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ekstra   ara
 Post subject: Lowering arc flash hazards
PostPosted: Wed Sep 29, 2010 6:13 am 

Joined: Tue Jun 08, 2010 12:11 pm
Posts: 3
Hi all,

I currently work at a production facility, and we have had two engineering firms provide us with short term, and long term recommendations to lower our category 4 and higher hazards, to category 2 or lower. We have implemented the short term solutions: remote actuators to open and close 480V breakers, and remote racking devices to remove and insert 480V breakers. Any other task requires the equipment to be de-energized.

Now on to the long term solutions, we will call it Phase 1. Both firms recommended maintenance switches, zone differentials, and zone select interlocking. We ruled out maintenance switches because of the interaction required by the E&I employee. I am familiar with differentials, but have no experience with zone select interlocking (ZSI). Does anyone have any experience with ZSI? Is it good or bad, do you recommend it?

Our Phase 2 plan is to reduce all category 3's to category 2 or lower. Most of our category 3's are at the MCC level. For those applications my thoughts are to use instantaneous settings on the 480V switchgear feeding the MCC. I know most people prefer not to use instantaneous because of the problems with motor starting, but I've been playing around on ETAP, and found I can lower most of the MCC's down to cat 2 by using an instantaneous setting that is about 2 to 3 times higher than the largest motors starting current. How do you all feel about using instantaneous settings? What are others during to lower the arc flash hazards at the MCC level?

One other question. Our corporate E&I team decided that we would establish arc flash reductions based on the task being performed. Example: If you were going to switch on a motor at an MCC rated 9 cals (Cat 2), if the door was closed and secured you could take an 8 cal reduction. Reducing the required PPE to a Cat 0. I hate this policy and don't agree with it all because the door in no way lowers the energy level. I understand what they are trying to accomplish but I see no merit behind it. Now my question is, has anyone seen other facilities do this?

I am done now.

Thanks,

Jared


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PostPosted: Wed Sep 29, 2010 10:26 am 
Sparks Level

Joined: Wed Jan 28, 2009 2:19 pm
Posts: 73
Location: Georgia
Welcome to the forum, Jared. Concerning your phase 1 question, I'll leave that for others who have experience with those types of devices.

Concerning your phase 2 plan to lower instantaneous trips on breakers feeding your cat 3 panels. We do this. It's sometimes a balancing act to reduce instantaneous and maintain coordination, but this is a valid mitigation technique.

As far as reducing PPE required based upon tasks (after the study has been done)...we don't do this. Like you said, the closed doors don't necessarily reduce energy levels.


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PostPosted: Thu Sep 30, 2010 5:25 am 
Arc Level

Joined: Wed Jun 04, 2008 9:17 am
Posts: 428
Location: Spartanburg, South Carolina
See http://static.schneider-electric.us/docs/Circuit%20Protection/Ground%20Fault%20Protection%20Equipment/0600DB0001.pdf for an explanation of zone interlocking.

Using an instantaneous setting without zone interlocking will generally eliminate selectivity. Compromises are often needed in protective coordination anyway.


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PostPosted: Thu Sep 30, 2010 4:07 pm 
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
Hard to generalize solutions, each system is differnt and will have different solutions. Adding ZSI to an existing system is an expensive solution and still presents some problems.


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PostPosted: Mon Oct 04, 2010 12:58 pm 

Joined: Tue Jun 08, 2010 12:11 pm
Posts: 3
Zog wrote:
Hard to generalize solutions, each system is differnt and will have different solutions. Adding ZSI to an existing system is an expensive solution and still presents some problems.


Could you please expand on the problems associated with ZSI.


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