1. Create Your User Profile and Status Updates

    Arc Flash Forum members are invited to create a user profile. Let others know who you are, what you do and even add a picture or avatar of yourself. What are you up to? Let people in the arc flash and electrical safety community know with "status updates"!
  2. Welcome to the All New Arc Flash Forum

    Arc Flash Forum is a community where we help each other learn about arc flash and electrical safety. There is still much to be learned about arc flash, standards, PPE, studies and more and We need your HELP!

    If you have good information about Arc Flash - Post It! If you have a question about Arc Flash - Post It! If you can provide answers to Arc Flash questions - Post it!

    Sign up as a today member! Feel free to link to this site www.arcflashforum.com. Tell your friends. We want to help everyone be safe in the workplace!
  3. Bigger and Better!

    As you have no doubt noticed, the forum has been through quite an upgraded and looks and feels very nice! There are loads of new features and ways in which this site can now be even more useful to the community in learning about Arc Flash and Electrical Safety.

    Create your detailed user profile
    Add a profile photo of yourself
    Like the forum on Facebook
    "Like" users' posts
    Publish your articles in the library
    ...and much, much more!

    Learn More About the New Features Here
Create Your User Profile and Status Updates Welcome Message Arc Flash Forum has been Upgraded!

Cf constant

Discussion in 'IEEE 1584 - IEEE Guide for Performing Arc-Flash Ha' started by Electric John, Mar 10, 2008.

  1. Electric John New Member

    Hi,

    For voltages above 1 kV, IEEE-1584-2002 proposes Cf = 1.5. I just read in the Electrical Safety and Arc Flash Handbook that engineers are changing this constant in the equation to Cf = 2.2 to better match laboratories results.

    Have any one changed this value with confidence?

    Thanks!
    Electric John, Mar 10, 2008
    #1

  2. WDeanN Well-Known Member

    John,
    I read Cf=1.5 for voltages below 1kV.
    I haven't heard of changing this value. Changing it up, especially to 2.2, would increase the energy levels significantly (by an additional 33%!). I would be interested in any justification for this as well.

    I try to avoid being overly conservative in my calculations, without some documented justification, because it reduces buy-in from the electricians, as well as management, to effectively implement an arc flash program.
    WDeanN, Mar 10, 2008
    #2

  3. Electric John New Member

    Hi WDeanN,

    you are correct, my mistake. Cf = 1.0 k for above 1 kV and Cf = 1.5 for below 1kV. Yes, increasing the Cf = 2.2 would increase the incident energy. It seems that IEEE-1584 std isn't enough conservative for voltages over 4.16 kV. Lee's method seems too conservative and IEEE-1584 not enough.

    I'm currently testing the Heat Flux calculations which seem to give better result for open air equipment at distribution voltage level.

    Thanks for you opinion.

    Electric John
    Electric John, Mar 10, 2008
    #3

  4. brainfiller Administrator

    Based on the IEEE test data, I think going beyond 1.5 would be quite an overkill. The Cf is based on establishing a "confidence factor" when comparing calculated PPE categories vs. PPE categories from test results.

    A comparison was made of the required PPE category based on tests, and then the PPE category was also calculated based on the (then) proposed IEEE incident energy equations. At lower voltages, the equations often gave PPE values that were lower than the test results gave. Multiplying by 1.5 adjusted the answers so that the equations gave a PPE class that was equal, and in a few cases, greater than the test data 95% of the time. They then called this a 95% confidence factor. If you increase the Cf higher than 1.5 you would likely end up with an even greater PPE level, beyond what a test might indicate.
    brainfiller, Oct 16, 2008
    #4

Share This Page