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 Post subject: Arc Resistant Switchgear?
PostPosted: Thu Mar 13, 2008 10:14 am 

Joined: Tue Feb 26, 2008 10:30 am
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Location: Canada
What does arc resistant switchgear do with respect to mitigating arc flash hazards? I know, qualitatively it reduces the risk an an arc flash incident, but how may this be quantified with respect to calculating arc flash hazards?

For instance, if I have a switgear lineup that has an arc flash hazard rating of 10cal/cm^2 (level 3), and I replace the line up with arc resistance switchgear, what is the NEW arc flash hazard at the switchgear lineup in cal/cm^2? Surely, there must be a limit to how much energry it may divert from a worker in the event of an arc flash hazard?

Additionally, if someone were to say perform some live work on the exposed bus in the arc resistant switchgear how is there any arc flash mitigation?

Who certifies arc resistant switchgear to say that this switchgear is arc resistant? For instance I could install insulated bus in a switchgear lineup and call it arc resistant (but no arc proof) since there will always be some exposed area of buswork inside the switchgear that my present some arc flash hazards, granted i understand that arc resistant switchgear is designed to contain and expel the hot gasses associated with the explosion in a controller manner through a chimney or duct, but i would have still reduced the liklihood or an arc flash incident occuring my insulating the exposed live parts.

Am I correct in saying that arc resistant switchgear generally only provides protection for non-intrusive work (ie: work such as switching circuit breakers) where an individual is not removing the covers to do work? Addtinoally, does this mean, for tasks such as switching circuit breakers that for arc resistant switchgrear that the arc flash hazard has been reduced from, say 40 cal/cm^2 to 0 cal/cm^2?, even though the same may not hold true for such intrusive tasks as opening up the switchgear live to perform work?


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PostPosted: Fri Mar 14, 2008 6:23 am 

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Location: Spokane Wa
There is no certification for arc resistant gear, and there is no mitigation if they are working on a live bus.

The only thing that I can think of is when operating the breaker/switch/etc you are more protected since there is less likely hood of the door blowing off as the pressure is released more readily.

When you are doing your study there is nothing that you can assume when it comes to the type of work being done. There are already too many assumptions that you have to make, from fault level to operating conditions.


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PostPosted: Mon Mar 17, 2008 6:12 am 
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Location: St. Louis, MO
The standard for medium / high voltage switchgear is C37.20.7. This is just a testing standard to certify "arc resistant switchgear." I have heard that it is due to be updated soon to include low voltage switchgear.

I'm with bluenoser on this. If you calculate the energy levels, I don't know that you can reduce those levels by task. The NFPA does this in their hazard/risk categories, but I'm not a fan of this method. The calculated energy level is what it is. I would be reluctant to implement even internal policies that change with the type of switchgear, task, location, etc. If something does happen, and a fault occurs, the energy is still there. It just gets directed somewhere else.

You would need to make the decision based on your equipment, as well as size of the plant / workforce, and communication with the workforce.


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PostPosted: Sun Mar 23, 2008 7:17 pm 
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Neither NFPA 70E nor IEEE 1584 seems to address arc resistant switchgear, so technically there would be no advantage (from a liability point of view). However; my opinion is the fault resistant gear might preclude the need for "suiting up" if site policy is to suit up for switching operations. Also, if the fault resistant gear can have breakers withdrawn and inserted with the doors closed, it would seem this would avoid the need to suit up.

These are just opinions without having spoken to manufacturers etc.


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PostPosted: Mon Mar 24, 2008 9:47 am 
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As it presently stands, the 2009 NFPA 70E does make provisions for Arc Resistant Switchgear. Table 130.7(C)(9) / Hazard Risk Tables have a new equipment category for Arc Resistant Switchgear. Racking a breaker with door closed is category 0. They are addressing the advantages of arc resistant gear with the 2009 version. It seems like it took a while but arc resistant gear was pretty much unheard of by most back in 2003 when the 2004 edition was being finished. Of course this standard is not final yet and could possibly change but so far it looks like this is the route it will take.

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PostPosted: Mon Jun 02, 2008 1:18 pm 
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brainfiller wrote:
As it presently stands, the 2009 NFPA 70E does make provisions for Arc Resistant Switchgear. Table 130.7(C)(9) / Hazard Risk Tables have a new equipment category for Arc Resistant Switchgear. Racking a breaker with door closed is category 0. They are addressing the advantages of arc resistant gear with the 2009 version. It seems like it took a while but arc resistant gear was pretty much unheard of by most back in 2003 when the 2004 edition was being finished. Of course this standard is not final yet and could possibly change but so far it looks like this is the route it will take.


In the US it was not well know, nut in Canada it has been around for many years, I got to witness some testing in 1998 on ABB's version, pretty amazing stuff.


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PostPosted: Wed Jul 16, 2008 8:35 am 

Joined: Thu Jun 12, 2008 2:07 pm
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Location: SLC
Switchgear integrity

I have a related question,

I am looking at where to install IR viewing panes in the higher rated equipment, say category 3 or 4 or Dangerous. (I am not sure it's the best avenue yet but it's where I am at now)

Most of the panels on the switchgear either have vents (say the back panels) or there are holes for switches, meters, buttons, etc... I have been hearing that if the panel is cut to install the IR viewing pane that it will "decertify" the panel as far as UL listing is concerned. ? What is the difference in the holes and the installation of the pane vs the meters or buttons or switches?

The ways I have heard of to reduce the incident energy levels do not seem to be an option for me at this time...

Any clarification from you guys is greatly appreciated.


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PostPosted: Wed Aug 06, 2008 2:22 am 

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Infrared "Viewing Panes"

Bombo wrote:
I have a related question,

I am looking at where to install IR viewing panes in the higher rated equipment, say category 3 or 4 or Dangerous. (I am not sure it's the best avenue yet but it's where I am at now)

Most of the panels on the switchgear either have vents (say the back panels) or there are holes for switches, meters, buttons, etc... I have been hearing that if the panel is cut to install the IR viewing pane that it will "decertify" the panel as far as UL listing is concerned. ? What is the difference in the holes and the installation of the pane vs the meters or buttons or switches?

The ways I have heard of to reduce the incident energy levels do not seem to be an option for me at this time...

Any clarification from you guys is greatly appreciated.


Hi Bombo,

From your terminology I would say that you are considering a polymer product in your application.

The first advice I would give is consider this choice very carefully, the only product referring to itself as an infrared "Viewing Pane" is manufactured almost exclusively from plastic and has a thin film polymer optic - which is partially IR transparent - supported by a mesh grid. You must consider the reason you are installing this kind of product before making the choice.

For example, I would guess that since you are looking to install into the higher energy systems on your site, that you are concerned about arc-fault? If that is so, installing a product with a thin film optic that will fail under a fault condition is certainly not the way to go. In fact, it could be said that by installing a product that will knowingly fail under the duty it was installed to perform is actually in contravention of OSHA requirements - and hence illegal - as the injury caused as a result of a molten polymer (contact) burn would be worse than the radiant energy burn if the door were opened. :(

From a due diligence standpoint it would be good to consider the other options out there are there are IR Sightglasses/Windows that have been subjected to electric arc-fault testing and can provide protection. Two suppliers of this kind of product are SquareD and Hawk IR International.

As for retro-fitting, this is always tricky especially when UL are concerned. Some components do hold a basic retro-fit "option" when it comes to UL recognition and in most cases a field inspection from UL will not be nessecary. You should check with the Sightglass manufacturer about this. However a word of caution, if you are installing the sightglass/window/pane into your equipment then you must match the UL50/NEMA environmental testing certification of the product to that of the host equipment or you may indeed derate it. For example, my understanding is that both SquareD and Hawk IR have UL50 Type 3/12 certification for their ir window products and therefore can be installed into Type 3/12 equipment or less without derating the environmental integrity of the system. The only polymer viewing pane I know of CLAIMS to have NEMA 4 certification but in fact only holds UL50 Type 1 which means that if you install this product into any equipment with a UL50 rating of Type 1 or over then you will definately derate it. Don't be duped by terms such as "self certification" or "equivalent to European testing", if it is UL50 Type 1 then that is the only equipment type you may be able to install into. If there is a subsequent UL field inspection and a Type 1 product is installed into Type 3/12 equipment I am almost sure you will get a non-compliance for the installation.

Additional points to consider when installing the product type is Grounding as part of the installation. UL recently released a standard - UL50V - which effectively states that polymer infrared pane type product which, by virtue of their design, have floating metallic components - such as the cover retaining screws - must have supplemental Grounding installed as part of their installation. A sensible precaution but something that the manufacturer might not tell you as it will increase the overall "installed cost" of the product as an Earth Loop Impedance check must be performed with calibrated equipment to check the Ground installed. Some infrared sightglasses use a design called autoground which means that the whole product is Grounded as part of the installation, something that saves a considerable amount of time and hence reduces the installed cost even though the initial unit cost of a polymer unit maybe less.

Bottom line is be diligent and sure of what you are told, ask for certifications and pose the questions that will show that you have excercised the maximum diligence before choosing your product. If the manufacturer cannot provide the data you are asking for, my advice would be to move on to another.

Hope this helps!


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PostPosted: Wed Aug 06, 2008 6:04 am 

Joined: Thu Jun 12, 2008 2:07 pm
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Location: SLC
InfraredMan wrote:
Hope this helps!


Hey, thanks InfraredMan, yes it does help!

Yes my terminology on this is off, I meant exactly what you had said - the Sightglasses or windows, and I was thinking the ones by Hawk IR.

This would be retrofitting on installed equipment, so your info helped a lot.

Thanks


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PostPosted: Wed Aug 13, 2008 3:10 am 

Joined: Wed Aug 06, 2008 1:48 am
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Infrared Sightglasses

Hi Bombo,

Yes, the Hawk products are probably the best on the market.


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PostPosted: Mon Jul 13, 2009 9:28 am 

Joined: Mon Jul 13, 2009 8:55 am
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Allen Bradley Arc Shield

I have a quote for an AB 2100 MCC with Arc Shield for an MCC lineup. The AB rep says they are the only supplier of low voltage switchgear that meets IEEE C37.20.7 with type 2 protection. This supposedly gives increased resistance to Arc Flash failures on front, side and back of the MCC. The cost increase is from 22K$ to 25K$ (3K$ more) to get this option which includes spring loaded doors, Isolation barriers, and Automatic shutters.

The salesman says the IEEE standard was extended to low voltage gear in January.

This seems reasonable if it truly provides increased protection and perhaps some opportunity to shed the PPE quicker.

Anyone have any experience with this equipment?


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PostPosted: Tue Jul 14, 2009 5:03 am 
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IEEE C37.20.7 defines the requirements for arc resistant construction. The big change for 2009 was NFPA 70E. The Hazard / Risk Table 130.7(C)(9) lists "Arc-Resistant Switchgear Type 1 or 2" as Category 0 for operating or racking the CB with the doors closed.

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PostPosted: Tue Jul 14, 2009 5:39 am 
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Location: North Florida
I've personally had experience with some 15KV Arc Resistant Switchgear and arc flashes. In both cases, the arc flash was diverted out the upper chutes with only minor or no damage to the door and surrounding area. I took a look at the AB MV MCC's last year and was very impressed with the design. Even if it doesn't decrease the PPE level (which in the tables it does) it's still worth the extra $3K just for the decrease in damage it does to the area around the gear in the event of an arc flash.

I'm now a strong proponent of arc resistant switchgear and pretty much spec it out as a standard. I don't even let the purchasing guys see the option for non-arc flash so they don't see the adder. That's a small amount of money for the extra safety and better built equipment.

Just my 2 cents worth.

TxEngr


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PostPosted: Sat Feb 27, 2010 6:23 pm 
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Location: Cincinnati, OH
We have two lineups of Powell 38 kV arc resistant gear. The arc-resistant capability of both is UL listed - the first one we installed in 2005 was sent to UL for the testing so the product line could get listed. We had a CPT mounted inside the first lineup blow up and the gear worked as expected.

How the arc resistant characteristics affected the incident energy calculations is really irrelevant for us. For people that are used to switching 35 kV SF6 breakers from 100 ft away inside a building and operating switches with a 15 ft hot stick, the idea of being anywhere close to the breaker during racking or switching makes us uncomfortable. We have a mimic control panel at the end of the sub that is used for switching, and we have a remote racking operator for racking.

As someone else pointed out, the arc resistant capability is useless if you have to open the door to un-jam a racking mechanism. For this reason we haven't purchased 5 kV or 480V arc resistanct switchgear - I'd rather take the 15% cost premium and spend it on CTs, relays, and smart relay protection engineers.


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PostPosted: Wed Sep 01, 2010 8:09 am 
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I have heard about a ruling that supposedly went into effect on 1-1-2004 that any new switchgear rated at 1000 volts and above must be arc fault rated with integral grounding switches and viewing windows. Is there any truth to this or is it just 'urban legend'?


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PostPosted: Wed Sep 01, 2010 10:51 am 
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cbauer wrote:
I have heard about a ruling that supposedly went into effect on 1-1-2004 that any new switchgear rated at 1000 volts and above must be arc fault rated with integral grounding switches and viewing windows. Is there any truth to this or is it just 'urban legend'?


I don't think that is true, I think it remains an (expensive) option.


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PostPosted: Sun Sep 05, 2010 9:31 pm 

Joined: Mon May 03, 2010 1:41 am
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Our new (3rd) building is equipped with Arc resistant switchgear 15kV and low voltage. But another feature is the "Maintenance" mode kirk key that selects lower values for the trip relays. I do not have all of the specifics yet but it definately sound like a move in the safer direction.


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PostPosted: Mon Sep 06, 2010 7:17 am 
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Data Center Electrician wrote:
Our new (3rd) building is equipped with Arc resistant switchgear 15kV and low voltage. But another feature is the "Maintenance" mode kirk key that selects lower values for the trip relays. I do not have all of the specifics yet but it definately sound like a move in the safer direction.


Think you are confusing the arc flash reduction switch and the kirk key, 2 different things. The maintenece switch option is one of the most popular mitigation solutions for existing gear, we have done hundreds of retrofits or these, have about 20 in the shop right now in fact.


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PostPosted: Mon Sep 06, 2010 11:49 pm 

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Like i said, I don't have all of the specifics. I was told Kirk key. I just figured it was a key by kirk industries so that getting random duplicates is not easy. But it is definately for arc flash mitigation. However it is new gear and a new installation. We have many, many kirk keyed systems for prevention of tying systems together when they are out of sync, etc. (and i am not saying that someone didn't mispeak either). Heck it could be a Medico and someone is just calling it a Kirk key because that is what they are used to seeing on our switchgear.


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PostPosted: Tue Sep 07, 2010 5:58 am 
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Data Center Electrician wrote:
Like i said, I don't have all of the specifics. I was told Kirk key. I just figured it was a key by kirk industries so that getting random duplicates is not easy. But it is definately for arc flash mitigation. However it is new gear and a new installation. We have many, many kirk keyed systems for prevention of tying systems together when they are out of sync, etc. (and i am not saying that someone didn't mispeak either). Heck it could be a Medico and someone is just calling it a Kirk key because that is what they are used to seeing on our switchgear.


Likely it is something like this

http://www.utilityrelay.com/QUICK-TRIP_Page.html


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