Twistlock and VFD

[ptonsparky]

I have a customer that wants to use a twist lock to disconnect his motors from a VFD. Load side.

I only see problems but I don't have any experience to say otherwise. The VFDs would be off when the disconnect...we hope. Thoughts.

 

[iceworm]

I haven't seen this done as an industry practice - but I also don't think that matters.

I'm guessing "Twist-lock" implies flexible cord, per 400.7.A.6 or 400.&.A.8. If so, 400.7.B requires an attachment plug. Looks okay to me.

Yes, definitely be good if the equipment is locked out when the attachment plug is disconnected. Would that be handled through normal LOTO procedures? Probably.

ice

 

[petersonra]

I do not see an issue with it.

I see no reason why one would need to LO the VFD before opening the plug. Probably a good idea to stop the motor by whatever process you normally use to do so. But even if you did not do so, with modern VFDs it probably would not harm them any. They might trip though as some of them will trip if they detect no or unbalanced load while running.

 

[Besoeker]

I have a customer that wants to use a twist lock to disconnect his motors from a VFD. Load side.

I only see problems but I don't have any experience to say otherwise. The VFDs would be off when the disconnect...we hope. Thoughts.

I assume by twist lock, you mean a plug and socket arrangement?
Unplugging a dead VSD is fine. My concern is how you ensure the VSD is off, powered down when you did so. A locked connector with a key release system on the drive maybe?
And early break pin in the connector?

 

[Besoeker]

I do not see an issue with it.

I see no reason why one would need to LO the VFD before opening the plug. Probably a good idea to stop the motor by whatever process you normally use to do so. But even if you did not do so, with modern VFDs it probably would not harm them any. They might trip though as some of them will trip if they detect no or unbalanced load while running.

It might not harm the VSD. But nowhere I've been would allow you to unplug a live running motor. And I certainly wouldn't do it.It's an avoidable risk. We should avoid avoidable risks.

 

[petersonra]

It might not harm the VSD. But nowhere I've been would allow you to unplug a live running motor. And I certainly wouldn't do it.It's an avoidable risk. We should avoid avoidable risks.

I don't disagree that it is a good idea to stop the motor before unplugging it, and I said so. I don't see that it is necessary to lock it out first though.

 

[Besoeker]

I don't disagree that it is a good idea to stop the motor before unplugging it, and I said so. I don't see that it is necessary to lock it out first though.

What's to prevent someone from starting the drive while you are unplugging it?

 

[petersonra]

What's to prevent someone from starting the drive while you are unplugging it?

nothing, but it would probably not create a hazard so why would it matter?

 

[ptonsparky]

No problems seen with the device connection itself? They will handle the higher frequencies involved or at least no worse than normal. 5hp 480v.

 

[Besoeker]

nothing, but it would probably not create a hazard so why would it matter?

Probably not?

That simply isn't good enough. You wouldn't get that by a safety inspector or a risk assessment.
Particularly if the means to lock off the supply was available.

 

[petersonra]

Probably not?

That simply isn't good enough. You wouldn't get that by a safety inspector or a risk assessment.
Particularly if the means to lock off the supply was available.

If there is an identifiable hazard, then lock it out first.

If not, why bother?

if you want to have a blanket policy of locking out such motors before unplugging them in your facility, you are entitled to do so.

 

[Besoeker]

If there is an identifiable hazard, then lock it out first.

Working on live equipment is deprecated. And, if you don't isolate the drive, the connections in the plug/socket are live even without the motor running unless there is a physical disconnect between drive and motor.
Apart from that, there is the hazard of the drive being started, remotely in many cases, before you make that disconnection.. Is the plug/socket rated to break that current? What happens if it isn't?
I've seen first hand what can happen. And it isn't pretty.

The "probably not" isn't acceptable particularly if you can take simple steps to get a "definitely not".

 

[GoldDigger]

I would turn the motor off before unplugging, even though the connectors may well have a load break horsepower rating on them.
And if there is a disconnect in plain sight, I probably would not worry about LOTO at the disconnect, I would just eyeball it before plugging or unplugging.

Sent from my XT1080 using Tapatalk

 

[don_resqcapt19]

You can use an expensive plug an receptacle and meet all of the safety standards and you can even get a first break connection for a VFD shut down in the plug and receptacle. Take a look at the Meltric products. If you are not allowed to use a cord in your location you can connect flexible conduit to the Meltric plug.

 

[Besoeker]

You can use an expensive plug an receptacle and meet all of the safety standards and you can even get a first break connection for a VFD shut down in the plug and receptacle.

Or you can lock off the supply to the VSD.

 

[ptonsparky]

My gripe. They have 3R non fused disconnects with a control pole. Used but entirely suitable for the needs. They want twist locks. They also want lowest installed price. These motor will not move for the life of the equipment, which is another consideration.

 

[iceworm]

My gripe. They have 3R non fused disconnects with a control pole. Used but entirely suitable for the needs. They want twist locks. They also want lowest installed price. These motor will not move for the life of the equipment, which is another consideration.

So, they are not doing this for per 400.7.A.6 or 400.7.A.8? Then:

How come flexible cord is okay?
Why bother with the disconnect?

I'm lost.

ice

 

[ptonsparky]

So, they are not doing this for per 400.7.A.6 or 400.7.A.8? Then:

How come flexible cord is okay?
Why bother with the disconnect?

I'm lost.

ice

That is what they want to do. Flexible cord. I do not. In hindsight, I should have quoted the article instead of telling them it was a bad idea.

I feel 430.102 (B)(1) is what needs to be satisfied. The controller disconnect (2) is out of sight. Exceptions (a) and (b) do not apply.

 

[don_resqcapt19]

Or you can lock off the supply to the VSD.

A lot of places specify the disconnect to be at the motor.

 

[don_resqcapt19]

That is what they want to do. Flexible cord. I do not. In hindsight, I should have quoted the article instead of telling them it was a bad idea.

I feel 430.102 (B)(1) is what needs to be satisfied. The controller disconnect (2) is out of sight. Exceptions (a) and (b) do not apply.

The informational note to (a) suggests that the very fact that the motor is on a VFD is reason enough to eliminate the disconnect at the motor.