It is currently Sat Oct 21, 2017 7:06 am



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Arc Flash Data Collection above 40 calories/square centimeter
PostPosted: Mon Oct 28, 2013 7:21 am 
Offline
User avatar

Joined: Tue Jul 03, 2007 5:00 pm
Posts: 45
Location: Michigan
I still run into this from time to time and now I’m second guessing. If you are gathering data on a switchboard fed from the 480 volt secondary of a 1500 kVA utility owned transformer, what PPE do you wear?

There is a pretty good likelihood that the utility fuses would take a long time to operate which would result in an incident energy well above 40 cal/cm2. It is not possible to ask the utility to de-energize, all we want to do is open the enclosure and take a look. What is everyone doing with this? Thanks!


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Oct 28, 2013 7:53 am 
Offline
Arc Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 676
Location: Rutland, VT
What I usually try to do is to get all the utility information prior to gathering any information on site. From the utility I request the txf protective device, riser cable info, txf info. I will then make a reasonable, based on NEC, assumption on secondary conductors and usually have an idea of length. This gives a reasonable approximation of what the afh is at the switchboard/switchgear. I also look at the 2 second cutoff if it is appropriate to use.
If it is still Extreme Danger, this is where the risk assessment of the hazard of the work you are trying to accomplish could come into use. Or you can make some assumptions on the bkrs based on the switchboard. In some cases, I have waited until there was a complete shutdown, including utility opening the fuses.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Oct 29, 2013 11:10 am 
Offline
Sparks Level

Joined: Fri Apr 15, 2011 7:43 am
Posts: 151
Location: Colorado
JoeB, you are correct that most utility fed panels are a high AFHC. When I collect data for the utility feed I am the most nervous due to the probable rating. In nearly all cases, to get the utility to shut off the power is very difficult and sometimes costly.
To determine the PPE to wear for the utility connection is no different than any other place in the system. You can actually find places in the system that are worse than the utility connection.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Nov 12, 2013 8:54 am 
Offline
Sparks Level

Joined: Sat Nov 21, 2009 10:23 pm
Posts: 72
Location: Ohio
It is virtually impossible to find a higher incident energy than on the customer side of the service point, which is usually the 480V service equipment when supplied by a utility owned transformer. Keep in mind the incident energy at the service equipment is not reduced by a main service disconnect unless the equipment is true compartmentalized switchgear. This is one slide is from a presentation I did for an IAEI State Chapter meeting. It is very conservative and has some very good support data.

Due to liability concerns, I indicated "work-de-energized" above 40 cal/sq. DOES THE DATA BELOW SURPRISE ANYONE?


[ATTACH=full]335[/ATTACH]


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 4 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 1 guest


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:  
© 2017 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883