Intrinsically safe for Class 1 Div 1 Group D
Intrinsically safe for Class 1 Div 1 Group D
(OP)
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)
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)





RE: Intrinsically safe for Class 1 Div 1 Group D
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
RE: Intrinsically safe for Class 1 Div 1 Group D
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.
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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 h
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
RE: Intrinsically safe for Class 1 Div 1 Group D
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
RE: Intrinsically safe for Class 1 Div 1 Group D
Keith Cress
kcress - http://www.flaminsystems.com
RE: Intrinsically safe for Class 1 Div 1 Group D
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!
RE: Intrinsically safe for Class 1 Div 1 Group D
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
--www.calibrator.com--
RE: Intrinsically safe for Class 1 Div 1 Group D
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
RE: Intrinsically safe for Class 1 Div 1 Group D
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
RE: Intrinsically safe for Class 1 Div 1 Group D
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
RE: Intrinsically safe for Class 1 Div 1 Group D
One of those days...
John D
RE: Intrinsically safe for Class 1 Div 1 Group D
John D
RE: Intrinsically safe for Class 1 Div 1 Group D
Keith Cress
kcress - http://www.flaminsystems.com
RE: Intrinsically safe for Class 1 Div 1 Group D
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
RE: Intrinsically safe for Class 1 Div 1 Group D
You'd think an explosion would be an explosion no matter where you are in the world...
John D