arc flash "Dangerous" levels...

[zog]

The way I understand the code is that if an enclosure is rated as "arc flash dangerous", that means you are not allowed to work inside the space while energized. You're good to go if you de-energize the enclosure.

How do you prove it is de-energized?

 

[adamscb]

How do you prove it is de-energized?

Fluke sells these amazing devices called voltmeters

Also, make sure that the breaker is in the 'off' position.

 

[wbdvt]

Fluke sells these amazing devices called voltmeters

Also, make sure that the breaker is in the 'off' position.

Well, I believe what Zog was referring to is that you cannot consider it de-energized without testing. So consider the case of a piece of equipment that needs to be verified as de-energized prior to working on it and it is 480V and has an incident energy level of 55 cal/cm2 at a working distance of 18" which would be about the distance from where the probes are placed to your chest. It must be considered energized until the DVM tells you otherwise so what arc rated PPE do you wear to do this testing?

 

[zog]

Well, I believe what Zog was referring to is that you cannot consider it de-energized without testing. So consider the case of a piece of equipment that needs to be verified as de-energized prior to working on it and it is 480V and has an incident energy level of 55 cal/cm2 at a working distance of 18" which would be about the distance from where the probes are placed to your chest. It must be considered energized until the DVM tells you otherwise so what arc rated PPE do you wear to do this testing?

Exactly my point

 

[big john]

...An incident energy level of 55 cal/cm2 at a working distance of 18" which would be about the distance from where the probes are placed to your chest. It must be considered energized until the DVM tells you otherwise so what arc rated PPE do you wear to do this testing?

Hot stick mounted voltmeter to keep you outside the AFB.

I'd much rather be at the end of a stick with minimal PPE than climbing into a cubicle wearing a bomb suit, even if it was rated for the task.

 

[topgone]

Hot stick mounted voltmeter to keep you outside the AFB.

I'd much rather be at the end of a stick with minimal PPE than climbing into a cubicle wearing a bomb suit, even if it was rated for the task.

To add another simple question re "de-energized" concern, what if the cubicle you're in gets suddenly "energized" (after verifying it was "de-energized")?

 

[GoldDigger]

To add another simple question re "de-energized" concern, what if the cubicle you're in gets suddenly "energized" (after verifying it was "de-energized")?

That is the purpose of Lock Out / Tag Out. And in some cases visible break disconnecting means.
Among other things it is a very good reason why locking out the control circuit of a contactor or controller instead of the actual power leads is not allowed.

 

[MD84]

That is the purpose of Lock Out / Tag Out. And in some cases visible break disconnecting means.
Among other things it is a very good reason why locking out the control circuit of a contactor or controller instead of the actual power leads is not allowed.

Agreed. >600V requires suitable protective grounds installed as well. In cases where fault current exceeds 50kA the grounds will likely fail and in this case a double isolation would be recommended.

I also would not recommend sticking your DVM in that location classified as dangerous. A visible open with a three point "hot/cold/hot" check using a non-contact voltage tester would be preferable.

Always hot/cold/hot check. This would mean that you select a voltage detector capable of safely measuring the nominal system voltage. Test for presence of voltage. De-energize equipment and perform lock out tag out. Using the same voltage detector and without manipulating the device check for loss of voltage. Using the same voltage detector and without manipulating the device check for voltage on a known live source of the same nominal voltage. Ground system if required. These steps should be performed using properly tested and calibrated equipment and using proper PPE and safe work practices as defined by the company work procedures, arc flash hazard analysis, and job hazard analysis.

Sometimes you may come across a situation where the equipment has tripped and you need to verify it is dead. In this case you can perform a hot check on another piece of equipment, cold check the the tripped equipment and then hot check the other energized equipment. Sometimes there is no other energized equipment to use as a verification your voltage detector is working properly. In this case a signal generator can be used, a car alternator or otherwise.

 

[MD84]

Fluke sells these amazing devices called voltmeters

Also, make sure that the breaker is in the 'off' position.

What if the circuit breaker shows off but the contacts are actually welded closed?

Checking with a non-contact voltage detector and establishing an electrically safe work condition would be recommended. I do not think that opening doors and checking for voltage is considered work and can be done using proper PPE and safe work practices.