It is currently Mon Aug 03, 2020 11:18 pm



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: arc flash calculations - worksheet b page 19 of free guide
PostPosted: Wed Oct 17, 2012 2:20 am 
User avatar

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
:confused:

thanks


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Oct 17, 2012 3:04 am 
Plasma Level
User avatar

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1498
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
:confused:

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
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Oct 18, 2012 4:00 am 
User avatar

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 for the reply.

thanks


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] 

All times are UTC - 7 hours


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

Jump to:  
cron
© 2019 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883