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Class I, Div 1, groups A-F
"Explosion-proof" vs. Class I, Div 1 ...
By Mike Johnson on 4 June, 2002 - 10:18 am

If I took a device, say a transmitter, that is not rated for a Class I, Div 1 area and place it
in a explosion-proof enclosure/housing, will that make it pass for a Class I, Div 1 approved device
or does it have to be inspected by authorative body like UL or something? If a device is explosion-proof, does that make Class I, Div 1?
If a device is explosion-proof and only handles 120Vac, can that device be used in a Class I, Div 1 location?
Or does the voltage level do not matter as long as it is explosion-proof? If that is the case, then why use intrinsic safe circuits if being explosion-proof is all that is needed?

Mike Johnson

By Walt Boyes on 4 June, 2002 - 10:20 am

It's been done. It is also possible to install it in a purged housing, such as those made by Bebco and others. However, this gets into the area which is muddy and gray, called "designed to meet."

If FM or CSA or UL or BASEEFA approves the design, what comes with the approval is that their lawyers will defend you at their expense if it really wasn't explosion proof. That's why FM and the 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."

If you just buy a transmitter and stick it in a Nema 7 or Nema 9 enclosure, or the European or Asian equivalent, and it blows up the plant anyway, it's your neck.

Most manufacturers will not do "designed to meet" anymore, even though many would, up to the early 1990s, for this reason alone.

If you have any questions about what your employer would want you to do, ask first. One of the best defenses against damage suits is to blame the employee who did it, and fire that employee and blacklist that employee throughout the industry. So, unless you want a new career selling siding or venetian blinds, don't do it.

Walt Boyes

---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel"
www.spitzerandboyes.com
walt@waltboyes.com
21118 SE 278th Place
Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142
--------------------------------------------

Dear Mike,

I think Walt boyes has given the proper answer only thing remained to answer is why to use Intrinsic safe device ?
The answer is : For Exproof itm is written on the instrument " Isolate elsewhere before openng" which makes live maintance of the instrument
impossible. which is possible with intrinsic safe instruments. Again for intrinsic safe instruments energy level is below 1 w .which dosen't cause
any personal injury.

Amol Savant

By wlmostia on 4 June, 2002 - 5:07 pm

This comment about live maintenance of equipment in explosion-proof enclosures being impossible is incorrect. Common practice is to get a hot work permit or some times called a gas free permit which requires that the area be checked with a combustible gas sniffer to insure that no flammable gas concentrations are present before and during maintenance. A bit more involved but certainly possible.

Bill Mostia
===========================================
William(Bill) L. Mostia, Jr. PE
Partner
exida.com
Worldwide Excellence in Dependable Automation
wmostia@exida.com(b) wlmostia@msn.com(h)
www.exida.com
281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

Bill,

(tongue firmly in cheek)

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

Bruce.

By Bill Mostia on 14 June, 2002 - 3:04 pm

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
wmostia@exida.com(b) wlmostia@msn.com(h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

By Mike Johnson on 6 June, 2002 - 6:27 pm

I know he is right. Walt is dead right!!!! That is the answer I would expect. My point is that I think some people practice in this manner all the time. I need to investigate a little more but I really do think some people do this and gets approved like using a NEMA 4X enclosure with an automatic purging/pressurization or sticking a transmitter in a NEMA 7 or 9 enclosure. I feel that IS circuits are needed and devices in a Class 1 Div I Zone 0 or 1 type area is absolutely necessary in order to be sure that one is NOT delivering enough energy to ignite flammable vapors or gases that are present continously or may be there due to a leak or something.

Mike Johnson

By Mike Johnson on 4 June, 2002 - 11:46 am

I am not talking about a practice I want to do but about an existing practice. Would one use an instrument that takes 120Vac for power in a Class 1, Zone 1 area?
If the instrument was in a Nema 7 or 9 enclosure and did not offer instrinsic safe circuitry for
additional protection, would it be advisable to use this instrument in a Class 1, Zone 1 area?
As long as the instrument was in a NEMA 7 or 9 enclosure regardless of power
considerations,
an authorizing broad will approve this instrument for a Class 1, Div I , Zone 1
type location?
Would there not be a restriction on the power as well as the enclosure or at least consideration on what potentially the open circuit voltage or short circuit current for the device could be and will this cause enough heating to cause an ignition of the vapors or gases in a Class 1, Div I, Zone 1 area?

By Walt Boyes on 4 June, 2002 - 4:56 pm

I don't think you understand what I said.

If the instrument is not third-party approved for the specific hazardous area classification required to locate it in a particular area of the plant, it does not matter whether it is in a "explosion proof" enclosure (NEMA7/9) or not. It is not good practice to use that instrument in that location, and you, personally, can be found both civilly and criminally liable and face heavy fines and jail terms if the device causes an accident.

So don't do it.

Walt Boyes

---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel"
www.spitzerandboyes.com
walt@waltboyes.com
21118 SE 278th Place
Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142
--------------------------------------------

Thanks, Walt. Now I think we understand what you're saying... but that leaves me confused as to XP enclosures and wiring methods. NEC Art. 501
defines enclosure and wiring requirements for Class 1 Div. 1 and Class 1 Div. 2 areas. In both cases, it seems that code says I can use non-intrinsically safe devices as long as I am using XP or purged/pressurized enclosures, as well as a wiring method approved for the Class/Division area. Also, I had always thought that XP enclosures were intended to keep the explosion/conflagration *inside* the enclosure, not to necessarily eliminate any possibility of explosion. Are you saying that *merely* complying with the code is not sufficient to protect the engineer in a court case?

Paul T

By Bob Peterson on 5 June, 2002 - 9:45 am

> Are you saying that *merely* complying with the code is not sufficient to protect the engineer in a court case? <

The sad fact is that even being completely innocent is not enough to protect you in court. You need to keep in mind that you can be right but still go bankrupt if you don't have the funds to pay for the litigation. Lawyers are not cheap. Liability and malpractice insurance is not really about liability or malpractice. Its about having the wherewithall to defend yourself in court. And remember that even if you comply with exisitng codes today this does not guarantee that you will not be sued in the future over something you did today that does not meet the 2020 version of the code.

Bob Peterson

Well, yeah... I hear that. What's your interpretation of NFPA70 though? I have in the past bought transmitters, for example, that are sold... (listed? I can't remember if they were!) for use in Class/Division areas.

The only difference between what you get when buying it for a classified area vs. unclassified is the enclosure that it comes in, and then of course the wiring method you use to install it. So... how do we interpret NFPA70 when working in classified areas?

Paul T

By Bob Peterson on 6 June, 2002 - 1:48 pm

I am not all that sure that what you are saying about XP versus non-XP instruments is true. It may well be that additional issues above and beyond the enclosure itself have to be considered, especially the process connection
itself. Obviously the whole instrument cannot be put inside an XP enclosure and still have some way for the instrument to connect to the process. To make the process connection, some part of the instrument must be outside the XP enclosure, thus some part of the penetration of the XP enclosure is not made via a conduit seal, which is the only "legal" way to bring something
into the XP enclosure. And I am pretty sure the only thing the code allows you to bring into an XP enclosure is wiring, and then only through a seal.

OTOH - for something which can be completely enclosed inside the XP enclosure, with only wiring leaving the XP box through seals, it would seem to be a different case. Perhaps Walt could comment on this point since he brought up the point about "designed for" type equipment that is not actually listed.

A second issue is that AFAIK, OSHA requires you to use only listed devices in Division I (maybe even Division II) areas IF a suitable device is available. Thus if there is an listed XP device available for a specific use, using a "designed for" type device would not meet this requirement.

It really is not that big of a deal anymore. Just about anything is now available with the proper listing. In a few cases, you might end up having to use pressurization as a means of protection, and the Bebco systems are now listed, so you should be covered. OTOH - this is not so much an engineering issue as a legal issue. You never know what some legal weasel will convince
a jury of 20 or 50 years from now.

Best approach is to avoid the issue as much as possible. With some thought you can often locate things in non-hazardous or Division II areas instead of putting them in Division I areas. This is really the best solution.

BTW - want to make yourself nuts? I am told UL refuses to list cable seals for use in Division I areas. The code allows the use of cable in a few cases in Division I areas, but to my knowledge, NO ONE makes a listed cable seal to run the cable into the XP box. A couple companies sell them, but they do not carry UL listings. In fact, as I understand it they are an assembly consisting of a standard seal coupled with a standard cable bushing to protect the cable where it enters the seal. The assembly comes with a special tag on it noting that the assembly is NOT listed, even though the seal itself has a UL listing on it.

Bob Peterson

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

1 out of 1 members thought this post was helpful...

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)

Paul,

In the IEC world, you must first buy a certified explosion-proof enclosure. This has undergone tests for pressurisation and flame suppression - as an empty enclosure.

You can then put your equipment into it. This need not be certified.

You must then get the enclosure re-certified with the equipment fitted. This tests for things like pressure piling (the increased pressure from a
secondary explosion if gas or va;pour is forced into an isolated part of the enclosure before ignition, and probably more important temperature
rise. The empty enclosure has no surface temperature rating as that depends on the power dissipation of the contents.

I don't think things are that different in the US..
Cheers,

Bruce.

By wlmostia on 7 June, 2002 - 2:55 pm

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
wmostia@exida.com(b) wlmostia@msn.com(h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

1 out of 1 members thought this post was helpful...

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)

By Walt Boyes on 5 June, 2002 - 10:09 am

Yeppers. That is exactly what I am saying. That is why NO company supplies standard area classification equipment simply installed in NEMA 7 or NEMA 4/7 or NEMA 7/9 enclosures.

That's why positive purge systems have such a bad name UNFAIRLY I MIGHT ADD...I don't want the Bebco's and the other purge system makers mad at
me...and I believe that at least Bebco has gotten FM or UL approval on their systems.

In the 1980s and 1990s, it was quite common to see "designed to meet Class I Div 1, Groups C & D" on instruments. They'd be in a Crouse-Hinds or Adalet or Whoever enclosure, and while the instrument itself _might_ be FM approved in another enclosure, and the NEMA 7 enclosure itself _might_ be approved, in the early 1990s, FM took the position that putting an instrument into an approved enclosure voided the approval of the enclosure, and therefore the configuration itself had to be approved.

QED.

Walt Boyes

---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel"
www.spitzerandboyes.com
walt@waltboyes.com
21118 SE 278th Place
Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142
--------------------------------------------

By Mike Johnson on 6 June, 2002 - 1:50 pm

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.
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.

Mike Johnson

By wlmostia on 7 June, 2002 - 2:08 pm

> 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
wmostia@exida.com(b) wlmostia@msn.com(h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

By Mike Johnson on 7 June, 2002 - 2:10 pm

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

By Bob Peterson on 6 June, 2002 - 6:39 pm

Just out of curiousity, what can you put in an explosion proof enclosure if not general purpose equipment? I tend to concur that just putting an instrument inside an XP box is probably not such a great idea since the process connection is an issue. I would not trust such an arrangement.

However, there does not seem to be a good reason why one could not put general purpose equipment (say an LED display) inside an XP enclosure, where all the entries are sealed. In this case, FM's position seems to defy logic.

Bob Peterson

By wlmostia on 6 June, 2002 - 6:44 pm

You are changing tracks on us. Now we are talking about Zones.

> I am not talking about a practice I want to do but about an existing practice. Would one use an instrument that takes 120Vac for power in a Class 1, Zone 1 area?<

Yes if the equipment is approved for a Zone 1 Area or is rated for Division 1 area(NEC Article 505-20(B) Exception #1).

> If the instrument was in a Nema 7 or 9 enclosure and did not offer instrinsic safe circuitry for additional protection, would it be advisable to use this instrument in a Class 1, Zone 1 area?<

I don't understand the question. Why would you even want additional protection in a Zone 1 area?

Anyway NEMA 7(indoors) per NEC Article 505-20(B) Exception #1 can be used in a Class 1, Zone 1 area but not NEMA 9. NEMA 9 is dust-ignition-proof not explosion-proof.

> As long as the instrument was in a NEMA 7 or 9 enclosure regardless of power considerations, an authorizing broad will approve this instrument for a Class 1, Div I , Zone 1 type location?<

One cannot judge what ever an "authorizing board" is will approve but the answer would be the same if you are talking about the authority having jurisdiction as they have the final word and they are occasionally finicky but if they follow the NEC NEMA 7 should be ok indoors but not NEMA 9 at all.

> Would there not be a restriction on the power as well as the enclosure or at least consideration on what potentially the open circuit voltage or short circuit current for the device could be and will this cause enough heating to cause an ignition of the vapors or gases in a Class 1, Div I, Zone 1 area?

I'm not sure where this obsession with voltage and power is coming from but look at any major supplier of explosion-proof hardware(Crouse-Hinds,
Killark, etc) and you will see 240v, 277v, 480v and 600v rated equipment.

Give me a call and I give you a few minutes of free consulting and maybe we solve whatever problem you have been talking about or talking around.

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

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
wmostia@exida.com(b) wlmostia@msn.com(h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

By Bob Peterson on 4 June, 2002 - 1:27 pm

In a message dated 6/3/02 2:55:33 PM Central Daylight Time, mcj@DESMETUSA.COM
writes:

> If I took a device, say a transmitter, that is not rated for a Class I, Div 1 area and place it
in a explosion-proof enclosure/housing, will that make it pass for a Class I, Div 1 approved device<

Generally yes, however its probably not all that practical since you would not be able to make a process connection since anything coming into the
explosion proof enclosure must pass through a seal. Best to buy as an assembly.

It could also be Class II.

> If a device is explosion-proof and only handles 120Vac, can that device be used in a Class I, Div 1 location? Or does the voltage level do not matter as long as it is explosion-proof?<

Voltage level is not an issue. Whatever explosion proof apparatus you want to use must be suitable for the area classification. Your area
classification also denotes what group it is as well (A/B/C/D). Your apparatus also has to be suitable for the group as well as being labeled
Class I, Division 1. The group denotes the specific explosive gas that might be present. Many times equipment is rated for group C and D but not for A and B.

> If that is the case, then why use intrinsic safe circuits if being explosion-proof is all that is needed?<

IS circuits are inherently power limited (they can only deliver less energy to the field device than what would be required to generate a spark). Thus IS circuits are not something you can use in a situation where any significant power is required (such as a motor).

IS circuits are generally far less expensive than an equivalent explosion proof system. They are also probably somewhat safer, and a whole lot easier to deal with.

This is not something you want to make design decisions on without knowing a whole lot more than what you can learn on a mailing list. I suggest you acquire some books on the subject and reading them. Start by reading the sections in the NEC (and a good NEC handbook) that deal with hazardous areas.

Pressurization is another means of protecting against ignition of hazardous gases. You can also locate a general purpose device in a non-hazardous (or sometimes a Division II) area and avoid the issue altogether.

Bob Peterson

By Mike Johnson on 6 June, 2002 - 1:41 pm

I do not expect to learn anything from a mailing list. I am asking for opinions on a subject matter. Also the title of this E-mail should be Class I, Div 1, Groups B-D, Zones 0 and 1 for locations inwhich Flammable gases or vapors are present continously or sometimes.

By Bob Peterson on 6 June, 2002 - 7:43 pm

Class I, Div 1 is a US protection scheme. Zone 0 and 1 are the European scheme. You can't really mix the two, although a few devices I have seen
lately are dual rated as class I div 1 (explosion proof) and EExd (flameproof). BUT, I do not believe you can use flameproof enclosures in a
zone 0 area.

Bob Peterson

By wlmostia on 7 June, 2002 - 2:25 pm

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
wmostia@exida.com(b) wlmostia@msn.com(h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

By wlmostia on 6 June, 2002 - 6:05 pm

Only Groups A-D fall into the Class I category(explosion-proof) while Groups E-F, actually E-G, are Class II groups(Dust-Ignition-Proof).

> If I took a device, say a transmitter, that is not rated for a Class I,
> Div 1area and place it in a explosion-proof enclosure/housing, will that
> make it pass for a Class I, Div 1 approved device or does it have to be
> inspected by authorative body like UL or something?

Yes you can without specific approval or inspection of a National Recognized Testing Laboratory(NRTL) but it must be acceptable to your local authority having jurisdiction. It is, however, necessary as with all hazardous area
equipment that you maintain the explosion-proof integrity of the enclosure per the manufacturer's specification, the NRTL's rating for the enclosure, and meet any appropriate requirements of the NEC.

If only wires come into or out of the enclosure, then it should not be any problem, this is done all the time.

If you bring a flammable material into the enclosure, that a whole another ballgame. For this type of application, you must as a minimum maintain the explosion-proof integrity at the entrance of the flammable material, at the exit if there is one, and also the internal integrity must be considered. In general, I would not recommend that a user do this and if you are a manufacturer and you bring a flammable gas into the enclosure( for example, an analyzer), I
would certainly recommend that you have it approved.

> If a device is explosion-proof, does that make Class I, Div 1?

No! Traditionally(and occasionally still), an "explosion-proof" rating in a manufacturer's spec meant only Class I, Group D, Division 1. You can only use an explosion proof enclosure for specific area that is has been rated (approved/listed) for plus a few exceptions allowed for by the NEC.

> If a device is explosion-proof and only handles 120Vac, can that device be
used in a Class I, Div 1 location?
> Or does the voltage level do not matter as long as it is explosion-proof?

Explosion-proof does not depend on voltage level but the NEC requires that you use appropriate equipment for the voltage level you use. Generally, a standard explosion-proof enclosure would be limited to 600 volts or less.

> If that is the case, then why use intrinsic safe circuits if being
> explosion-proof is all that is needed?

Intrinsic safety is a different type of protection method. Intrinsic safety is a low voltage, low power method and 120 vac stuff, motors, and other high voltage/high energy stuff cannot use it. Where both are applicable, there
are proponents of the use of both methods. In the US, intrinsic safety is not nearly as popular as in Europe. This is probably because explosion-proof has historically been the method of choice in the US, 80% of the US is Division 2, and it is generally easier to apply but these are obviously not the only reasons one might consider the
selection of a protection method and intrinsic safety certainly has its merits. One must pick the protection method appropriate for the application and the overall environment that it is installed in.

I suggest that you consider reading Ernest Magision's book "Electrical Instruments In Hazardous Areas, 4th Ed" from ISA, ISBN: 1-55617-638-4. Another good book is "Electrical Installations in Hazardous Locations," by Peter Schram and Mark Early, from NFPA, ISBN: 0-87765-356-9.

Let it be clear that engineering and installing systems in hazardous areas is not for the un-informed and while getting a clarification of something from a mailing list or getting resources or references is reasonable, getting basic knowledge or expertise from a mailing list is flat dangerous.

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

By Mike Johnson on 7 June, 2002 - 10:13 am

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.

By Davidb@teco-inc.com on 7 June, 2002 - 3:53 pm

"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.

By Phil Corso, PE on 11 June, 2002 - 9:17 am
1 out of 1 members thought this post was helpful...

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

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

By mcj@desmetusa.com on 17 June, 2002 - 11:59 am

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?

By mcj@desmetusa.com on 17 June, 2002 - 12:25 pm

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.

> 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
wmostia@exida.com(b) wlmostia@msn.com(h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

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
wmostia@exida.com(b) wlmostia@msn.com(h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

By Estellito Jr. on 23 July, 2003 - 11:27 pm

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