most use three contactors. M1 to feed drive, M2 on output of drive and M3 is the bypass ( input of M3 are tied in with power input of M1 and the M3 output is tied into the output of M2 contactor ) . With the 3 contactor arrangement have seen the drive techs work on powered down drives while running the motor In bypass. Contrary to what a drive salesman told me all three contactors can never be energized at the same time. They have axillary contacts to prevent this. Some of these types have a test position on HAND-OFF- AUTO selector switch which I never saw anybody use. On some factory supplied bypasses they only use two contactors ( M1& M3 ). Our most commonly used brand of VFD'S that had 3 contactors the drive will not start until the M2 contactor is closed. We had over a hundred drives with bypass. During monthly ATS testing usually one old M2 contactor would not pull in all the way even while coil had 116 to 120 volts. This would produce a fault code.

 

[petersonra]

Ever been in food production plants where they need to disassemble machines or portions of them to clean them at times? Sometimes this can be daily or even between batches or when changing product/formulas.

Have a place that when they switch from products containing soy to non soy products they have to do a rather thorough cleaning of all equipment in the process. Can be other ingredients that trigger this as well but I know soy is one of them.

Clearing jammed/clogged equipment could be another reason depending on method needed to clear it, or replacing of cutters, screens, filters etc. that are routine production tasks.

I have been in a lot of food plants. I don't recall ever seeing operators performing these functions, but maybe I was not paying close attention.

It makes some sense now that you mention some of these tasks.

 

[Jraef]

Have to be carefull with some factory supplied drive bypasses. Most use three contactors. M1 to feed drive, M2 on output of drive and M3 is the bypass ( input of M3 are tied in with power input of M1 and the M3 output is tied into the output of M2 contactor ) . With the 3 contactor arrangement have seen the drive techs work on powered down drives while running the motor In bypass. Contrary to what a drive salesman told me all three contactors can never be energized at the same time. They have axillary contacts to prevent this. Some of these types have a test position on HAND-OFF- AUTO selector switch which I never saw anybody use. On some factory supplied bypasses they only use two contactors ( M1& M3 ). Our most commonly used brand of VFD'S that had 3 contactors the drive will not start until the M2 contactor is closed. We had over a hundred drives with bypass. During monthly ATS testing usually one old M2 contactor would not pull in all the way even while coil had 116 to 120 volts. This would produce a fault code.

This was the standard for years, but the heightened emphasis on Arc Flash safety has made this less common now. In that scenario, working on the VFD while in bypass would require being suited up with the appropriate PPE for the available fault energy, because the line side of the M1 and the load sides of M2 and M3 are all energized. That also then means having to get a “hot work permit” in a lot of places.

The Bypass can still be done, but I now recommend that the VFD be in its own package by itself with a separate line side disconnect, then the bypass can just be a stand alone combo interlocked 2-contactor starter in its own box next to it, with its own breaker. That way you don’t need the M1 contactor, because you isolate the VFD line side with its own disconnect. So back to the MCC concept then, this is all simpler in an MCC lineup, because that’s how everything would be arranged anyway. VFD in its own bucket, then just order a reversing starter as the bypass and modify the contactor wiring to not be reversing, then add some control interlock wiring between them and tie the VFD output to the input of one contactor in the other bucket. To work on the VFD, you put the motor in bypass, then open the disconnect for the VFD and pull the bucket out to work in it on the bench (and/or plug replacement VFD bucket in its place).

 

[Bwas]

As far as I can tell disconnects are required by 440.14.

For VFDs in MCCs, I don't like them. You basically have to de-energize the entire MCC to work on a single drive. If you can't turn off the MCC I'd use standalone VFDs.

 

[don_resqcapt19]

Not normally. They do have procedures in place to make things safe when necessary but an actual operator locking out anything would be highly unusual

The manufacturing plants I have worked in all had their operators do lockouts for code changes and clean out.

 

[kwired]

I have been in a lot of food plants. I don't recall ever seeing operators performing these functions, but maybe I was not paying close attention.

It makes some sense now that you mention some of these tasks.

Depending on how automated the plant is, you may have a majority of equipment that is CIP. depending on arrangements all they might need to do is manually connect CIP piping or hoses to certain items, others are always in place and flow is controlled by automatic valves. But even then there is likely a certain amount of items that do get some disassembly and have some components manually cleaned.

 

[kwired]

The manufacturing plants I have worked in all had their operators do lockouts for code changes and clean out.

Sometimes it isn't even clean out, you may need to disassemble or partially disassemble a machine to change screens, cutters, or other items that must change when you switch over to a different product/formula.

 

[milmat1]

I often have a local disconnect at the motor when the VFD/MCC is out of sight. But it provides feedback (aux contacts) to kill the VFD.
You do not want ever want to close the disconnect with a VFD already in run mode.