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#149993 07/03/04 03:35 PM
Joined: Jul 2004
Posts: 11
J
Member
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.


Jim Humphrey
Arc Flash PPE Clothing, LOTO & Insulated Tools
#149994 07/12/04 07:10 AM
Joined: Mar 2002
Posts: 582
R
Ron Offline
Member
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).


Ron
#149995 07/12/04 12:43 PM
Joined: Apr 2004
Posts: 55
B
Member
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.

#149996 07/31/04 07:42 AM
Joined: Jul 2002
Posts: 8,407
Member
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?.

#149997 08/07/04 07:49 AM
Joined: Jul 2002
Posts: 8,407
Member
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!.

#149998 08/07/04 08:26 AM
Joined: Mar 2002
Posts: 582
R
Ron Offline
Member
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.


Ron
#149999 08/07/04 08:45 AM
Joined: Jul 2004
Posts: 11
J
Member
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.


Jim Humphrey
#150000 08/13/04 10:50 AM
Joined: Nov 2000
Posts: 2,148
R
Member
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.


Don(resqcapt19)
#150001 08/13/04 11:11 AM
Joined: Mar 2002
Posts: 582
R
Ron Offline
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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.


Ron
#150002 08/13/04 01:38 PM
Joined: Nov 2000
Posts: 2,148
R
Member
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


Don(resqcapt19)
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