# Opening MCCs in Hazardous Environments



## Fixastang (Sep 4, 2012)

I work in a WWTP where we are establishing a new Arc Flash policy. We have two buildings which are require explosion proof fittings and wiring procedures due to the methane and other explosive gases which could be present in the air. Currently, no real procedures exist for the workers to follow regarding working in this type of environment. I have limited experience working in areas of this type and was recently approached with safety concerns regarding allowing the Thermal Imaging person to open energized starter enclosures in these two buildings. I asked the person to forego the inspection due to not having a good answer on how it should be done. 

Can anyone make a recommendation where I could go to get more information regarding working on equipment in hazardous locations such as these?

Thanks.

Kurt.


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## glen1971 (Oct 10, 2012)

Pretty much any electrical apparatus that I've ever worked on in a hazardous location has the disclaimer on it that the area has to deemed safe with no gas in the area, before opening the covers, doors, etc.. X-proof MCC's would be no exception.. The only thing is that you'll be exposing the live parts and won't know of any potential arc flash situation until the box is open...


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## telsa (May 22, 2015)

You need to immediately contact experts within the coal mining industry.

They have faced this situation for decades and have the rules, techniques and equipment to deal with explosive gases.

There is absolutely nothing that you are facing that has not been tackled by the coal mining industry.

Joy mining equipment -- in particular -- uses medium voltages.

You'll need to install methane sniffers -- for starters.


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## triden (Jun 13, 2012)

I doubt your MCC is located in the class 1 area. In an area such as the headworks (where the grit screen is located) you are probably dealing with Class 1 Div 1 equipment. The electrical room is most likely adjacent to the headworks and contains 'seals' to ensure that it remains as an unclassified area (aka no explosion dangers).


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## KennyW (Aug 31, 2013)

triden said:


> I doubt your MCC is located in the class 1 area. In an area such as the headworks (where the grit screen is located) you are probably dealing with Class 1 Div 1 equipment. The electrical room is most likely adjacent to the headworks and contains 'seals' to ensure that it remains as an unclassified area (aka no explosion dangers).


Agreed. You do not want mccs in hazardous locations, open or not.

Electrical room with sniffers, exhaust fans, and seals would be the normal thing.


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## wildleg (Apr 12, 2009)

You can probably get a reasonable safety guideline by contacting your local gas company, which should have the latest DOT guidelines.

when we worked in haz locations for the gas company, the procedures were pretty standard:

1) log in with security/sign on site log
2) write out a hot work ticket
3) write out a gas monitoring ticket showing gas monitor #/last calibration date
4) do a complete sweep of the haz location work area
5) set up the standing gas monitor
6) turn on wearable monitors (we used the personal clip on 4gas monitors so you knew whether the haz gasses were present as well as whether or not oxygen was present
7) perform work/clean up
8) re sweep work area (I think we were supposed to do this at regular intervals?)
9) sign all the BS paperwork and leave etc.

Of course, if there was an event, a near miss, an accident, there was a bunch of other paperwork/log that had to be done too (if the gas monitors recorded an event you had to log that too or get in hot water).

hope that helps


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## glen1971 (Oct 10, 2012)

triden said:


> I doubt your MCC is located in the class 1 area. In an area such as the headworks (where the grit screen is located) you are probably dealing with Class 1 Div 1 equipment. The electrical room is most likely adjacent to the headworks and contains 'seals' to ensure that it remains as an unclassified area (aka no explosion dangers).


I've only worked in one area that they considered it an "MCC" and there was a crap load of Class 1 Zone 1 rated starters. 3' high starters with covers that sometimes needed 2 guys to spin the covers off because the last guy couldn't be bothered to use STL.. That part of the plant has now been recycled and is growing grass as we speak.. There are still a few of that style of starter around in service...

Manual motor starters, control cabinets, breaker panels, PLC cabinets, etc that are installed in a hazardous area need to ensure proper gas testing is done prior to removing the covers..


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## AK_sparky (Aug 13, 2013)

Another option for thermal imaging is something like this:

http://www.flir.com/instruments/display/?id=50386

Different manufacturers make them in different sizes and ratings.

But I would suggest chasing all the options mentioned by others in this thread first.


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## JRaef (Mar 23, 2009)

I too am interpreting the use of the term "MCC" to mean a motor control _*rack *_of individual NEMA 7 explosion proof enclosures, like in the picture below. Lots of people use the term "MCC" for these, even though MCC for the rest of us is a different thing and can NEVER be used in a classified area.









Yes, IR inspection windows are the only viable option for explosion proof enclosures. There is NO safe way to do a thermal scan otherwise. You CANNOT EVER open those enclosures when energized, and if it is the bolted flange type, by the time you de-energize it and get all of the bolts off, any thermal scan is meaningless.

The Flir units in the link above are intended for Arc Flash safety and go in standard NEMA 1, 3R, 12, 4 enclosures. Those are not explosion proof. It's not a simple thing to put them in NEMA 7 enclosures, because the enclosure doors have to be drilled and tapped to accept them. But it's the only way. The enclosure windows for NEMA 7 enclosures look like this:











What I've done for retrofit is to buy replacement doors for existing enclosures that have the windows installed at the factory. That way in the field, you just swap them out in a short amount of time. You can't cut and thread those holes in the field very effectively, so to remove the doors and take them to a machine shop means a days-long shutdown and would likely cost a lot more for that reason than buying replacement doors.


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## triden (Jun 13, 2012)

There is no way a municipal WWTP has the budget for Class 1 MCC enclosures. If they did, I would be shocked. I could see it in a mine site or an oil site, but not a WWTP.


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## chrisfnl (Sep 13, 2010)

Mix of good and bad advice in the replies...

First, you need to identify, is it actually a hazardous area? If so, what type of hazardous area?

I stress that you need to identify if it's a hazardous area, because even if you have a facility that produce an explosive environment, not all places in that environment are hazardous areas... Typically, the best and cheapest trick to get around hazing to install hazardous area equipment is to move the equipment out of the hazardous area.

It may be managed in the design through distance, positive or negative pressure, or even just by closing the doors.

If the equipment is installed in a safe area, the seals installed on conduit may only be there to keep the gas out. If so, normal arc flash precautions need to be taken.

If the equipment is actually installed in a hazardous area, there's still options.

Hazardous area equipment, regardless of type, is not to be opened live (some even come with special instructions to wait a period after isolating to allow self discharge of capacitors) under normal conditions.

Can the process that produces the gas be shut off? If so, can you conduct gas testing after to confirm the lack of a hazardous atmosphere?

There's all sorts of standards written on this already (you'll find the iec standards in the 60079 series).

Anything involving coal mining isn't relevant, unless you happen to be mining for coal, you're likely looking for information on a class 1 environment for the surface industry.

If you want to give more details, I can point you further in the right direction.


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## JRaef (Mar 23, 2009)

triden said:


> There is no way a municipal WWTP has the budget for Class 1 MCC enclosures. If they did, I would be shocked. I could see it in a mine site or an oil site, but not a WWTP.


I forgot he had said it was a "brown trout farm", so you make a good point. But in case you didn't know, all areas where wastewater is handled and exposed are Class 1 Div. 1 areas. Places where the wastewater is pumped and enclosed in pipes or in tanks, where the pipes MAY burst of there is a loss of containment, are considered Cl. 1 Div. 2. So wet wells are often considered C1D1 up to the rim, then C1D2 in the immediate vicinity.

But to your point being valid, what MOST facilities do it make sure the electrical gear is located _*out *_of the classified areas, because you are right, they generally would not have the budget to use NEMA 7 gear. That makes it more critical for EVERYONE involved to understand EXACTLY what you are dealing with. If the OP is ASSUMING that the standard NEMA 1 MCCs are located IN a classified area, that may be the source of the problem right there. They probably are not.


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## Fixastang (Sep 4, 2012)

JRaef said:


> I forgot he had said it was a "brown trout farm", so you make a good point. But in case you didn't know, all areas where wastewater is handled and exposed are Class 1 Div. 1 areas. Places where the wastewater is pumped and enclosed in pipes or in tanks, where the pipes MAY burst of there is a loss of containment, are considered Cl. 1 Div. 2. So wet wells are often considered C1D1 up to the rim, then C1D2 in the immediate vicinity.
> 
> But to your point being valid, what MOST facilities do it make sure the electrical gear is located _*out *_of the classified areas, because you are right, they generally would not have the budget to use NEMA 7 gear. That makes it more critical for EVERYONE involved to understand EXACTLY what you are dealing with. If the OP is ASSUMING that the standard NEMA 1 MCCs are located IN a classified area, that may be the source of the problem right there. They probably are not.


JRAEF,

The building has NEMA 7 gear similar to what you show in your other post. The two main buildings in question have a direct feed of the MSB to a large junction box where the three phases each land on a multi lug junction terminal and are then fed out to each piece of equipment. This is an older installation that does NOT have the protected bus structure depicted in your photo. There are no NEMA 1 MCC buckets located inside the classified area. One question I have repeatedly asked our contracted Electrical Engineer is why we draw air into the building, as any hazardous gas would be drawn off the flow channel located below the building. I have suggested we attempt to pressurize the building, thereby blowing air into the channel and not bringing it into the building. I have received vague responses with promises to follow up, but have not heard back from him regarding this.

Some of the NEMA 7 gear we have are round pill style devices where the top and bottom unscrew separately to expose the contactor and associated wiring. Others do have the view port depicted in your other photo. However this view port allows us to see the digital readout for the ultrasonic unit mounted inside the NEMA 7 cabinet. 

As I stated in my original post, we are trying to develop a arc flash program that will address many of the current "best guess" practices that have been followed here for years. Oddly enough, the two buildings in question do not have permanent gas monitoring systems installed as they were not deemed to have enough continuous occupancy to warrant the expense. Workers enter and exit these buildings without utilizing any form of gas detection equipment as there has never been an accident in them.

I do appreciate everyone who has provided comments regarding this matter. I intend on searching the internet for more information on the Coal Mining Industry to determine if there is someone in Central Illinois I can contact to discuss this matter further.

Thanks again for the help.


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## Fixastang (Sep 4, 2012)

triden said:


> I doubt your MCC is located in the class 1 area. In an area such as the headworks (where the grit screen is located) you are probably dealing with Class 1 Div 1 equipment. The electrical room is most likely adjacent to the headworks and contains 'seals' to ensure that it remains as an unclassified area (aka no explosion dangers).


Triden, The two buildings in question were built on top of the influent flow channels and have bar screen devices installed to rake the oversized floatables out of the incoming sewage. The main power for these buildings comes straight from the MSB located out in the yard approximately 100 yds away from each building. This power is then routed through NEMA 7 devices similar to those depicted in JRaef's post.

We built a new plant in 2007 which does have the NEMA 1 MCC located in another part of the building with potting eyes installed in the conduit runs going the NEMA 7 equipment which is installaed in the hazardous locations. Unfortunately, the older plant was started in the 1920's and received various upgrades over the years which included installing NEMA 7 equipment in the two bar screen buildings. I realize this is unusual, but I understand they paid extra for the NEMA 7 equipment as space is at a premium a this plant site.


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## triden (Jun 13, 2012)

Fixastang said:


> Triden, The two buildings in question were built on top of the influent flow channels and have bar screen devices installed to rake the oversized floatables out of the incoming sewage. The main power for these buildings comes straight from the MSB located out in the yard approximately 100 yds away from each building. This power is then routed through NEMA 7 devices similar to those depicted in JRaef's post.
> 
> We built a new plant in 2007 which does have the NEMA 1 MCC located in another part of the building with potting eyes installed in the conduit runs going the NEMA 7 equipment which is installaed in the hazardous locations. Unfortunately, the older plant was started in the 1920's and received various upgrades over the years which included installing NEMA 7 equipment in the two bar screen buildings. I realize this is unusual, but I understand they paid extra for the NEMA 7 equipment as space is at a premium a this plant site.


Building on top of channels like this?










This is a project that I finished up two years ago that involved a Class 1 area at a WWTP. Nema 7 enclosures were limited to a few devices like the gantry crane, unit heaters, and some vendor equipment. Sometimes there is no way around it, but I have never heard of a NEMA 7 MCC in a WWTP. In this building there was an odour blower in the channels that would suck air out from above the waste water and send it outside through an odour bed before venting to atmosphere. This helps more than anything to reduce H2S and Methane in the building.

Now with you situation in mind, I would push for having at a minimum some LEL monitors installed inside the building if you are going to be opening energized enclosures. LEL sensors monitor flammable gas such as methane and can alert personnel if the area were to ever exceed hazardous levels (typically > 10%). I would feel comfortable opening an energised enclosure with the makeup air unit running and verified LEL levels - no other time would I ever open an energized enclosure. Keep in mind that LEL monitors need to be mounted near the top of the walls as Methane is less dense than air.

Depending on the operation of your plant, it may be very easy and non-intrusive to power down equipment before checking it as inflow buildings are usually gravity fed and don't need electricity to operate for short periods of time. Powering down the equipment also makes it harder to thermally check devices though...

Some Nema 7 equipment in my last plant:


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