What is the voltage limit for requiring an intrinsically safe device on control wiring and motor voltages? This is in regards to a sewage lift station. There is 24VDC normally going to the floats monitoring the wet well level and to control the pump operation. We also have a SCADA/BYPASS system (in the lift station control panel) that we can switch to in the event the PLC fails to control the pumps. This system, at present, would then use 120VAC or 24VAC (depending on the lift station) float voltage to monitor the wet well level and control the pump operation. Articles 501 & 504 is the sections I have been trying to use as a reference.
Intrinsically safe wiring requirements for Class 1 Div2.
- Thread starter KrisED
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petersonra
Senior Member
- Location
- Northern illinois
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- engineer
there is no voltage limit. however as a practical matter, if it is IS wiring, it can't be 120 VAC since there are no IS barriers for that voltage level.
I am not even sure you can tap in downstream of the IS barriers with relay contacts or whatever you are using to isolate the circuit.
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- Mission Viejo, CA
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- Professional Electrical Engineer
If you have read Article 501 carefully you will find that intrinsically safe is not mentioned anywhere in it. For Class I, Division 2 you need to refer to Section 501.10(B)(3) and the various nonincendive definitions in Sections 100.2 or 500.2 (depending on NEC Edition), which reference ANSI/ISA-12.12.01 [20xx] -, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations.
Technically, voltage is only part of the "equation". Actually, total energy transfer the is issue as expressed by Minimum Igniting Current ratio (MIC ratio) and Minimum Ignition Energy (MIE).
While Article 504 is proper for intrinsically safe systems Section 504.2 will ultimately reference ANSI/ISA-RP 12.06.01-[20xx], Recommended Practice for Wiring Methods for Hazardous (Classified) Locations Instrumentation - Part I: Intrinsic Safety.
The basic rules are similar with lower acceptable MIC and MIEs.
And, in either case, don't forget your required manufacturer's control drawing.
Technically, voltage is only part of the "equation". Actually, total energy transfer the is issue as expressed by Minimum Igniting Current ratio (MIC ratio) and Minimum Ignition Energy (MIE).
While Article 504 is proper for intrinsically safe systems Section 504.2 will ultimately reference ANSI/ISA-RP 12.06.01-[20xx], Recommended Practice for Wiring Methods for Hazardous (Classified) Locations Instrumentation - Part I: Intrinsic Safety.
The basic rules are similar with lower acceptable MIC and MIEs.
And, in either case, don't forget your required manufacturer's control drawing.
Still confused
Still confused
:?Still confused:?. Do I need to have IS equipment for the float voltage and/ or motor voltages? There are properly installed seal-offs where the wiring leaves the wet well. Do the seal-offs satisfy the requirement for not needing IS equipment since any hazardous gases will not be able to enter the control panel?
Still confused
:?Still confused:?. Do I need to have IS equipment for the float voltage and/ or motor voltages? There are properly installed seal-offs where the wiring leaves the wet well. Do the seal-offs satisfy the requirement for not needing IS equipment since any hazardous gases will not be able to enter the control panel?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
you never "need" IS equipment. it is just one means of protection. other means are available such as explosion proof equipment.
as a practical matter, there is no way to use IS as a means of protection at typical motor voltages.
if the float switch in the wet well is protected by another means (such as explosion proof), IS would not be required for float switch wiring. just having seals does not cut it though.
Thank you petersonra.
This is an on going issue with the engineering firm doing our design work for our sewage lift stations. My point towards them "was why have IS equipment for float control voltages of 24vdc or 24vac, when you have a motor starter with 240 or 480vac in the same cabinet, coming from the same wet well", they're reply was "it is required due to NEC 70, section 504".
This is an on going issue with the engineering firm doing our design work for our sewage lift stations. My point towards them "was why have IS equipment for float control voltages of 24vdc or 24vac, when you have a motor starter with 240 or 480vac in the same cabinet, coming from the same wet well", they're reply was "it is required due to NEC 70, section 504".
Sierrasparky
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- USA
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- Electrician ,contractor
I have had this same concern and issue. I have also seen a manufactured cabinet without barrier for IS.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
If there is no barrier it is not IS.
There are a fair number of devices that have IS barriers built in so a separate barrier is not required. Generally the terminals for the IS wiring on such devices are blue in color and other terminals on the device that are not in the IS circuit are a different color.
It is also possible that the IS barrier is in a separate box located outside the main cabinet. I have seen this done where someone wants to provide a UL508a listing for the control panel. UL does not allow IS devices inside of a UL508a control panel.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I concur with petersonra's post #5 (you never "need" IS equipment). In fact, you never need an Intrinsically Safe System at all. Article 504 is simply one permitted protection technique among the many recognized in Section 500.7. While it has its own Article [504], it is never a requirement.
That said, your engineering firm should have been able to answer your original question. If they couldn't, they don't understand Intrinsically Safe Systems in the first place.
:thumbsup:
I was not aware of this - is this for barriers? for I.S. wiring and devices?
Would that mean it is not possible to put a AB Flex-Ex IO module or system into a UL508A panel?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Intrinsic Safety is a protection method for Class I Div 1 locations. It works for Class I Div 2 locations as well, but so does being nonincendive to begin with. There are some hoops to jump before you can decide a component non-incendive, but it is certainly better than having to go the whole 9 yards to make it IS with control drawings, etc. Voltage does not have anything to do with it. You could have a standard 480Y/277Vac 3 phase motor in a Class I Div 2 location, and that would be ok, but if you tried to put a 24VAC safety switch in the same space that would be forbidden without using some kind of protection method.
I've seen a lot of time people use the English definition of "Intrinsically Safe", and not meaning the NFPA 70 definition of "Intrinsically Safe". That should definitely be avoided, but something to look out for when discussing this type of stuff with people.
I've seen a lot of time people use the English definition of "Intrinsically Safe", and not meaning the NFPA 70 definition of "Intrinsically Safe". That should definitely be avoided, but something to look out for when discussing this type of stuff with people.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
You are aware that nonincendive wiring also requires a control drawing, right? [Section 501.10(B)(3)] Ever since our colleagues at ISA became the US's representative to the IEC HAZLOC Committees, they have attempted to mangle hazardous locations a fair amount. Effectively, with the various NEC Informational Note (IN) references to ANSI/ISA-12.12.01-xxxx, Nonincendive Electrical Equipment for Use in Class I and II, Division 2, and Class III, Divisions I and 2 Hazardous (Classified) Locations, nonincendive isn't much more forgiving than IS.
My mistake in calling in confusing nonincendive with sections in 501 that allow for certain "Instruments" to use general purpose enclosures. I did not actually mean to refer to the protection method of nonincendive circuits, but I meant the allowance to use general purpose enclosures.
For example, in a Class I Div 2 location, if I have an air solenoid valve bank that is driven via ethernet, I believe that section 501.105 of the 2017 NFPA 70 is saying that I can am permitted to use this instrument in its normal general purpose enclosure, as long as I follow the wiring methods for Class I Div 2.
Is this correct? I am looking for the correct rationale to use standard general purpose equipment that that is not arcing or in any other way an ignition source for the Class I Div 2 location.
For example, in a Class I Div 2 location, if I have an air solenoid valve bank that is driven via ethernet, I believe that section 501.105 of the 2017 NFPA 70 is saying that I can am permitted to use this instrument in its normal general purpose enclosure, as long as I follow the wiring methods for Class I Div 2.
Is this correct? I am looking for the correct rationale to use standard general purpose equipment that that is not arcing or in any other way an ignition source for the Class I Div 2 location.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
That's correct; just don't confuse non - arcing, non-sparking, nor non-high temperature with nonincendive which is very narrowly defined. You should also review Section 500.8, especially Subsections 500.8(B), (C) and (D) thoroughly; but give the whole Section a good going over.
Thanks for the clarification. To use the ethernet driven solenoid valve bank example again, it does not have any arcing/sparking or other ignition sources. However, if it has a small fuse inside of it to protect the electronics, would this then make it unusable in a Class 1 Div 2 location? Most electronics are protected by internal/integral standard general purpose fuses, right? So that would make most electronic devices not usable in a Class I Div 2 location?
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