Production Operators and Disconnects

[GoldDigger]

It is difficult if not impossible to have certainty. You improve your odds by combining l-d-l with t-l-t where possible.
If you can have the equipment running when you open the disconnect you have a high level of confidence. Then follow up with l-d-l to confirm that you did not just interrupt the control circuit.
If you are working on the motor side of a starter, for example, then you can be relatively confident if you open the a combined starter disconnect, or if you find no voltage at the input to the starter.
It seems to me that the toughest problem is to verify that your action was in fact what removed power if there are multiple controls and disconnects that affect the same equipment.
What is your suggestion?

Tapatalk!

 

[don_resqcapt19]

It is difficult if not impossible to have certainty. You improve your odds by combining l-d-l with t-l-t where possible.

Most times l-d-l is not done for if the work that requires the lockout is mechanical, however that is required if the work is electrical in nature.

If you can have the equipment running when you open the disconnect you have a high level of confidence. Then follow up with l-d-l to confirm that you did not just interrupt the control circuit.

Unless the disconnect is local to the equipment there is still some question.

If you are working on the motor side of a starter, for example, then you can be relatively confident if you open the a combined starter disconnect, or if you find no voltage at the input to the starter.

True, however to work in a starter, you really have to open the disconnect that is upstream of the starter and that still leaves questions.

It seems to me that the toughest problem is to verify that your action was in fact what removed power if there are multiple controls and disconnects that affect the same equipment.
What is your suggestion?

Tapatalk!

The best solution to lockouts for mechanical work is a local disconnect that provides an "air break" that can be verified just by looking. A disconnect with a viewing window and a single conduit directly to the motor would work for me, as would Meltric type connection to the motor.

Electrical isolation for electrical work can also be that simple in some cases, but most often you have to have some confidence in the electrical drawings and the l-d-l testing.

When I was on a rescue squad, my plan for lockout, if we would ever need to do an industrial rescue involving motor driven equipment that did not have a local disconnect, was to use the jaws of life cutter on the power supply to the motor. I never had to do that, but I would have under those conditions.

 

[GoldDigger]

The jaws of life technique is very similar to the fire axe technique for solar PV panels.
Very definite, with no requirement for spending time locating remote devices or finding special tools.
The circumstances dictate the methods.

Tapatalk!

 

[cdevine]

Very interesting and most educational. Just so I understand the state of the art of verification for mechanical work...

The mechanical work verifier needs to determine two things:

1. has the correct device been isolated
2. has the energy been effectively isolated

While it seems the try-lock-try method addresses point 1, there is the remote possibility that it could give a misleading result and therefore may not address point 2 always. In addition, at times it can be inconvenient and then a live-dead-live check comes to the rescue. Sometimes even the live-dead-live check is challenging due to potential arc flash exposure and the availability of suitable PPE.

A visible blade or plug/socket solution satisfies point 1 and 2.

Mmmm. I suppose the advantages and disadvantages of the t-l-t (try start) method don't really surprise me. The experience of others I have spoken to doesn't give me a warm feeling about the use of the visible blade or plug/socket solution.

Just out of curiosity, if a try start (addresses point 1) was coupled with a means for non-electricians to perform a test similar to a live-dead-live check (addresses point 2) would that be valuable?

 

[don_resqcapt19]

The jaws of life technique is very similar to the fire axe technique for solar PV panels.
Very definite, with no requirement for spending time locating remote devices or finding special tools.
The circumstances dictate the methods.

Tapatalk!

Except with the solar, if it is day time, the solar conductors are more likely to be energized. With a motor that is not turning, it is much less likely that the motor conductors are energized.

My suggestion for the solar panels is to just use a 1500 - 2000 GPM stream from a straight tip on a tower ladder and blow the panels completely off the roof..

 

[don_resqcapt19]

...
Just out of curiosity, if a try start (addresses point 1) was coupled with a means for non-electricians to perform a test similar to a live-dead-live check (addresses point 2) would that be valuable?

There are places that use this product for mechanical work lockout out verification. It is my understanding that you can't use that product for electrical work lockout verification.

 

[cdevine]

There are places that use this product for mechanical work lockout out verification. It is my understanding that you can't use that product for electrical work lockout verification.

Thanks. It certainly does address the arc flash issue as you don't need to open the panel door.

However, for mechanical work, could you trust the test result as much as a live-dead-live test result given that it does not seem to allow you to perform the last "live" test?

 

[don_resqcapt19]

Thanks. It certainly does address the arc flash issue as you don't need to open the panel door.

However, for mechanical work, could you trust the test result as much as a live-dead-live test result given that it does not seem to allow you to perform the last "live" test?

Most places I have worked at don't require the l-d-l test for mechanical work...only for work on exposed possibly energized electrical equipment.


I did tell one company that if they wanted to be completely sure, just have the utility open the 34.5kV air break switches on the line side the transformer that services their plant

 

[cdevine]

Most places I have worked at don't require the l-d-l test for mechanical work...only for work on exposed possibly energized electrical equipment.

Which is similar to my experience but it seems to me that more companies are realising the short comings of try start, visible break and low tech, lamp indicator methods. The future of isolation for mechanical work appears to be a method that identifies that the correct equipment has been isolated as well as that the equipment has been effectively isolated. Aside from those basic needs, a set of second tier customer needs suggests current approaches just don't seem to cut it. To look at it another way the most frequent of isolations performed, LV isolations for mechanical work, is poorly serviced by current methods which are endorsed by legislation. Which reminds me of the quote by the famous comedian Oliver Hardy "Well, here's another nice mess you've gotten me into!" Now that I have had my rant, I feel much better now.

I did tell one company that if they wanted to be completely sure, just have the utility open the 34.5kV air break switches on the line side the transformer that services their plant

You've touched on a good point. To some extent HV isolators take verification much more seriously. HV isolations generally require that a set of working earths be placed as well. Placing earths on incorrectly verified isolations (energised) conductors tends to leave a mark in the verifier's mind .... and his underpants!