It is currently Thu Feb 22, 2018 3:44 am



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Motor Starter MCC
PostPosted: Wed Jun 03, 2009 5:11 am 
Offline

Joined: Tue Nov 11, 2008 1:49 pm
Posts: 3
I performed arc flash calculation using IEEE 1584 on a 480 volt three phase motor control center (MCC) and the incident energy level exceeds 1.2 cal/cm^2. Does the calculated value negate allowing an individual to perform a circuit breaker or starter operation with the enclosure door closed at a hazard risk category 0 based on Table 10.7(C)(9)?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Jun 03, 2009 6:38 pm 
Offline
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
Flame question?

MCCs are not switchgear and outside of the intent of high energy switching devices. With doors closed there are no exposed and energized components. Hence, NO PPE is required. If you want to use HRC0 thats higher than 'none' so go ahead.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Jun 04, 2009 7:04 am 
Offline

Joined: Tue Nov 11, 2008 1:49 pm
Posts: 3
Thanks for your reply.
Correction to my original post:
I'm referring to table 130.7(C)(9) under section (600v Class Motor Control Centers (MCC's) Note-2)

For example, we calculated incident energies on our 15kv switchgear and the energy levels are at Catagory-2. Per Table 130.7 (C)(9) (Metal Clad Swtichgear 1kv through 38kv) insertion or removal of circuit breakers from cubicles doors opened or closed is Catagory-4.

Is it acceptable for the task of insertion or removal of circuit breakers from cubicles doors opened or closed to wear catagory-2 PPE even though the table differs? If this is acceptable because of the calculated incident energy values, why would'nt the calculated energy values dictate the PPE clothing for 480v MCC's.

Do we follow the table or we follow our calculations?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Jun 04, 2009 8:34 am 
Offline
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
jjakubin wrote:
Thanks for your reply.
Correction to my original post:
I'm referring to table 130.7(C)(9) under section (600v Class Motor Control Centers (MCC's) Note-2)

For example, we calculated incident energies on our 15kv switchgear and the energy levels are at Catagory-2. Per Table 130.7 (C)(9) (Metal Clad Swtichgear 1kv through 38kv) insertion or removal of circuit breakers from cubicles doors opened or closed is Catagory-4.

Is it acceptable for the task of insertion or removal of circuit breakers from cubicles doors opened or closed to wear catagory-2 PPE even though the table differs?


Yes, the tables are based on many assumptions and tend to fail on the safe side (More PPE). If your calculated Ei is <8cal.cm2 you can use HRC 2 doors open or closed.

jjakubin wrote:

If this is acceptable because of the calculated incident energy values, why would'nt the calculated energy values dictate the PPE clothing for 480v MCC's.
It does, once you have done the study you should follow those PPE requirements.
jjakubin wrote:

Do we follow the table or we follow our calculations?


Calcs.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Jun 04, 2009 8:17 pm 
Offline
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
You have your choice of following either of two methods: under IEEE 1584 you calculate the IE at the point of interest and then use one PPE for all tasks; under NFPA Task Matrix you do NOT calculate IE at the point of interest and vary that PPE according to the table for a particular task. With the Table you need to verify Isc and OCPD (overcurrent protection device) clearing times are within the limits of the NOTES. You should not be co-mingling them together as that just creates the confusion you are experiencing now.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 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