ECN Forum
Posted By: jhumphrey Energized Work NFPA 70E - 07/03/04 07:35 PM
Is anyone following or have information on the "new" section in the NFPA 70E on safe work practices when working energized?

As I read it... It's gives options but will require arc fault calculations, hazard approach calculations etc,, to determine PPE requirements.

This is going to require some changes in my safety manual and/or safe work practices.
Posted By: Ron Re: Energized Work NFPA 70E - 07/12/04 11:10 AM
I think you can get the approach distances and PPE requirements from NFPA70E directly. There is a table that has recommended PPE if you don't want to do the calculations, but your application must fit within the notes at the bottom of that table (fault available and clearing times).
Posted By: Big Ed Re: Energized Work NFPA 70E - 07/12/04 04:43 PM
The NFPA 70E will give you those values, but they are sometimes overly restricive. I work at a small power generator. One of the plants that our company owns went ahead and did the calculations (actually brought in a contractor) and significantly lowered some of these values.
We are preparing to bring in someone to do the calculations as well. When you really get into the text, start figuring "flash in a box" and other modifiers to the standard values, you find that you need the "moon suit" an awfull lot of the time.
Posted By: Trumpy Re: Energized Work NFPA 70E - 07/31/04 11:42 AM
Ron,
Are the NFPA 70E values a sliding scale?
How does this table work?
Live work is nothing to be sneezed at, in the least, having quite a bit of experience in it myself at the higher voltages.
I have, never worn a "Moon-Suit" though at any voltage, even when jointing Live 66kV lines.
I'm assuming that 70E encompasses work under 600V?.
Posted By: Trumpy Re: Energized Work NFPA 70E - 08/07/04 11:49 AM
Ron,
Other side of the coin,
If we started turning up to work in places in a "Moon Suit".
Maybe then people would understand just how dangerous this stuff is!.
Posted By: Ron Re: Energized Work NFPA 70E - 08/07/04 12:26 PM
Turmpy,
NFPA 70E has a table that lists the type of equipment, and the activity you plan to perform. Then it lists the PPE required. Unfortunately, most folks ignore the notes that apply to the table, which require a particular maximum clearing time. Sometimes that doesn't happen.
Posted By: jhumphrey Re: Energized Work NFPA 70E - 08/07/04 12:45 PM
Ron... people probably won't read the "fpn" and as a result may expose them themseleves to greater hazards or incorrectly assume they are protected but how many "electricians" do you think can and/or will be able to perform and understand the actual/alternative calculations.

Looks like we're headed into another area to protect people with a standard/regulation instead of requiring them to use safe work practices to begin with.
Posted By: resqcapt19 Re: Energized Work NFPA 70E - 08/13/04 02:50 PM
As we study 70E and work on providing the correct PPE, the one thing that I don't like is the permitted reduction in PPE level based on the clearing time of a breaker. I just don't think that any reduction that depends on the proper operation of an electrical mechanical device should be permitted.
Posted By: Ron Re: Energized Work NFPA 70E - 08/13/04 03:11 PM
The more I review and perform arc flash calculations, I realize that the table provided in 70E for PPE levels, is inappropriate to keep in the standard. In many situations, I find the notes (not even fpn) do not apply to the situation due to slower than noted clearing times.
In order to use the table, and to verify whether the table notes apply, you have to calculate a bolted fault current, then the associated arc fault current, then find a copy of the OCPD characteristics to see how long it takes for the device to clear. In many cases, I find that the arc fault current only activates the OCPD in the short or long time region which eliminates the possibility of using the table.
The table seems to be there for folks not able to perform the calcs, but you need to do some preliminary calcs to see if the table and the associated notes apply at all. Doesn't make logical sence to me to have the table, as it will give a false sence of security to someone when the ignore the notes.
Posted By: resqcapt19 Re: Energized Work NFPA 70E - 08/13/04 05:38 PM
Ron,
Quote
as it will give a false sence of security
It is my opinion that using the trip or clearing times for a breaker also provides a flase sense of security. What if the breaker settings have been changed? What if the breaker doesn't work? If it is a large system with protective relays, what if the batteries that provide the trip current are dead? I think that the PPE should be based on the arc flash that would occur if the OCPD does not operate.
Don
Posted By: Ron Re: Energized Work NFPA 70E - 08/13/04 06:58 PM
Don,
The result of the calculation, if you considered that the breakers didn't open, would surely be much higher than the highest rated PPE (following 70E, 40 cal/cm^2). You wouldn't be able to do any energized work, such as taking IR scans.
In many locations that I calculate using IEEE 1584 formula, and considering that the breakers or fuses operate, I get values in excess of achievable PPE.
Posted By: DougW Re: Energized Work NFPA 70E - 08/14/04 02:18 AM
An FD to the south of us had a LODD (Line Of Duty Death) of a Deputy Chief investigating an alarm at a shopping mall. Turns out the mall went into alarm because of a "brownout" D/T a dropped phase... unknown cause. After returning the engines, the Chief went into the panel room with the site electrician and an "engineer" for the property. They were discussing the situation when a) either the faulted UG line re-energized after OCP reset or b) the contractor digging 1 1/2 miles away struck the other phase and caused the short to fault at the point of least resistance - the panel for the mall. The arc flash and molten metal nailed him and the engineer.

IIRC, 2 & 3rd degree burns over something like 80-90% of his body surface. He was concious after the incident, and directed the crews responding to take care of the other victim before him. They knocked him out at the hospital - he lived for about a week after the incident. He wasn't wearing turnouts (Nomex FR) because he'd determined that there wasn't a fire on location, and was only 'investigating'.

Admittedly, a rare situation, but I noticed a lot less joking about my "other" job at the FD after the incident...
Posted By: KennyFrank Re: Energized Work NFPA 70E - 08/14/04 03:56 AM
oh my. I think I remember this... at a mall that is near county borders not far from a tollway. Incedents like this always give me a bit of a wake up call, in that I find myself stopping and reviewing and thinking more about the 'unforseen' but 'still remotely possible' things that could happen while in similar situations - somewhat of a reminder to guard myself against getting complacent about safety and safe working methods.
Posted By: GamecockEE Re: Energized Work NFPA 70E - 08/19/04 02:16 PM
I know of a couple of instances around these parts where arc flash has took it's toll as well. I don't think that the majority of EC's & even large corporations are paying attention to this. They are still thinking shock protection.

Having done arc flash assessments for a large industrial facility, the upper management did allow us at that time to make some changes to easily done things such as relay settings, but balked when it came time to pony up to such things as mandating Nomex clothing and changing long-time practices. The problem is that protective device setting is a lot of times it's a compromise to begin with, particularly with the setting of relays, and focuses on protecting equipment and maintaining electrical continuity, not protecting more fragile human beings.

Having been able to listen to Lanny Floyd in person once and doing some reading on the issue, basically in the worse case, one strives to make the event at least surviveable, not necessarily walk away with no injury whatsoever. The values that it takes to hurt a person is very small compared to the energy capable of being produced if a fault is allowed to linger.
The path to progress is paved in blood unfortunately.
Posted By: resqcapt19 Re: Energized Work NFPA 70E - 08/19/04 02:39 PM
I continue to have a fundamental problem with accepting the use of breaker settings and trip times to reduce the level of PPE that is required.
Don
Posted By: GamecockEE Re: Energized Work NFPA 70E - 08/19/04 03:27 PM
resqcapt19,
I don't think that is realistic, as you are aware time to the point that the arc is extinguished plays a role in the energy equation. I agree that all the things you talked about can happen, but it's better to have protection based on what will most likely occur and more defensible from an economic standpoint. We all know hot work is going to be done, at the very least particularly of the testing nature (how else can you verify the de-energized state)
Posted By: Trumpy Re: Energized Work NFPA 70E - 08/21/04 08:23 PM
Don,
I must say that I agree with you, I don't really like the idea of reducing your level of PPE, based upon a certain Circuit Breaker rating, anymore than what you do.
To my way of thinking, a CB has an Inverse Time-Current characteristic under fault conditions and therefore, even if it does trip near instantly, it's going to be carrying a fair amount of current.
Elderly CB's have a habit of failing catastrophically, especially where a Dead Short has occured down-stream. [Linked Image]
© ECN Electrical Forums