Intrinsically safe for Class 1 Div 1 Group D

[zappedagain]

Hi,

Does anyone know where I can find the quantitative definition of "intrinsically safe"? I have a piece of equipment that I need to redesign to work in this environment, so I'm curious as to how close I am to meeting this requirement. I see a lot of fluffy definitions on the web. I'm looking for the appropriate standard (NFPA, NEC, etc.) where this is defined.

If you know of another forum where I should post this let me know and I'll move it over.

John (Z)

 

[itsmoked]

I don't believe I've ever seen specs for that.

The reason is that the barriers are the protection not really the device.

There are a few main concerns in an IS design meant to prevent circumvention of the barriers.

The general point is to remain below ignition temperature of the hazardous space flammable material.

If there are no storage abilities in the device you've done it. But if your device has a capacitor or an inductor then there is a curve (one for each) that denotes capacitance verse the voltage or current. As the voltage rises the allowed capacitance drops. For instance at 5V you could have something like 100uF but at 12V you can only have 1uF. (These are not the actual numbers!)

The same occurs with inductors but it's current based instead of voltage. X current allows up to Y Henries.

To limit current you can use a resistor. Except in IS applications no single point failure can cause a hazard. So if you need a resistor to limit current to an inductor, then you need to use two in series instead of one.


Now all you have to do is find those tables... I wish I knew where to find them.. I had a book with them at a previous job and since leaving the book was lost at that site. The designs were all done with the book opened to those two charts. Our designs all passed FM approvals.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[danw2]

Technical Report ISA–TR12.2–1995, Intrinsically Safe System Assessment Using the Entity Concept

pg 12: The Vmax and Imax values specified for a given intrinsically safe apparatus, taken together and compared to the ignition curves (Reference: ANSI/UL913), may fall in the ignition-capable area of the curve.
------------------
I assume from the reference that ANSI/UL913 has the ignition curves.

The ISA-TR12.2-1995 Intrinsically Safe System Assessment Using the Entity Concept costs $40

http://www.isa.org/Template.cfm?Sec...=/Ecommerce/ProductDisplay.cfm&ProductID=2885

References below are from the back of the Tech report above. Note the standards numbers. The Tech report is dated 1995, the area codes might or might not have changed since publication

Class No. 3610-1988
FACTORY MUTUAL RESEARCH CORPORATION (FMRC)
Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and II, Division 1, Hazardous (Classified) Locations
Available from: FMRC
1151 Boston-Providence Turnpike
Norwood, MA 02062
(617) 762-4300

ANSI/ISA-RP12.6-1995
ISA
Wiring Practices for Hazardous (Classified) Locations
Instrumentation, Part I: Intrinsic Safety
ISA-S12.1-1991 Definitions and Information Pertaining to Electrical Instruments in Hazardous (Classified) Locations
Available from: ISA
67 Alexander Drive
P.O. Box 12277
Research Triangle Park, NC 27709 Tel:
(919) 549-8411

ANSI/NFPA 70-1993 National Electrical Code®
NATIONAL FIRE PROTECTION ASSOCIATION (NFPA)
Available from: NFPA
P.O. Box 9101
One Batterymarch Park
Quincy, MA 02269-9101 Tel:
(617) 770-3000

ANSI/UL 913-1988
UNDERWRITERS LABORATORIES, INC. (UL)
Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1, Hazardous (Classified) Locations
Available from: UL
333 Pfingsten Road
Northbrook, IL 60062 Tel:
(847) 272-8800

 

[electrician1]

That is a type of protection that limits the energy available in the hazardous area to the level below that which could ignite a flammable atmosphere as itsmoked described.

2 types of barriers used in IS circuits:
Zener barriers and galvanically isolated barriers.
Zener barrier must have earth path .Standard permits an impedance to earth up to1ohm.For cross section of earth conductor need to use 2 separate 1.5mm² or at least one 4mm² copper conductor.
Components Exi “a” are allowed to be used in zones 0,1 and 2
Components Exi “b” are allowed to be used in zones 1 and 2
The minimum ingress protection for enclosures of IS circuits is IP20,glands should also be appropriate.
Inside JB clearance between terminals od IS and non IS apparatus bust be greater than 50mm.
The same distance need to be applied between AC power terminals and the module IS output terminals
Unused cable wires must be properly terminated on both sides or grounded on one side,screen to be earthed only on one side
IS circuit use voltages below 30V and 100mA
Devices which generate energy for instance thermocouple,photocell must not generate more than 1.5V ,100mA, 25mW.
You might find more information’s referred to following standards:
BS EN50020 protection by intrinsic safety
BS EN 60079-14 installation requirements

 

[itsmoked]

electrician1; Thanks for that run down.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

IEC 60079-11 : 2006 would be pretty definitive.

Intrinsic safety “i”
Type of protection based on the restriction of electrical energy within apparatus and of
interconnecting wiring exposed to the potentially explosive atmosphere to a level below that
which can cause ignition by either sparking or heating effects.

and

Intrinsically safe circuit
Circuit in which any spark or any thermal effect produced in the conditions specified in this
standard, which include normal operation and specified fault conditions, is not capable of
causing ignition of a given explosive gas atmosphere.




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If we learn from our mistakes I'm getting a great education!

 

[CharlieGill]

FM 3610 was the standard I always used in the US for designing IS instruments. It contains the curves for Emax vs C, Imax vs L, etc. It also covers spacing requirements and fault analysis. An IS circuit must meet the ignition requirements with one circuit fault (shorted trace, shorted component, open component, etc.).
I'm working on a job site so do not have my copy handy. If you need more information and are working to US design standards, I have an engineering friend that has more recent IS design experience than I have and can contact him for the most recent standards.

Charlie

Charlie
--

http://www.calibrator.com--

 

[zappedagain]

Thanks everyone! It looks like I have some reading to do, starting with FM 3610, or UL 913 and UL 60079-11 (IEC 60079)

My customer is requesting UL approval, although this may be generic 'safety approval'. Does anyone have experience with UL vs FM approval for Class 1 Div 1?

John

 

[itsmoked]

UL is a giant pain in the arse to work with. You are like a tail trying to wag the dog. Or, a peon trying to get royalties attention. FM is much more interested in your business.

It's my understanding that they are equivalent approvals and that no one is allowed to demand only one over another. But that's just my present understanding. It could be wrong.

We did an FM for C1D1 and it went smoothly.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[zappedagain]

CharlieGill,

I downloaded FM 3610 (for free from FM!) and I see that it defines the test, and references ANSI/ISA 60079-11 for the requirements.

I checked the Table of Contents for 60079-11 on the ISA web-site and I don't see anything that hints that it has the E vx C and I vs L tables.

ISA 60079-11 references ISA 60079-0, that does have a section titled "Annex B (normative) – Requirements for Ex components", so that could be the right document.

Please ask your colleague if that is the correct location to find the tables. I'm trying to avoid ordering a lot of standards that I don't need at this time ($$$).

Thanks,

John D

 

[zappedagain]

Or is it in 60079-11 Annex A (normative) — Assessment of intrinsically safe circuits? I looked right over that one. That makes more sense, as -11 is for intrinsically safe circuits; -0 is for general explosion proof requirements.

One of those days...

John D

 

[zappedagain]

I got my copy today and intrinsically safe circuitry (Rs, Ls, and Cs) is defined in 60079-11.

John D

 

[itsmoked]

Thanks zapped. Now I know where to find those dang tables!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[danw2]

60079-11 is IEC, not ISA.

ANSI/ISA–12.01.01–1999 Definitions and Information Pertaining to Electrical Apparatus in Hazardous (Classified) Locations references the IEC 60079-11 Intrinsic Safety, Type of Protection ‘i’, but I don't believe they contain the same material.

ISA 12.01.01 does not contain I vs L tables, for example.

Dan

 

[zappedagain]

That's true, and yes, it is quite a mess. The UL standards reference the IEC standards, not the ISA standards. They both have been discussed in this thread.

You'd think an explosion would be an explosion no matter where you are in the world...

John D