Nonincendive Wiring

[japott]

Does anyone know of a good reference on how to apply nonincendive wiring as a hazardous area protection techique? I have a copy of the ANSI standard (12.12.01-2000); however I find the standard very confusing. I have not been able to locate any useful technical information relating to nonincendive wiring on the internet.

 

[BradJ]

Good question. I'm struggling with this as well. The 2002 NEC has an added definition for Nonincendive Field Wiring and related code, but it's only added confusion to the issue. I can't say that my interpretation is valid as it's very unclear and poorly worded. I'm sure it makes perfect sense to the person/group that wrote it, but the wording sure leaves the door open to multiple interpretations.

The NEC... written by lawyers, for lawyers. Job security. If it were clear, they'd be out of job.

Oh, and the NEC Handbook (another $170) is worthless on this particular topic.

If you find a good resource, please post it.

 

[resqcapt19]

The NEC permits the use of nonincendive wiring using ordinary wiring methods in Class 1 Division 2 area. What this means is that the use of costly explosionproof devices is not required. The nonincendive wiring will still require seals at the area boundaries, but not at the devices.
As far as the NEC being written by lawyers, that is not true. The NEC is a consensus standard and is written by the users and volunteer code panel members.
Don

 

[BradJ]

I read the abstract for ANSI 12.12.01-2000. It appears to be details on designing components/equipment which will be certified for Class 1, Division 2. It doesn't say it covers installing these devices in a system.

As for the NEC, it sure reads like a legal document. I understand there's a panel involved, but I'd be shocked if there were lawyers on that panel.

Can somebody explain this to me?

"Nonincendive Field Wiring. Wiring that enters or leaves
an equipment enclosure and, under normal operating conditions
of the equipment, is not capable, due to arcing or
thermal effects, of igniting the flammable gas-air, vapor-
air, or dust-air mixture. Normal operation includes opening,
shorting, or grounding the field wiring."

That last sentence is the stumbling block. It sure sounds like a fault condition to me. Unless they are talking about a switch or other hazardous-are field device, but then they should have been more clear about it.

If you really want to strain your brain, try to decifer this. I had to read it about four times before I could even guess at it's meaning.

"Associated Nonincendive Field Wiring Apparatus. Apparatus
in which the circuits are not necessarily nonincendive
themselves but that affect the energy in nonincendive
field wiring circuits and are relied upon to maintain nonincendive
energy levels. Associated nonincendive
field wiring apparatus may be either of the following:
(1) Electrical apparatus that has an alternative type of protection
for use in the appropriate hazardous (classified)
location
(2) Electrical apparatus not so protected that shall not be
used in a hazardous (classified) location
FPN: Associated nonincendive field wiring apparatus has
designated associated nonincendive field wiring apparatus
connections for nonincendive field wiring apparatus and
may also have connections for other electrical apparatus."

Finally, I understand that the NEC is not intended to be a training document. If you are new to this, find someone who isn't. But much of the verbage that they have added to the 2002 code (vs the 1999 code) to "clarify" nonincendive installation seems to be intentionally vague, in my opinion.

-Brad

 

[BradJ]

japott,

One of my contacts told me to get a hold of FM document #3611, which is supposed to cover Nonincendive installations. You can see a complete list of FM docs at:

http://www.fmglobal.com/research_standard_testing/product_certification/approval_standards.html

There's an 800 (877 actually) number at the bottom you can call to order the docs (printed format only), but they are free! Hard to believe after dealing with NFPA, ISA, IEEE, IEC, etc. I just ordered some of the documents and they said they should arrive in two weeks or so.

Hope this helps,
-Brad

 

[19182]

Gersan electric, it is a istanbul based manufacturer of cable trays, earthin items and such...
The striking point is their "corrosion resistant products" which do rust in a short time right after the installation of their products. Following the assembly, almost 1 year after, their cable trays, joints and most of the connector parts including the bolts turned out to get rusting. As an electrical engineer I visited the construction site and I observed the corrosion incidence. It no doubtly will get worse and deeper. I wish the best of luck to those companies working with them, to those who trust gersan products. I can simply admit; "the worst products I have ever seen in my life as an engineer."
Please keep in mind that I am an engineer since 1981.
Just wanted to share my experience.
Thanks
Berk Elbistan

 

[RAMConsult]

Simply put 'nonincendive' is different than 'intrinsically safe' on two points- 1. energy available for ignition under normal versus fault conditions, and 2.) nonincendive is only allowed in Division 2 and Zone 2 installations. Check out this article

http://www.ul.com/regulators/is_circuits.pdf

It explains in plain language the differences between 'Intrinscially Safe' and 'Nonincendive' very well.

 

[BradJ]

RAMConsult,

Thanks for the additional doc, it does an excellent job of describing Intrinsically Safe installations. While it does mention Nonincendive installations, it still does not discuss how to design a proper Nonincendive installation. It references other documents (Vendor Control Drawings, NEC, ANSI/ISA RP 12.6-1995), but these documents don't provide a good description either.

I have had no luck getting control drawings from any of the Nonincendive equipment vendors we are looking at using. The closest I came was on a Div 2 PC from Daisy Data. I was told by another source they were required for the Nonincendive rating, but each of the manufacturers I spoke with said they are not. The vendors were very helpful describing how to install their equipment over the phone, but none of them had it in writing, which is the only acceptable means of documentation allowed in the circles which I work. It seems like no one really wants to commit to anything on this subject.

I'm still hoping FM#3611 will shed some light on this.

-Brad

 

[RAMConsult]

Brad, You may be digging deeper than necessary. In the document you'll notice that the two terms are used interchangeably, the only difference is the Division and/or Zone that the equipment is allowed in. The design philosophy leading to the development and commercialization of Intrinsically Safe and Nonincendive equipment/wiring systems was to ease up on the requirement of using expensive and labor intensive wiring methods such as RMT, purged enclosures, sealing boxes, etc. It is now possible to use ordinary unclassified wiring methods between devices specifically approved and visibly marked for this purpose. Physical protection is another issue, the main requirement for this type of wiring is that it be kept at least two inches from 'regular' wiring, be in a shielded trough when in close proximity to 'regular' wiring, or be of a different color than any other conductors in the system. I don't understand why your vendors are not more forthcoming with their info, perhaps it's the over-litagous society in which we live.

 

[BradJ]

I suspect I am. The problem is, there appears to be sufficient rope in the NEC to hang myself and the others involved in approving this design, should an accident ever occur. Lawyers just love vague descriptions that they can warp to their liking. That's why we need printed literature.

The entire team knows that what we have planned is safe, but proving it in a court of law is another story. Corporate America is no longer backing their engineering groups, I've actually known some engineers that have been officially notified (had to sign & return the notification) by their own company's legal department that they are personally liable for their designs.

Unless there is an official NEC, UL, FM or Control Drawing document that says "this is it, this is all you have to do to meet code", we may end up not installing this equipment because no one will stick their neck out.

Interesting you mentioned separation of wiring and different wire color, because I could not find any mention of that in NEC (and I did a search on the entire 718 pages). It's quite clear for I.S (504.80). It does mention separate cables, or wires of sufficient insulation thickness, but that's it. The UL document you sited was pretty vague on what was a requirement of I.S. vs Nonincendive.

The search continues.....

 

[wired1]

BradJ

To your previous question what NEC calls a device that produces an arc in normal operation, is precisely as you have surmised, a switch. Sounds like lawyer-speak, but think about it - pushbuttons, relays, dc motors with their commutators, all fall into this category.

 

[busbar]

BradJ, the 'rope' is in Chapter 5 of the NEC, but harder to recognize because in this case, it's more like piano wire.

 

[japott]

I am amused that, after 15 months of no replies there is suddenly great interest in this topic! After some additional research I believe I can help clarify the nonincendive wiring issue.

Simply put, nonincendive wiring is "intrinsically safe" wiring without the barriers/isolators (besides that the two wiring methods are quite similar). The key to this is the requirement that nonincendive wiring be evaluated under normal operating conditions only, whereas intrinsically safe wiring has additional protection against fault conditions. The word "fault" in this context is not intended to mean a short circuit in the field wiring but rather an abnormal operating condition where the energy available to the circuit is increased beyond design levels. Such may be the case during a power surge, for example. The intrinsically safe barriers are designed to prevent the abnormally-increased energy levels from entering the hazardous location, which is why intrinsically safe wiring is allowed in Div 1 areas.

The ANSI standard (12.12.01-2000) does in fact contain the requirements for the field wiring, although one has to spend a signigicant amount of time with the standard in order to digest the information. Another resource that I found helpful: "Electrical Installations in Hazardous Locations" by Peter J. Schram and Mark W. Earley

As to why there is so little information on this topic, I surmise that has laregely to do with the marketing efforts of the intrinsically-safe industry. In an effort to sell their products, they have invested a great deal of effort increasing public awareness of the intrinsically safe (IS)wiring method. IS wiring is also safe under all conditions, which appels to our conservative nature as engineers. Nonincendive wiring, by contrast, requires no additional equipment in the circuit and has no industry champion promoting its use, and is only applicable in limited circumstances (Div 2 areas).