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Higher IE on CB Load Side
https://brainfiller.com/arcflashforum/viewtopic.php?f=4&t=884		 Page 1 of 1
Author:  viper57 [ Fri Jan 15, 2010 5:32 am ]
Post subject:  Higher IE on CB Load Side
Looking at an arc flash study done on a 13.8kV SWGR line up with main breaker. The detailed study shows a significantly higher IE (44.8 cal/cm2) on the load side of some of the breakers than on the SWGR bus (22.8 cal/cm2). These breakers are feeding large motors (5000+HP). Just doesn't seem right. :confused: What, if anything, might cause this?
Author:  Zog [ Fri Jan 15, 2010 6:48 am ]
Post subject: 
viper57 wrote:
Looking at an arc flash study done on a 13.8kV SWGR line up with main breaker. The detailed study shows a significantly higher IE (44.8 cal/cm2) on the load side of some of the breakers than on the SWGR bus (22.8 cal/cm2). These breakers are feeding large motors (5000+HP). Just doesn't seem right. :confused: What, if anything, might cause this?


Motor contribution is my guess, hard to tell without all the data. Possiblle you can adjust relay settings to lower this. Sounds like a good canidate for remote racking and switching.
Author:  viper57 [ Fri Jan 15, 2010 6:54 am ]
Post subject: 
How could motor contribution affect the load side and not the line side of the breaker? Could you send me a PM on your company and services offered? Thanks!
Author:  WDeanN [ Fri Jan 15, 2010 7:52 am ]
Post subject: 
It's also possible that there is some additional protection on the bus that does not protect the load side equipment, such as differential protection or zone selective interlocking. They may also be taking credit for maintenance settings on the relays at the bus, but not at the motors.

The numbers still seem high on the bus side for this, however. I would look at the study and see if they looked to upstream devices for miscoordination or faster operating times at the arcing fault current levels.
Author:  THE CABLE GUY [ Fri Jan 15, 2010 9:43 am ]
Post subject: 
Can you post a segment of your one-line that indicates what your speaking of? Sorry, I am a visual type of guy.
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