Class I, Div 1, groups A-F

Well, it's not that bad. The cases I remember were pressure transmitters. The process connection was on the base of the transducer, and the "upper" part was the transmitter. I am thinking Bailey, for example- if you wanted the unit for a classified area, the housing that attached to the base was NEMA 7. If not, it was NEMA 1, or maybe nothing at all. Or another example is a TC or RTD, maybe in a thermowell. Again, for classified areas the top of the thermowell looked like something that belonged on a tank, for non-classified you might just have the top of the TC sticking out of a compression fitting (used to do a lot of TCs sticking out of compression fittings in my last job). You could then conduit (IMC or RMC... what fun!) the the top of the thermowell or the TC wire housing to your temperature transmitter, if you were using one, which again was in a cylindrical NEMA 7
housing with a top that screwed on and off. The jobs I used to deal with were Class 1 Div 2, and this was back in the early '90s, so things may
certainly be different now.

Does anyone on the list work in a process plant with classified areas? What is your plant practice for PT's, TT's, FT's, pH or ORP instruments, or anything else that may be in a classified area?

Paul T
 
I disagree with Paul T's statement that "... the only difference is the enclosure that it comes in..."!

Certification of Class I enclosures insures that effects of a possible explosion, resulting from the coincident occurrence of a flammable
air/gas mixture, and a source of ignition in the instrument's electrics (temp also), will not propagate to the surrounding atmosphere.

Breach of integrity of the path between the enclosure's interior and the ambient is obvious. So are leaks via electrical circuit paths into the
enclosure. But, the one that is frequently overlooked, is the path between the process and the instrument.

The difference between Div 1 and Div 2 is the based on the probability of the simultaneous occurrence of the factors mentioned above. For Div
1, the gas could be present frequently, even continuously. For Div 2, there is a lower probability of a flammable air/gas mixture, for
example, less than 1 hr in 10,000.

In conclusion, there is no doubt in my mind, that installation of equipment in x-poof enclosures should be left up to vendors having the requisite legal approval.

Search archives for my comments about our litigious society.

Regards,
Phil Corso, PE
(Boca Raton, FL)
 
M

Mike Johnson

Let us get some things straight.

1) I am NOT trying to get basic knowledge or expertise from a mailing list!!

2) I am NOT trying to put some electronic equipment into a NEMA 7/9 enclosure and call it ready for an area classified as Class I, Div. 1, groups A-D.

3) I made an observation about what others are doing, thought it was strange, and I decided to ask around about it.

I apologise to everyone if everybody thinks I am trying to put an UNAPPROVED PIECE OF EQUIPMENT INTO AN AREA THAT IS CLASSIFIED AS CLASS I,DIVISION 1,GROUPS A-D OR A CLASS II,DIVISION 1,
GROUPS E-F. THIS IS NOT MY INTENSION. ALSO, I AM NOT TRYING TO GET A FREE COURSE IN INSTALLING EQUIPMENT IN A HAZARDOUS AREA FROM OFF A MAILING LIST. I am sorry I even asked.
 
I'm not sure that I would agree with the statements regarding "FM and others have the good old fashioned collywobbles if you use the term "explosion proof" or "explosion safe". They use the term "nonincendive." They say that there is no such thing as "explosion proof."

It may be just a matter of semantics here but it is clear that FM uses the term "explosionproof" because they have a Approval Standard Class Number
3615 titled "Explosionproof Electrical Equipment General Requirements" which is used as an approval standard for approving explosionproof enclosures and other explosionproof equipment.

Nonincendive, on the other hand, has nothing to do with explosionproof and is a protection method for placing electrical equipment into Class I & II, Division 2, Class I, Zone 2 hazardous areas, and Class III Division 1 & 2. See the NEC Article 500.2 and ANSI/ISA 12.12.01 "Nonincendive Electrical Equipment for Use in Class I and II, Division 2 and Class II, Divisions 1 and 2 Hazardous(Classified) Locations."

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected](b) [email protected](h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.
 
> That is what I am talking about. Without naming companies, I have a position transmitter that is suppose to be able to use in a Class I, Div 1, groups C and D, but the only difference between it and one that is not to be use in a Class I, Div 1 area is the enclosure. They even print in the Spec/description under options " Enclosure for hazardous locations for Class I, Division 1, Groups C and D, or Class II, Division 1, Group E,F, and G" No where do they show UL or FM approval. As a matter a fact they show no approvals at all.<

It would seem that a simple phone call would clear this up and if the manufacturer cannot supply documentation as to the approval of the equipment then it is not approved/listed equipment.

If the manufacturer has purchased an explosion-proof enclosure in which they have installed a position transmitter and the installation does not violate the explosion-proof integrity then they acceptably may do so and be explosion-proof under the enclosure's rating. However, if the transmitter has a moving mechanical component or other sensing component that crosses the explosion-proof enclosure's wall, these must be rated explosion-proof where it enters the explosion-proof enclosure or in the case of wires meet the NEC requirements. The combining of approved/rated explosion-proof components is a perfectly acceptable practice and is done all the time.

In any case, according to the NEC, the local authority having jurisdiction has the authority to approve installations. In most cases, this means approval of hazardous area equipment by a Nationally Recognized Testing Laboratory (NTRL), ie FM, UL, ETL, etc.

In regards to meeting OSHA 1910.301-399 Subpart S Electrical, the authority having jurisdiction is
the Assistant Secretary of Labor for Occupational Safety and Health. And under this regulation Approved means:

"Approved. Acceptable to the authority enforcing this subpart. The authority enforcing this subpart is the Assistant Secretary of Labor for Occupational Safety and Health. "

and Acceptable means:

Acceptable. An installation or equipment is acceptable to the Assistant Secretary of Labor, and approved within the meaning of this Subpart S:

(i) If it is accepted, or certified, or listed, or labeled, or otherwise determined to be safe by a nationally recognized testing laboratory; or

(ii) With respect to an installation or equipment of a kind which no nationally recognized testing laboratory accepts, certifies, lists, labels,
or determines to be safe, if it is inspected or tested by another Federal agency, or by a State, municipal, or other local authority responsible for enforcing occupational safety provisions of the National Electrical Code, and found in compliance with the provisions of the National Electrical Code as applied in this subpart; or

(iii) With respect to custom-made equipment or related installations which are designed, fabricated for, and intended for use by a particular customer, if it is determined to be safe for its intended use by its manufacturer on
the basis of test data which the employer keeps and makes available for inspection to the Assistant Secretary and his authorized representatives. Refer to 1910.7 for definition of nationally recognized testing laboratory.

> Which seems to satisfy Art. 500-4 (a). I know I sound like a dumb ass, but it just seems like Art 500-4 (a) and (e) should be required for UL and FM approval. That way one can sure that the energy to the device is lower then what it will take to ignite anything and faults within the device is contained within the device.<

I don't know where your references are coming from(maybe the 1999 NEC?? which is out of date, and the 2002 NEC should be used). I'm not sure that I understand the first part of these statements. Are you saying the these articles should be required for UL or FM to approve something or that these articles require FM or UL approval?

In any case, see above in regards to required approvals.

In discussion of 1999 NEC Articles 500-4(a)(explosion-proof) and (e)(intrinsic safety), the purpose of intrinsic safety is to limit the energy to or in the hazardous area to below that which would ignite the most easily ignitable flammable mixture under normal and abnormal conditions. Explosion-proof's purpose is to contain any explosion that might occur inside the enclosure due to a flammable mixture getting into the enclosure and being ignited by an ignition source in the enclosure. Only one of the methods is required to meet Class I, Div 1 requirements. Either method can satisfy the requirements for Zone 1 but only intrinsic safety can be used in Zone 0.

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected](b) [email protected](h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.
 
M

Mike Johnson

Bill,
Thanks for your help but, I think I have caused enough confusion on this mail list.
So, I will stick to rereading NFPA 70 Art 500 thru Art 516, NFPA 36, and watch the "experts" at work. And maybe I will get over my idea of electrical energy, vapor pressure, temperature and enthalpy of reaction of a mixture of flammable vapors ( like hexane ) and the atmosphere at a given elavation within a plant that has such vapors present nearly all the time.

Thanks anyway and to all on this mail list
Good-bye
Mike Johnson
 
Paul... an example:

The HPI (Hydrocarbon Processing Industry) have long standing Standards that cover virtually every instrument installation known... even some
unknown!

IMO, Area Classification layout should be 3rd, immediately after Process Facility layout and an Electric (the only true science) layout!

If you, or others, don't agree, please don't send me typical Project Management Task lists that illustrate project execution sequence.

Regards,
Phil Corso, PE
(Boca Raton, FL)
 
This is not quite true. While the Zone scheme originated in Europe, it is now an acceptable area classification scheme for Class I areas in the US per NEC Article 505. While you cannot mix Division and Zone areas, they may exist in the same facility but may not overlap. Standard US equipment rated for Division can be used in US Zone areas per NEC Article 505.20. Note, however, European "EEx" and IEC "Ex" approved equipment are not allowed in American Zone areas, only "AEx" equipment. This is because some European and IEC hazardous area equipment do not meet the all American requirements for hazardous area equipment.

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected](b) [email protected](h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.
 
This is certainly not the case for the US. You can buy an explosion-proof box and install what general purpose or Div 2 area equipment you want in it or Div. 1 equipment on it and as long as you don't violate the explosion-proof integrity and approvals or operate in excess of a surface
temperature that a surrounding flammable atmosphere would be ignited by to your hearts delight. See NEC Article 500.2

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected](b) [email protected](h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.
 
"I am sorry I even asked"

I'm glad you asked. The amount of responses shows that this is a hot issue that should be discussed and is of interest to many of us.

David Bergeron, P.E.
 
B
Bill,

(tongue firmly in cheek)

is this because the physics of explosions or fires is somehow different in your part of the world?

Bruce.
 
P

Phil Corso, PE

To be technically correct, Class I includes Group A thu D. Mea Culpa!

Regards,
Phil Corso, PE
(Boca Raton, FL)
 
B
No, it is because of different protection philosophies(an example is cable vs conduit) which can lead to different constructions and in some cases, I believe, it is also due to how the testing and certifying is done.

The IECEx Scheme is scheme which appears to be the wave of the future whereby all hazardous area stuff would provide certification based on 1.)
one test 2.) one certificate and 3.) one mark.

For those interested, see -

"http://www.iecex.com/":http://www.iecex.com/

Bill Mostia
==================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected](b) [email protected](h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.
 
How does this imply that subsequent heating of enclosure from within the enclosure does not cause ignition on the outside due electrical heating causing convective heating on the inside to conductive heating of enclosure body to radiated heat on the outside surface to the world?
 
> Just because it is explosion-proof does not imply that the device can not act as a radiating heat source that could possibly cause ignition outside of the enclosure.<

FM's definition of explosionpoof enclosures from Approval Standard, Class Number 3615 is:

"Explosionproof(as defined by the National Electrical Code, ANSI/NFPA - 70) refers to equipment enclosed in a case which is capable of:

a) withstanding an internal explosion of a specified gas or vapor-in-air atmosphere;

b) preventing the ignition of a specified gas or vapor-in-air atmosphere surrounding the enclosure due to sparks, flashes, or internal explosion; and

c) operating at temperatures which will not ignite the surrounding classified atmosphere."

I think that Item "c" answers the question.

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected](b) [email protected](h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.
 
B
Bill,

The original comment that started this sub-thread was that, provided an enclosure is rated as "explosion-proof", any equipment can be fitted
inside. But how does the manufacturer of an enclosure know what an end-user is likely to fit into the enclosure?

Yes, the code as quoted does cover the case - but surely it is a bit unrealistic - or do UL/FM as part of their certification identify the
maximum power dissipation that the enclosure can handle?

Under the IEC codes there is also a concern about the effects of pressure piling within an enclosure if equipment is arranged so that the interior is divided into several sub-compartments. An enclosure in one can drive gas
into another compartment, then ignition from a higher initial pressure will create a pressure pulse that can be above the design capacity of the box.

As far as I am aware, neither in the US or in other parts of the world operating under the IEC-style rules have there been any major incidents
directly attributable to explosion-protected equipment failing, except for some explosions in non-sparking (Ex N) motors operating at high voltage. In our part of the world we have subscribed to both, with a lot of equipment
coming in to the country on skids made to US codes, and the main direction of formal requirements based on British /Australian /European codes. General consensus of electricians and technicians who have worked in the area is that the European stuff is generally easier to handle - after all, what can you do with a faulty conduit run that has seals everywhere but demolish the lot and rework from scratch?

Bruce.
 
> The original comment that started this sub-thread was that, provided an
> enclosure is rated as "explosion-proof", any equipment can be fitted
> inside. But how does the manufacturer of an enclosure know what an
> end-user is likely to fit into the enclosure?

This is a misconception that you can put anything in an explosion-proof box and it is acceptable in the area the enclosure is approved for. Going back to the NEC Article 500.2 the definition of an explosion-proof apparatus contains the following "... and operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby." Standard explosion proof boxes are designed to handle instrumentation, relays, contactors and such. The manufacturer does not know what will be put in their explosion-proof box but like everything else the user must properly apply the equipment they buy and install. If you are going to put something in an explosion-proof enclosure that has the potential of heating the external surface temperature to ignition levels then that shouldn't be done. This is part of the engineering of the installation. Designing of installations in hazardous areas require
consideration of many things not all of which may directly be covered in the codes.

> Under the IEC codes there is also a concern about the effects of pressure
> piling within an enclosure if equipment is arranged so that the interior
> is divided into several sub-compartments. An enclosure in one can drive
> gas into another compartment, then ignition from a higher initial
> pressure will create a pressure pulse that can be above the design
> capacity of the box.

I have heard of this concern internationally but not in the U.S. I believe that it is considered covered in the safety margins in the hydrostatic tests for the enclosure.

> As far as I am aware, neither in the US or in other parts of the world
> operating under the IEC-style rules have there been any major incidents
> directly attributable to explosion-protected equipment failing, except
> for some explosions in non-sparking (Ex N) motors operating at high
> voltage.

I am unaware of any incidents caused by properly installed and maintained explosion-proof equipment.

> In our part of the world we have subscribed to both, with a lot
> of equipment coming in to the country on skids made to US codes, and the
> main direction of formal requirements based on
> British/Australian/European codes. General consensus of electricians and
> technicians who have worked in the area is that the European stuff is
> generally easier to handle - after all, what can you do with a faulty
> conduit run that has seals everywhere but demolish the lot and rework
> from scratch?

I agree, explosion-proof conduit wiring means is difficult to work with once the seals have been poured.

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected](b) [email protected](h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.
 
E

Estellito Jr.

Mike,

If you place a device and place it in a explosionproof enclosure, you will need to have it inspected by authorative body, because it will be necessary to define the T rating of the complete mounting.
The voltage level doesn´t matter if you put in an explosionproof enclosure.
Intrinsic safe circuits have some advantages, as to be allowed maintenance "alive".

Estellito
 
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