Available Fault Current and PPE

[vecam001]

If a 480V electrical panel is to have thermal imaging performed, it would require the panel cover to be removed, however, the calculated available fault current value exceeds the maximum PPE protection. Since the PPE is not adequate for the calculated energy level, the panel cover cannot be removed. Are there any options available other than not to perform the task?

On a similar note, if the same panel was de-energized and locked out for the purposes of performing work on a circuit, the panel is considered energized until proven it is in a zero energy state, thereby, requiring PPE to be worn until verified. If the PPE is insufficient protection for the calculated available fault current value, what other options are available to verify a zero energy state and not compromise the safety of the employee?

MV

 

[richxtlc]

If the HRC is >4, then the next time the equipment is oos you can have the thermal imaging windows installed so that you can perform the thermal imaging with the panels closed. There is a least one manufacturer that has these windows.

As far as measuring for absence of potential on this cubicle, a voltage detector placed on a longer hot stick (provided the HRC level at that distance is reduced to the level of PPE that you have) may prove adequate for this measurement. A recalculation of the HRC at the new distance is required to determine this.

 

[jim dungar]

Incident energy calculations do not actually provide any information on what PPE is required for performing actual work. Many people will 'round up' a calculated incident energy value so that it corresponds to one of the HRC values that are part of the "task tables". This rounding up makes it fairly 'mindless', as well as providing a consistent method, to chose PPE.

NFPA70E suggests, through FPN's that refer to annexes, that PPE be chosen based on the risk associated with the energized work being performed as well as the available incident energy.

Incident energy drops off as the 'inverse of the square of the distance', so it is very easy to take an incident energy value at one distance and determine the new value based on a different distance. For example: an 80 cal/cm? value calculated at 18", using a voltage detector on a 36" hot-stick would result in an energy value of 20 cal/cm? instead.

 

[cornbread]

What is your up stream clearing device. We have lowered some of our relay settings in order to reduce the hazard.

 

[richxtlc]

The incident energy calculations do provide enough information so that a qualified individual would know what PPE is required for the job, or at least know where to get that information so as to wear the proper PPE. As far as the task lists in 70E are concerned, they make a lot of assumption concerning available fault current and clearing time. This assumes that the available short-circuit current is documented, the upstream protection has be calibrated properly, and the circuit breaker has be maintained as will perform i/a/w manufacturer's specifications. That's a lot of assumptions. Also, if you are conservative in your estimates, then you may be wearing PPE that is more combersome then required and therefore adds another degree of hazard. The higher the HRC the more difficult it is to perform any work. Knowing the correct calculated value offers you the ability to choose the proper PPE for the job. Too many people use these task lists improperly because they make the improper assumptions, they take the easy way out.

 

[zog]

Too many people use these task lists improperly because they make the improper assumptions, they take the easy way out.

Amen brother, I see that way too often.

 

[brian john]

If the HRC is >4, then the next time the equipment is oos you can have the thermal imaging windows installed so that you can perform the thermal imaging with the panels closed. There is a least one manufacturer that has these windows.

.

Window BARELY are sufficient for high voltage gear, due to the cost and number required to do an adequate job. Windows on 480 VAC level and lower equipment would be impractical, and basically worthless to perform a professional level thermal scan.

We install these on HV gear there is a VERY limited field of view.

 

[zog]

Window BARELY are sufficient for high voltage gear, due to the cost and number required to do an adequate job. Windows on 480 VAC level and lower equipment would be impractical, and basically worthless to perform a professional level thermal scan.

We install these on HV gear there is a VERY limited field of view.

And to add that many of the windows will not withsatnd the pressures from an arc flash. Some have been tested for that but many have not.