It is currently Mon Mar 08, 2021 6:57 pm



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Question on info on a label
PostPosted: Thu Dec 02, 2010 9:20 pm 
Sparks Level

Joined: Mon Mar 29, 2010 5:02 am
Posts: 136
I was out installing labels today on some sites and am now looking for some help with how to interpret the label.. Mainly a "How would you read it"...

The Labels are:
- for a 480 volt MCC
- the Arc Flash Rating for the Line and Load side of the Breaker are the same (48.0 cal/cm2) and as such there is "no PPE available".

Now my question... I have the LINE side values clear as mud, but does the LOAD side include the Load Side of the Main Breaker, the bus, and the Line Side of the disconnects in the starters? Or does it include the Load Side of the Main Breaker, the bus, the Line Side of the disconnects in the starters, the starter, and all connections up to the LOAD wires (Motor Feeder, Transformer Feeder, etc)? Or is it only the Load side of the Main breaker and the bus?

NOTE: Not looking to breakdown the Arc Flash study, but just how to read the label.

We may be looking into revisiting some of the sites in the study, and possibly adding Arc Reducing Controls.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Dec 03, 2010 7:12 am 
Sparks Level

Joined: Wed May 13, 2009 3:19 pm
Posts: 56
Low voltage MCCs have been a continuing problem for us, specifically when they return high incident energy values. We’ve been treating the MCC Bus, the individual starter buckets, and all the parts within (MCP, Starter, Overloads, etc) all at the value calculated for the MCC Bus. We’ve debated the typical molded case breaker within the bucket should be very fast resulting in a very low hazard level for load side faults (i.e. working within the bucket). However, we see the problem being the protective device (the molded case breaker) is within the working location, in other words, the breaker which could quickly clear the fault is within the same location you are working. Another concern is there's typically no means to restrict access to the “line side” of the breaker. We’ve seen some examples of individuals attempting to remove a breaker from a starter bucket, while the bucket is still engaged to the MCC bus, resulting in a very bad outcome.

Therefore we assume the next device upstream as the primary clearing device for activities within the starter bucket. This is either the MCC main or the supply transformer high side over current protection if the MCC does not have a main breaker (most of ours do not). We typically look at engineering solutions to lower the incident energy potential to within Level 2 PPE for the entire MCC whenever possible. For working locations supplied from the MCC we do take credit for the protection within the starter bucket.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Dec 03, 2010 7:54 am 
Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 525
Location: Wisconsin
SCGEng1 wrote:
Therefore we assume the next device upstream as the primary clearing device for activities within the starter bucket. This is either the MCC main or the supply transformer high side over current protection if the MCC does not have a main breaker (most of ours do not).

This is what we do also.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Dec 03, 2010 8:46 am 
Sparks Level
User avatar

Joined: Tue Oct 26, 2010 5:00 pm
Posts: 195
Location: Maple Valley, WA.
[quote="glen1971"]
....LOAD side include the Load Side of the Main Breaker, the bus, and the Line Side of the disconnects in the starters? Or does it include the Load Side of the Main Breaker, the bus, the Line Side of the disconnects in the starters, the starter, and all connections up to the LOAD wires (Motor Feeder, Transformer Feeder, etc)? Or is it only the Load side of the Main breaker and the bus?....
QUOTE]

The AF values for the load and line side device could be the same because both the MCC main and upstream (from the MCC) breakers are the same mfg/type and have identical settings. Another reason could be the upstream protective device will trip before the main breaker (called mis coordination option in SKM.) This option will cause SKM to use the upstream device to determine the energy values instead of the slower Main breaker. This is why we put the protective device that was used to determine the energy level our labels.


You do not have the required permissions to view the files attached to this post.

_________________
Robert Fuhr, P.E.; P.Eng.
PowerStudies


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sat Dec 04, 2010 9:30 am 
Sparks Level

Joined: Mon Mar 29, 2010 5:02 am
Posts: 136
Thanx for the posts... With the rating on the LOAD side of the Bus I assumed that it carried through to the LINE side of the breaker. SCGEng1 made a good point and I think that will probably lead to a revist on the Arc Flash Study and possibly the installation of Arc Reducing Devices.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Dec 06, 2010 9:20 pm 
Sparks Level

Joined: Mon Mar 29, 2010 5:02 am
Posts: 136
glen1971 wrote:
Thanx for the posts... With the rating on the LOAD side of the Bus I assumed that it carried through to the LINE side of the breaker. SCGEng1 made a good point and I think that will probably lead to a revist on the Arc Flash Study and possibly the installation of Arc Reducing Devices.


After consulting the client they are going to be revisiting the study and confirming the numbers.. Then looking at how to reduce the Incident Energy to one where it can be worked on.

The conclusion they came to was that the LOAD side of the Main Breaker fault calculations carry through each starter to the T1/T2/T3 terminals, as the starter breaker won't clear a fault quick enough to lower the energy levels..


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 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