It is currently Tue Dec 12, 2017 2:59 pm



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Switchgear Main CB used as Clearing Device
PostPosted: Thu Dec 18, 2014 12:39 pm 
Offline

Joined: Thu Dec 18, 2014 12:23 pm
Posts: 1
In a Low Voltage Unit substation configuration, with Eaton, Magnum draw out CB's with ARM's Switches.

Can the Main CB be used as a clearing device for the switchgear bus? The main is integral to the switchgear. Is this acceptable to IEEE1584?

Eaton states the that the Main CB can be used as a clearing device for the switchgear bus. However, I believe that IEEE 1584 states that the Main CB (clearing device) needs to be upstream and in a separate enclosure.

Please provide clarification.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Switchgear Main CB used as Clearing Device
PostPosted: Thu Dec 18, 2014 9:41 pm 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1820
Location: North Carolina
It depends on how "separate" it is. In a panelboard, clearly it is not separate. Same is true in an MCC vertical section. In switchgear though there is not much of an opening from section to section. In an MCC horizontal bus some are more isolated than others so its a judgement call, also dependent on how likely an arc flash in the horizontal bus is (usually not). So these generalizations result in usually switchgear being considered isolated except some metal enclosed gear, MCC's only in horizontal direction, and never in a panelboard.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Switchgear Main CB used as Clearing Device
PostPosted: Mon Dec 22, 2014 8:22 am 
Offline
User avatar

Joined: Wed May 23, 2012 11:59 am
Posts: 19
Location: Massachusetts
I had similar dilemma in the past and after talking to Cutler Hammer, Schneider Electric and GE I determined that Main CB in a Switchgear cannot be assume d as clearing device. All manufacturers states that most of their gear is open between sections and even when the opening for busing or wiring was small the separation wall has not been tested for arc flash events.

I do understand what PaulEng is saying, but I can't seem take on the liability based on my assumptions when not backed by some industry standard or manufacturer's email.

If you however have the email from them stating it will serve as clearing device, maybe you could use it after all.

Marek


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Switchgear Main CB used as Clearing Device
PostPosted: Mon Dec 22, 2014 12:53 pm 
Offline

Joined: Tue Sep 17, 2013 7:35 am
Posts: 17
Why do you want to use the main as the clearing device? My guess is that the numbers came in high using the upstream device and that interfers with production/maintenance tasks. That was the case at my facilities (generation), so the engineers convinced the management team that IEEE doesn't require that you use upstream (out of the box) protection, either method is allowed. While I don't have access to the IEEE1584 standard an internet search leads me to believe that if your going to use the Local Main (in the box methodology) you need to determine if your gear is isolated, cubicle to cubicle. I don't think any manufacturer will go on record as such unless it's arc rated gear. The real ansswer is what method is safest for your worker and what other stratigies can you implement such as remote racking to protect the worker.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Switchgear Main CB used as Clearing Device
PostPosted: Tue Dec 30, 2014 6:01 pm 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1820
Location: North Carolina
Most common in industrial systems is to run from transformer secondary to panelboard/MCC. Primary side protection is limited at best for secondary side protection and is really just primary side short circuit coverage. At around 1000-1500 kva at 480-600 V, incident energy is well over 40 cal/cm2 for most facilities with a good, stiff primary side bus. So available PPE becomes the issue because the intended secondary side protection is integrated into the distribution equipment on the secondary side of the transformer. This issue does not arise at 4160 V or higher except with very large (over 10 MVA) transformers but by then, breaker dimensions at 2000+ A ratings with 20+ kA fault currents get so crazy expensive that it forces design decisions involving a more distributed (generator-style) circuit topology as a more cost effective approach that adds redundancy and inherently decreases incident energy to controllable limits for reasons other than arc flash. So the issue is generally only seen at low voltages or sometimes with high current radial or double ended feeds, not ring bus and not generally in medium/high voltage.


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