It is currently Thu Feb 22, 2018 3:52 am



Post new topic Reply to topic Go to page 1, 2  Next
Author Message
ekstra   ara
 Post subject: MCC -Deenergized
PostPosted: Fri Dec 04, 2009 8:25 pm 
Offline

Joined: Fri Dec 04, 2009 8:15 pm
Posts: 27
Location: washington
Washington State and Company Electrical safety Policy state that no energized work be performed,in the definition deenergized is defined as being free from any source of electricity.A MCC bucket is therefore considered energized even though the bucket disconnect is open,it is still connected! The question is how can maintenance within the bucket enclosure be performed,tightening cleaning etc without out being considered energized?Working within the MCC bucket with door open would also be considered hazardous due to the potential of Arc Flash within the MCC center caused by a failure within an adjacent bucket.How does anyone deal with this situation?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Dec 04, 2009 8:32 pm 
Offline
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
Brodie wrote:
Washington State and Company Electrical safety Policy state that no energized work be performed,in the definition deenergized is defined as being free from any source of electricity.A MCC bucket is therefore considered energized even though the bucket disconnect is open,it is still connected! The question is how can maintenance within the bucket enclosure be performed,tightening cleaning etc without out being considered energized?Working within the MCC bucket with door open would also be considered hazardous due to the potential of Arc Flash within the MCC center caused by a failure within an adjacent bucket.How does anyone deal with this situation?


Remove the bucket. preferably by remote means.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Dec 04, 2009 8:44 pm 
Offline

Joined: Fri Dec 04, 2009 8:15 pm
Posts: 27
Location: washington
Not maintenance friendly

Removal of the Bucket,these are Large hard wired,Buckets with stab connections but also containing either VFDs or Soft Starters,ie Heavy,the work has been considered by others to be working on or near energized components ie the circuit breaker line connections so no PPE was worn,as the Circuit Breaker was at least 18" away from contact and also considered finger safe as the connections are recessed,what type of interpretation applies?-Buket removal HAZ Cat.-4


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Dec 04, 2009 9:49 pm 
Offline
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
this is a bit tricky but I understand the situation. The line side of the breaker or fuse remains live even with finger protection in place. You are trying to work on the bucket with the disconnect open. You are saying that you are NOT interacting with live parts because you are 18" away from the live part and have no need to work closer.

The problem is you have the doors open, and may be within the AF boundary. This is where the NFPA guys put on their jackets and ties, and go for a 3 martini lunch! While you are left trying to keep America's factories running.

Couple things I would say:

You need some type of arc flash attire. I would say at least Level 1 but maybe Level 2 without the flash shield, just safety glasses. Fash shield is recommended but I doubt the people doing the work will want it on for the duration.

Try running the calcs again for this situation but include the leads within the bucket that go from the stabs to the line side of the disconnect. Add the increased distance from the line side disconnect terminals to chest of the worker, which sound like it would be more than 18". This may drop you IE down to a manageable point. Restrict this work to only those who are trained on this special application. Record in your policy of this implementation.

This is not perfect but see if it helps.

Remember that NFPA 70E art 130 is not OSHA. OSHA says you can be cited for not having a plan in place and that conformance to art 130 meets that requirement. However, it would be splitting hairs to say you are NOT in compliance if you are following 99% of Art 130 but have to follow the 'general principle of what is trying to be achieved' with the 1% specific to your industry. Remember Arc 130 is in place because there are no industry guidelines to follow. You are the industry. Start documenting what you are doing with others in the industry so you have reference that it IS a norm within the industry.

Pulling the bucket, may in fact increase the overall risk to employees. I am always particularly concerned about installing buckets after being worked on.

I'm sure others will disagree, but in the field you sometimes have to adapt as best you can to compromise between the letter of the code and the intent of the code.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sat Dec 05, 2009 8:06 am 
Offline
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
Mark it on your calander Haze, I agree with you 100%.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sat Dec 05, 2009 11:38 am 
Offline

Joined: Fri Dec 04, 2009 8:15 pm
Posts: 27
Location: washington
MCC-Tricky Indeed

Zog and Haze-Thanks for your informative responses-Yes, typically safety glasses and daily clothing FR Shirt,Pants are worn while working within the Bucket,I have gotten EH&S involved in working on a risk assesment ,Job hazard analysis for the task.It is strange that at this Large facility the Arc Flash Analysis was performed several months ago,Ive seen the draft,yet it has not been stickered to date,One reason may be that several Circuit Breakers,including the ones serving thes MCC Buckets were listed as overdutied,not rated for AIC,it also was noted by me that the instantaneous trip was set to maximum -Example-150 Amp magnetic trip breaker serving a 75 HP motor was set at 1500 Amps,the starting current on the motor maxed out at 368 amps of course no selective coordination had been performed prior to the Flash Analysis,The MCC in its collective entirety was calculated to Category 3,I know the Engineering firm has reccomended Breaker replacement,although I now see this as a Code requirement not an optional couse of action,The biggest issue is that we are now an outsourced vendor performing work for a Company and using their safety program.Without specific adherence by the word-Deenergized-free from any source- is what it is.In the case of an injury me and my fellow workers might be asked what part of the practice did we not understand?It is so conveinent to write a policy which leaves the onus of liability on the worker who is trying to perform effective maintenance which is also required by NFPA 70 E while at the same time by the letter stating that the entire MCC be deenergized to perform maintenance,does this fall into the operational infeasibility wording?Unfortunatly this work had been going on for some years and it took a near miss,equipment failure, to wake me up to the potential danger I know it is creating a culturally paridim shift in thinking ,not always popular,but hey everyone gets to go home without being barbecued!


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sat Dec 05, 2009 1:13 pm 
Offline
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
Brodie wrote:
Zog and Haze-Thanks for your informative responses-Yes, typically safety glasses and daily clothing FR Shirt,Pants are worn while working within the Bucket,I have gotten EH&S involved in working on a risk assesment ,Job hazard analysis for the task.It is strange that at this Large facility the Arc Flash Analysis was performed several months ago,Ive seen the draft,yet it has not been stickered to date,One reason may be that several Circuit Breakers,including the ones serving thes MCC Buckets were listed as overdutied,not rated for AIC,it also was noted by me that the instantaneous trip was set to maximum -Example-150 Amp magnetic trip breaker serving a 75 HP motor was set at 1500 Amps,the starting current on the motor maxed out at 368 amps of course no selective coordination had been performed prior to the Flash Analysis,The MCC in its collective entirety was calculated to Category 3,I know the Engineering firm has reccomended Breaker replacement,although I now see this as a Code requirement not an optional couse of action,The biggest issue is that we are now an outsourced vendor performing work for a Company and using their safety program.Without specific adherence by the word-Deenergized-free from any source- is what it is.In the case of an injury me and my fellow workers might be asked what part of the practice did we not understand?It is so conveinent to write a policy which leaves the onus of liability on the worker who is trying to perform effective maintenance which is also required by NFPA 70 E while at the same time by the letter stating that the entire MCC be deenergized to perform maintenance,does this fall into the operational infeasibility wording?Unfortunatly this work had been going on for some years and it took a near miss,equipment failure, to wake me up to the potential danger I know it is creating a culturally paridim shift in thinking ,not always popular,but hey everyone gets to go home without being barbecued!


Ok, first off, please try using different paragraphs. I had to read that 4 times and still had a hard time following you.

If your available fault current exceeds your interuption ratings of your breakers the study is invalid for that device and you have bigger issues to deal with.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sat Dec 05, 2009 8:46 pm 
Offline
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
Zog,
I think my heart just skipped a beat!!


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sat Dec 05, 2009 9:08 pm 
Offline
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
Brodie,
A couple of things:

The CAT 3 is for the MCC as a whole, which is meaning the bus. In the bucket you have small wire leads that come off the stabs, and that short length will limit your fault current more than you realize. It would not take much to calc the IE on the load side of that wire, even if you just model it for the largest one, assuming no more than size 3 or 4.

In a combination starter that employees a breaker, that breaker usually only has an 'instantaneous' function to prevent false trips. The motor 'overloads' (also called heaters) provide the long time trip functions. Table 430.52 of the NEC sets the max limit for the size of the circuit protector versus the motor FLA. For instantaneous trip only breakers it is 800%. If its more than that then its not code compliant.

As far as the AIC of the breaker. You said they were 'overdutied' not sure what that means. They have to have a minimum AIC that will handle the fault current at that point. Again, the fault current 'at that point' is going to be less than the fault current at the bus. The breaker has to have some AIC rating you just have to find it or look it up. So tell the owner that there is a chance he may be able to solve two problems by doing the bucket calc, which may lower the IE for live work on an open bucket, and make his existing breakers now code compliant. Maybe!

Cat 3 on a typical industrial MCC, other than something huge, would imply to me that your overcurrent device has too much time delay. You are operating in the short time band of the trip. There are only limited reasons, like small MCC lineups with big big across the line starters - that you can't employ an Inst trip set on your MCC. I was running 800A feeders to a MCC lineup, that had Inst trip, and was starting a 300HP motor on a wye-delta starter. It never came close to drawing the 6500 amps needed to hit the Inst trip point.

A lot of times the company doing the analysis does just that - the analysis. The numbers fall where they may. A good analysis will also point out opportunities to reduce the IE. I've taken MCC's with a Cat 3 to a Cat 1, by changing a $1200 programmer on a switchgear breaker to one that only had 'short time' to one that had 'short time' plus Instanteous. That was two years ago and I talk to the electrician regularly - they've never tripped the breaker. And I knew they wouldn't. So there is lots that can be done.

As for the policy, written versus what you are instructed verbally, a hardbound log book that is used regularly and consistently can be submitted as evidence. So if you are placed in a situation that the owner commands you to violate his own policy - I would snap to attention, say "yes sir", then write down the request, date, name, reason, etc in my log book, don my FR, and do the work. You show up with your log book with 50 entries after someone is hurt, and you'd be glad you had it.

There is a good chance that the 'infeasible' definition may be applied to this company's MCCs. They just need to perform the analysis. There is nothing like having 3 or 5 engineers, ESHa, production people in a meeting, and have the notes of the meeting documented and added to the appendix of the Arc Flash Analysis Handbook to show why the conclusion was made. A lot of this is about following procedure and conforming to the intent of the code.

My 2 cents.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sun Dec 06, 2009 7:24 pm 
Offline

Joined: Fri Dec 04, 2009 8:15 pm
Posts: 27
Location: washington
MCC Buckets

Okay there is a motor overload it is not a heater type,but a current type set at 80 Amps,The main branch breaker is a Motor magnetic trip tpe ETI Siemens it has adjustable instantaneous settings.Current setting is 1500 Amps.

The AIC rating of the above branch feeder breaker is 35ka-The available fault current is greater than 35ka-Therefore the breaker has been reccommended to be replaced-Does this mean the study is invalid for this equipment?

I totally agree the inst.trip is beyond NEC code rquirements and in my opinion increases the Arc Flash potential at the Bucket.
Thanks for your input it is appreciated.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Dec 07, 2009 8:33 am 
Offline
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
Brodie wrote:
Okay there is a motor overload it is not a heater type,but a current type set at 80 Amps,The main branch breaker is a Motor magnetic trip tpe ETI Siemens it has adjustable instantaneous settings.Current setting is 1500 Amps.

The AIC rating of the above branch feeder breaker is 35ka-The available fault current is greater than 35ka-Therefore the breaker has been reccommended to be replaced-Does this mean the study is invalid for this equipment?

I totally agree the inst.trip is beyond NEC code rquirements and in my opinion increases the Arc Flash potential at the Bucket.
Thanks for your input it is appreciated.


If the study is assuming these breakers are clearing the faut then yes, your study is invalid. Depending on the breaker type upgrading may be easy, I can get you upgrades and maybe exchange credit for your existing breakers.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Dec 07, 2009 11:32 am 
Offline
Sparks Level

Joined: Wed May 13, 2009 3:19 pm
Posts: 56
Along the same lines of discussion…with regards to “energized troubleshooting” i.e. disconnect closed, which is done quite often, what do you all consider the starter buckets hazard level?

As discussed above the MCC Bus can be high but the buckets inertial protective device (MCB or fuse) can typically lower the HRC within the bucket to 0 or 1; if it’s considered. Our problem has been confidently taking credit for a device that is within the same “box” in which you are working. We’ve typically been letting the MCC HRC cover both the Bus and Starter Buckets. Comments?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Dec 07, 2009 6:50 pm 
Offline
Sparks Level

Joined: Sat Nov 21, 2009 10:23 pm
Posts: 73
Location: Ohio
SCGEng1 wrote:
Along the same lines of discussion…with regards to “energized troubleshooting” i.e. disconnect closed, which is done quite often, what do you all consider the starter buckets hazard level?

As discussed above the MCC Bus can be high but the buckets inertial protective device (MCB or fuse) can typically lower the HRC within the bucket to 0 or 1; if it’s considered. Our problem has been confidently taking credit for a device that is within the same “box” in which you are working. We’ve typically been letting the MCC HRC cover both the Bus and Starter Buckets. Comments?


There is absolutely no way you can consider the device within the same bucket. In addition, try a get a manufacturer to qualify (in writing) you using the main device (for mitigation) in an MCC - it won't happen.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Dec 07, 2009 8:19 pm 
Offline
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
No the study isn't invalid. Its just a matter of what 'node' is used to determine fault level.

Lets say that calculations reveal that the horizontal bus of the MCC comes out at 39KA RMS. Since the bucket breakers are 35K AIC, they are not suitalbe. Under that analysis they are not.

But, the 35K AIC breaker is not bolted to the horizontal bus. There is 14 inches of 1/0 cu xhhw cable that runs bucket stabs to the line side of the breaker. If you included this impedance of the cable, then fault current at the breaker lugs drops to 34.9KA. Now the 35K AIC breaker is adequate.

Most people do not split components down to this level, but there is nothing to say you can't.

If fault current now is 64.3KA, then I doubt the 14" of wire will get you where you need to be.

There are also other options to lower fault current. That may produce better benefits than upgrading all breakers to a higher AIC.

If the xfrm is old, replace it with one that has a higher impedance.

Install current limiting fuses in line to the MCC, or into the switchgear main. Current limiting fuses can substantially lower IE because of their fast clearly times, less than 1/2 cycle.

Install line reactors on the incoming cables or to the mcc's feeders to increase impedance.

I'm not saying you don't have to correct the problem that the Inst only trip breakers can not be higher than 800% FLA. All I am saying is to look at everything in its totality and then upgrade to get the most value.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Dec 07, 2009 8:24 pm 
Offline
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
I'd agree with Flash. You can't use the overcurrent device withing the bucket, to claim or calculate a lower IE due to that breaker clearing a fault. Insides of the buckets are very open, and the fault can originate or propogate to the load side of the OC device and thus have no effect. However, the OC always has 'some' cable impedance value that connects it to the bus and that impedance can be used to reduce IE - if the cable leave the bucket. If they also terminate to stabs on the back of the bucket with exposed terminations, then the cable can't be used because the arc could originate or propogate to that point. But, cable impedance can be used under both conditions to reduce fault current rating for the bucket OC device AIC.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Dec 07, 2009 8:53 pm 
Offline
Sparks Level

Joined: Sun Dec 23, 2007 1:44 pm
Posts: 348
Location: Charlotte, NC
"But, the 35K AIC breaker is not bolted to the horizontal bus. There is 14 inches of 1/0 cu xhhw cable that runs bucket stabs to the line side of the breaker. If you included this impedance of the cable, then fault current at the breaker lugs drops to 34.9KA. Now the 35K AIC breaker is adequate."

I personally think you are splitting hairs here. Would you really want to do this?

And rely on 14" of wire to save your butt, or someone else's! I hope not.

I have a max of 80% or rated that I have used for many years to begin to recommend equipment replacement. I try very hard not to ever allow any piece of equipment to get to 100% of rated.....but that is just my conservative approach.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Dec 07, 2009 10:18 pm 
Offline
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
haze10 wrote:
No the study isn't invalid. Its just a matter of what 'node' is used to determine fault level.

Lets say that calculations reveal that the horizontal bus of the MCC comes out at 39KA RMS. Since the bucket breakers are 35K AIC, they are not suitalbe. Under that analysis they are not.

But, the 35K AIC breaker is not bolted to the horizontal bus. There is 14 inches of 1/0 cu xhhw cable that runs bucket stabs to the line side of the breaker. If you included this impedance of the cable, then fault current at the breaker lugs drops to 34.9KA. Now the 35K AIC breaker is adequate.



Well, so much for agreeing with you Haze.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Dec 09, 2009 6:12 am 
Offline
Sparks Level

Joined: Fri Jan 16, 2009 1:07 pm
Posts: 67
Location: North Florida
Brodie wrote:
Washington State and Company Electrical safety Policy state that no energized work be performed,in the definition deenergized is defined as being free from any source of electricity.A MCC bucket is therefore considered energized even though the bucket disconnect is open,it is still connected! The question is how can maintenance within the bucket enclosure be performed,tightening cleaning etc without out being considered energized?Working within the MCC bucket with door open would also be considered hazardous due to the potential of Arc Flash within the MCC center caused by a failure within an adjacent bucket.How does anyone deal with this situation?


Is it possible that you are 'over reading' the definition? Using that definition, anything is still 'connected' even though the primary disconnect is still opened. So that means the entire MCC cannot be worked on even though the feeder breaker is opened since it is "still connected". That means you can never work on equipment unless the cabling is disconnected. Surely that is not what is meant by your employer and the State of Washington!

If you have opened the disconnect switch/breaker on the MCC bucket, and the line side of the switch/breaker is finger safe, then it is then safe to work in the bucket for tightening connections, installing control wire, etc. once the absence of voltage has been confirmed (wearing proper PPE).

As to the issue of adjacent buckets being energized: since there are no exposed electrical conductors and you are not interacting with the equipment in a manner that could cause an electric arc, then an arc flash hazard should not exist (read FPN #1 under the definitions for Arc Flash Hazard). This would allow you to work on the equipment. I would still wear PPE clothing for arc flash just to be safe, but I typically have my arc flash clothing on all the time anyway.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Dec 16, 2009 10:53 am 
Offline

Joined: Fri Dec 04, 2009 8:15 pm
Posts: 27
Location: washington
d. Exposure to unexpected electrical energy release that could result in electric shock or burns or in an explosion caused by an electric arc is covered by the standard for electrical safety-related work practices. Safeguarding workers from other hazards related to the unexpected release of hazardous energy during servicing and maintenance operations is covered by Part A-4.

Under WAC 296-24-975(l)(b), if the employer does not deenergize (under the circumstances permitted in WAC 296-24-975(l)(a)), then suitable safe work practices for the conditions under which the work is to be performed shall be included in the written procedures and strictly enforced. These work practices are given in WAC 296-24-960 and WAC 296-24-980.

Energized-

Connected to an energy source or containing residual or stored energy.

Completely isolate the machine or equipment from its energy sources using the appropriate energy-isolating devices after the machine or equipment has been turned off.

Deenergized is defined as being free from any sourc of electrical connection,in the case of an MCC Bucket it is considered energized until either the entire MCC is Shutdown or the Bucket is pulled free from the MCC .
These are the WA state definitions as well as the employers.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Dec 16, 2009 12:09 pm 
Offline
Sparks Level

Joined: Fri Jan 16, 2009 1:07 pm
Posts: 67
Location: North Florida
Brodie,

I did a quick check of WAC 296-24 (I didn't try to read the whole thing) and it is almost verbatum from the OSHA 1910 Subpart S. Under the definitions for Deenergized in OSHA (I couldn't find this in the definitions in 296-24) it says "Free from any electrical connection to a source of potential difference and from electrical charge; not having a potential different from that of the earth". So having the disconnect opened, locked and verified should meet this requirement.

The key to 296-24-975 is that electrical equipment shall be deenergized prior to working on it with exactly the same exceptions as in 1910 Suppart S and in NFPA 70E. It may be your employers interpretation that the entire MCC must be shut down to be safe and if so, you must follow their rules. It certainly is the safest way to handle this but is overkill in terms of performing minor work such as terminating cable in an MCC bucket.

The only time I de-energize the entire MCC to perform work is when removing or adding a buckeet to the MCC or when work is required on the incoming section. My breakers are finger safe and fully isolated allowing me to open the breaker/disconnect, lock and verify absence of voltage, and then perform work inside the bucket. But again, you must follow your employers rules.

TxEngr


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 27 posts ]  Go to page 1, 2  Next

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