It is currently Thu Jan 27, 2022 11:21 pm

Author Message

 Post subject: arc flash calculations - worksheet b page 19 of free guidePosted: Wed Oct 17, 2012 2:20 am

Joined: Wed Oct 17, 2012 1:59 am
Posts: 7
Hi
I am struggling to understand where the figures in the above sample calculation step 1 are derived. I can see that 610/457.2 ^1.641 = 1.60506
but
12,670/8286^1.641= 2.009.
Can anyone help me understand where these figures are derived

thanks

Top

 Post subject: Posted: Wed Oct 17, 2012 3:04 am
 Plasma Level

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1637
Location: Scottsdale, Arizona
clive rayner wrote:
Hi
I am struggling to understand where the figures in the above sample calculation step 1 are derived. I can see that 610/457.2 ^1.641 = 1.60506
but
12,670/8286^1.641= 2.009.
Can anyone help me understand where these figures are derived

thanks

The information shown is for adjusting the incident energy from the normalized working distance of 24 inches (610 mm) to your distance of 18 inches (457) mm.

The adjustment is based on the ratio of the two distances raised to the exponent of 1.641 The theoretical exponent was traditionally “2” but IEEE testing shows that this value varies depending on equipment type. 1.641 is for a panel.

The basic concept is the incident energy decreases exponentially with increasing distance. It also increases exponentially as the distance decreases.

As far as the calculations, here is what I have:

(610/457.2)^1.641 = 1.605

Or as IEEE has it in their equations:

(610^1.641) / ( 457.2^1.641)

37215.7 / 23,186.5 = 1.605

The result of 1.605 means that the incident energy will increase by a factor of 1.605 when a person moves from the normalized distance of 24 inches to a working distance of 18 inches.

Hope this helps.

_________________
Jim Phillips, P.E.
Brainfiller.com

Top

 Post subject: Posted: Thu Oct 18, 2012 4:00 am

Joined: Wed Oct 17, 2012 1:59 am
Posts: 7
brainfiller wrote:
The information shown is for adjusting the incident energy from the normalized working distance of 24 inches (610 mm) to your distance of 18 inches (457) mm.

The adjustment is based on the ratio of the two distances raised to the exponent of 1.641 The theoretical exponent was traditionally “2” but IEEE testing shows that this value varies depending on equipment type. 1.641 is for a panel.

The basic concept is the incident energy decreases exponentially with increasing distance. It also increases exponentially as the distance decreases.

As far as the calculations, here is what I have:

(610/457.2)^1.641 = 1.605

Or as IEEE has it in their equations:

(610^1.641) / ( 457.2^1.641)

37215.7 / 23,186.5 = 1.605

The result of 1.605 means that the incident energy will increase by a factor of 1.605 when a person moves from the normalized distance of 24 inches to a working distance of 18 inches.

Hope this helps.

Hi Jim
Good to hear from you again, we met last week at Haydock Park in the U.K.

thanks

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 3 posts ]

 All times are UTC - 7 hours

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

 Jump to:  Select a forum ------------------ Forum Library / Articles The Lounge    Question of the Week - What Do You Think?    Arcflashforum.com Feedback and Announcements    Off Topic Discussions    News in Electrical Safety Arc Flash and Electrical Safety    General Discussion    Electrical Safety Practices    Equipment to Reduce Arc Flash Dangers    Personal Protective Equipment (PPE) Arc Flash Studies    General Discussion    Arc Flash Labels    Software for Arc Flash Studies    System Modeling and Calculations    NEW! Electrode Configuration Library – 2018 IEEE 1584 Codes and Standards    CSA Z462 Workplace Electrical Safety    EAWR Electricity at Work Regulations, HSE - Europe    OSHA CFR Title 29    IEEE 1584 - Arc-Flash Hazard Calculations    NFPA 70 - National Electrical Code - NEC (R)    NESC - ANSI C2 - National Electrical Safety Code    NFPA 70E - Electrical Safety in the Workplace    2015 NFPA 70E Share It Here    Arc Flash Photos    Your Stories    What's Wrong Here? by Joe Tedesco
© 2022 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883