A customer has a requirement that we place a ?non-incendive? resistor of 200 Ohms in line with signals that go from the main control cabinet to the valve that we are supplying. The environment is Class I, Division 2 and the valve is CSA listed for Class I, Division 2, ABCD. If we put the resistor in line, the valve will not function because there is too much voltage drop. I've never seen this requirement before, but my initial reaction is that they don't need the resistor in this circuit because the valve is already non-incendive. Am I missing something?
Non-incendive Resistor in wiring
- Thread starter JeanH
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mivey
Senior Member
I don't recall having seen a fixed resistor that is incendive. I have seen plenty that were not intrinsically safe.
Don't see what the valve's incendive status has to do with the resistor.
I also don't understand why they would specify a resistor that would make the valve inoperative.
Don't see what the valve's incendive status has to do with the resistor.
I also don't understand why they would specify a resistor that would make the valve inoperative.
Perhaps a polyswitch would serve the purpose better.
http://www.circuitprotection.com/catalog/fundamentals/PSWFundamentals.pdf
mivey
Senior Member
What were they trying to do with the resistor?
Non-incendive Resistor in wiring
I have never seen this requirement before. However, I think they are trying to reduce the voltage going into the valve to a level that would be non-incendive. The valve electrical components are already non-incendive, so I don't think we need the resistor.
I am also wondering if there some other reason they are using the resistor.
I have never seen this requirement before. However, I think they are trying to reduce the voltage going into the valve to a level that would be non-incendive. The valve electrical components are already non-incendive, so I don't think we need the resistor.
I am also wondering if there some other reason they are using the resistor.
Cold Fusion
Senior Member
- Location
- way north
Just curious: Is this a 4 - 20ma loop they want the 200ohm resistor in-line?
This part is pure guess:
Sure that is why they want it. The valve components are non-incindive, but the 4 - 20ma loop supply to the valve is not.
But if the signal is a DI or DO, then this guess does not apply
None I know of.
Have you asked them? Might be worth while since their "I wants" don't work.
cf
mivey
Senior Member
Aha! That makes more sense. Maybe a mix-up of specs on the customer's part.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
This sounds like an attempt to make a nonincendive circuit, intrinsically safe; unfortunately, it isn't an NEC recognized method, never has been and is not ever likely to be.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I'm sure you do.
Do you have a manufacturer's control drawing that substantiates the nonincendive application for the resistor? [501.10(B)(3)]
toledo ron
New member
I have a client who would use a resistor in the contol panel to "current limit" 24vdc control circuits for non incendive disign. Is the idea of energy limiting a valid concept for non incendive circuits per the NEC? If so then what is a suitable method of achieving this?
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Yes, it is a valid concept - but only when applied as part of a control drawing. See the requirements in 501.10(B)(3) and the definitions in in 500.2.
tkirk
Member
- Location
- Denver, CO
How much current do you need to drive your valve, and at what voltage? I'm guessing something in the listing/certification documentation for the valve is requiring an energy limited power source, or else somebody is adding requirements to your design that don't need to be there. If you are being required to provide an energy limited power source to the valve you might not have a choice but to put in an active current limiting component or else a separate power supply that is listed for the area and current-limited, and then just control the power supply for the valve from your controller. Most passive energy limiting barriers simply won't pass enough current to drive a valve, because they are specified based on max current into a short circuit. We've run into this before (usually trying to put solenoid valves in Class 1 Div 1 areas), and its a sticky design problem. If the entire system is certified as a system by an NRTL with an appropriate control drawing, you can sometimes avoid the issue.
I'm definitely interested in how you solve this problem, since I've seen it come up before.
I'm definitely interested in how you solve this problem, since I've seen it come up before.
ControlDude2000
Member
Actually, ASCO calls for the 200 ohm resister at the left hand bottom of their NI solenoid data sheet.
http://www.ascovalve.com/Common/PDFFiles/Product/NIFW_ValvesR3.pdf
They have the same notation on their IS valve sheet as well.
http://www.ascovalve.com/Common/PDFFiles/Product/IS_ValvesR5.pdf
The NI data sheet references NI. Both data sheets have a 2 Deg C = 36 Deg F temperature rise. Must be gobal warming.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Technically, the solenoid is an inductive Simple Apparatus. [504.2]
I reviewed the data sheets and, when used in NI and IS applications, the solenoids still must have a barrier. In "Non-'IS' systems", and (I suspect a misprint in NIFW_ValvesR3.pdf) "Non-'NI' systems", in absence of a barrier across the terminals, the 200 ohm resistor simply limits the power (joules per second) from stored energy that the solenoid could deliver to the system. This in turn limits the Minimum Ignition Current (MIC) [500.2] which, since 1999, along with Maximum Experimental Safe Gap (MESG) are the primary defining qualities of Class I material Groups.
For ?non-?NI? system? applications, this is somewhat curious since a solenoid can be used in Division 2 in a ?general purpose? enclosure with or without a barrier or inserted resistor anyway.[501.105(B)(3)]
In any case, I still emphasize the need for a manufacturer?s control drawing which is an NEC requirement for either IS [504.10(A)] or NI [501.10.(B)(3)]applications.
ControlDude2000
Member
IS vs. NI
IS vs. NI
Back to a variation of my question under another topic:
These two solenoids have the same entity parameters and electrical characteristics. One is IS and one is NI.
I have a plant full of the IS solenoid connected to barriers and DCS I/O.
If I yank the barriers and install NI I/O (and un-identify the IS wiring, etc.), can I keep the IS solenoids or do you have to replace them with NI solenoids?
The control drawings with the IS solenoids do not show NI examples and the entity method assumes mating to an IS barrier or IS I/O.
IS vs. NI
Back to a variation of my question under another topic:
These two solenoids have the same entity parameters and electrical characteristics. One is IS and one is NI.
I have a plant full of the IS solenoid connected to barriers and DCS I/O.
If I yank the barriers and install NI I/O (and un-identify the IS wiring, etc.), can I keep the IS solenoids or do you have to replace them with NI solenoids?
The control drawings with the IS solenoids do not show NI examples and the entity method assumes mating to an IS barrier or IS I/O.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
My ?gut? response is that it should be acceptable; but if I had to substantiate it with a document reference, I couldn?t. I couldn?t base it on any coherent set of classified location installation principles either.
Part of the problem is the root documents for both ?IS? and ?NI? systems are ISA (Instrumentation, Systems, & Automation Society) rather than NFPA. ISA is dominated, though certainly not entirely controlled, by manufacturers. That?s why their seat on CMP 14 is listed as [M]anufacturer.
As I suggested before, contact FM directly for their opinion.
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