Is it ever ok to work on exposed live parts per 70E?

[DanOmar]

Can someone explain what I am missing here? According to OSHA in order to work on live parts a qualified person must have appropriate PPE. When calculating the incident energy for an arc flash boundary the closer you get to the live parts the greater the incident energy. If one were to be in contact with live parts that distance would then be zero, in which case the incident energy would be infinite. Therefore there is no possible PPE you can use which would be adequate.

 

[Joe.B]

My understanding is the measurement is taken from the head/chest. So the distance shouldn't be zero, unless you're using your teeth to torque a lug...

 

[jim dungar]

The Incident Energy is typically based on a working distance of 18". As mentioned this is a typical distance finger tip to chest. Severe injuries to extremities are usually more survivable than those to a torso. NFPA 70E is willing to sacrifice your hands, are you?

 

[topgone]

Can someone explain what I am missing here? According to OSHA in order to work on live parts a qualified person must have appropriate PPE. When calculating the incident energy for an arc flash boundary the closer you get to the live parts the greater the incident energy. If one were to be in contact with live parts that distance would then be zero, in which case the incident energy would be infinite. Therefore there is no possible PPE you can use which would be adequate.

No electrical work is so important that you will have to work hot, IMHO. No amount of PPE can be worn when the energy level is above 40 cal/ cm2. If you are focused on the incident energy of the location that you are working on live, I hope your controller has a switch to select to maintenance mode so the incident energy is lessened due to quicker clearing time.
Be that as it may, I still believe shutting the system down is the safer option prior to servicing. Been burned, it ain't nice.

 

[Fred B]

No electrical work is so important that you will have to work hot, IMHO. No amount of PPE can be worn when the energy level is above 40 cal/ cm2. If you are focused on the incident energy of the location that you are working on live, I hope your controller has a switch to select to maintenance mode so the incident energy is lessened due to quicker clearing time.
Be that as it may, I still believe shutting the system down is the safer option prior to servicing. Been burned, it ain't nice.

Metering and testing are considered live work and some forms of testing generally cannot be done without being energized. Thus requirement of a "qualified person" in 70E, person should be able to evaluate overall condition of equipment to be worked on prior to having live contact of testing tools, determining min apparent risk of equipment catastrophic failure. (Electrician not a fortune teller though)

 

[jim dungar]

No amount of PPE can be worn when the energy level is above 40 cal/ cm2.

That is very old school teaching. The vast majority of high incident energy locations are due to extremely long exposure times due to there not being enough fault current to cause the protective devices to open quickly or someone not being able to move away from the arcing location.
For at least 6 years the PPE manufacturers have made equipment well in excess of 40 cal/cm^2.

One valid area of concern is the effects of the Arc Blast, how there is still no industry standard methodology for predicting a blast value.

 

[garbo]

That is very old school teaching. The vast majority of high incident energy locations are due to extremely long exposure times due to there not being enough fault current to cause the protective devices to open quickly or someone not being able to move away from the arcing location.
For at least 6 years the PPE manufacturers have made equipment well in excess of 40 cal/cm^2.

One valid area of concern is the effects of the Arc Blast, how there is still no industry standard methodology for predicting a blast value.

The large hospital / research center that I retired from had a building built 15 years ago that they purchased 50 cal/cm PPE for the dual service 13,200 switchgear. For the other four buildings we had 40cal PPE. Thank God they spent the extra money for built in battery operated cooling fan on the head hoods. They had junk GE 13,200 dual outdoor service at a new ambutory building that had a 124 cal arc flash label. Of course they installed a vent by operating panel at eye level guessing to incinerate you head during a big Arc fault blast. Typical GE switchgear that had problems with moisture where they had to install heaters inside of equipment to control humidity. Begged them to install forget what they call a remote operator station at least 20' from 13.2 breakers. We were told that above a 50 cal arc fault the blast will kill you no matter how high PPE worn.

 

[petersonra]

Can someone explain what I am missing here? According to OSHA in order to work on live parts a qualified person must have appropriate PPE. When calculating the incident energy for an arc flash boundary the closer you get to the live parts the greater the incident energy. If one were to be in contact with live parts that distance would then be zero, in which case the incident energy would be infinite. Therefore there is no possible PPE you can use which would be adequate.

I seem to recall the various calculations involved you having a 50% chance of third degree burns on your torso.

Bottom line is always going to be shut it down unless you can't do the work with the power off or you create a greater hazard by shutting off the power.

 

[JoeStillman]

All the arc flash stickers we make include the safe-working distance (18") and the glove class. It's never your bare hands or a short sleeve shirt.

 

[jim dungar]

We were told that above a 50 cal arc fault the blast will kill you no matter how high PPE worn.

I agree that is what many instructors, that were taught 20 years ago, have been teaching. But that is not mentioned at all in NFPA 70E. I believe it was taught partially because NFPA PPE categories only went to Cat 4. When NFPA 70 E changed from primarily using categories to using calculations many instructors and company safety policies, including the one I worked for, did not up date their language.

 

[hillbilly1]

No electrical work is so important that you will have to work hot, IMHO. No amount of PPE can be worn when the energy level is above 40 cal/ cm2. If you are focused on the incident energy of the location that you are working on live, I hope your controller has a switch to select to maintenance mode so the incident energy is lessened due to quicker clearing time.
Be that as it may, I still believe shutting the system down is the safer option prior to servicing. Been burned, it ain't nice.

I’ve seen gear lately that have that switch.

 

[hillbilly1]

The large hospital / research center that I retired from had a building built 15 years ago that they purchased 50 cal/cm PPE for the dual service 13,200 switchgear. For the other four buildings we had 40cal PPE. Thank God they spent the extra money for built in battery operated cooling fan on the head hoods. They had junk GE 13,200 dual outdoor service at a new ambutory building that had a 124 cal arc flash label. Of course they installed a vent by operating panel at eye level guessing to incinerate you head during a big Arc fault blast. Typical GE switchgear that had problems with moisture where they had to install heaters inside of equipment to control humidity. Begged them to install forget what they call a remote operator station at least 20' from 13.2 breakers. We were told that above a 50 cal arc fault the blast will kill you no matter how high PPE worn.

It’s the difference between an open casket and a closed casket!

 

[David Castor]

NFPA 70E allows for energized work under three specific conditions:

De-energizing would pose a greater hazard (e.g. hospital)
De-energizing is not feasible (testing, troubleshooting)
Less than 50 V.

If the work doesn't fall into one of these 3 categories, energized work is not permitted.

The "incident energy" is a calculated at a specific "working distance". This is an assumed distance from the likely source of the arc to the worker's chest or head, whichever is closer. At 600 V and below, it's generally assumed to be 18 inches. It's always been recognized that hands and arms could be exposed to higher incident energy if closer than the assumed working distance. IIRC, 70E says that additional protective measures may be required in some situations. As others have noted, the energized work procedures in 70E are intended to prevent serious injuries and fatalities.

 

[PaulMmn]

It’s the difference between an open casket and a closed casket!

"Oh, he looks so -tan-!"

 

[ggunn]

NFPA 70E allows for energized work under three specific conditions:

De-energizing would pose a greater hazard (e.g. hospital)
De-energizing is not feasible (testing, troubleshooting)
Less than 50 V.

If the work doesn't fall into one of these 3 categories, energized work is not permitted.

If you were to ask 1000 electricians if they have ever worked hot outside of those categories, how many do you think would answer "yes"? How many of those who answered "no" would have been telling the truth?

 

[Joe.B]

If you were to ask 1000 electricians if they have ever worked hot outside of those categories, how many do you think would answer "yes"? How many of those who answered "no" would have been telling the truth?

Depends on if you're talking about asking real electricians...

 

[don_resqcapt19]

NFPA 70E allows for energized work under three specific conditions:

De-energizing would pose a greater hazard (e.g. hospital)
De-energizing is not feasible (testing, troubleshooting)
Less than 50 V.

If the work doesn't fall into one of these 3 categories, energized work is not permitted.

The "incident energy" is a calculated at a specific "working distance". This is an assumed distance from the likely source of the arc to the worker's chest or head, whichever is closer. At 600 V and below, it's generally assumed to be 18 inches. It's always been recognized that hands and arms could be exposed to higher incident energy if closer than the assumed working distance. IIRC, 70E says that additional protective measures may be required in some situations. As others have noted, the energized work procedures in 70E are intended to prevent serious injuries and fatalities.

So an unplanned outage which could last for days or even weeks is a lesser hazard than scheduling an outage?

 

[topgone]

NFPA 70E allows for energized work under three specific conditions:

De-energizing would pose a greater hazard (e.g. hospital)
De-energizing is not feasible (testing, troubleshooting)
Less than 50 V.

If the work doesn't fall into one of these 3 categories, energized work is not permitted.

The "incident energy" is a calculated at a specific "working distance". This is an assumed distance from the likely source of the arc to the worker's chest or head, whichever is closer. At 600 V and below, it's generally assumed to be 18 inches. It's always been recognized that hands and arms could be exposed to higher incident energy if closer than the assumed working distance. IIRC, 70E says that additional protective measures may be required in some situations. As others have noted, the energized work procedures in 70E are intended to prevent serious injuries and fatalities.

Then you'll have to rack your brain into making justifications for the work on a live equipment.
Even if higher ups give their nod, it doesn't take the possibilities out that someone could get burned.
Even if the shutdown option is chosen, a break in the job communications can make an equipment already rendered "dead" go live, especially if the LOTO is easily defeated. It ain't comfy staying at the hospital for days for 3rd degree burns and nurses wake you up early morning for your daily debridement!

 

[hillbilly1]

Even with hospitals, it’s hard to justify, as they have backups for backups. They can’t depend on just one system. I did a temporary backup for the state of Florida payroll system. They already had a backup generator, but wanted a backup for it while they had the gear turned off to replace the computer room UPS. Another contractor was doing that, but I don’t think the engineer in charge of the project realized the UPS still had voltage in the bypass mode, but that wasn’t my problem!

 

[jim dungar]

It’s the difference between an open casket and a closed casket!

Again, a wrong old teaching based on scare tactics.