CWillcox
Member
- Location
- New Paris, OH
I have been asked to consider changing our site from using divisions to zones. Has anybody done this before? If so, what pitfalls did you find along the way? Lessons learned? Advice?
Area Classification Change from divisions to zones
- Thread starter CWillcox
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Zones do not transfer directly to divisions, but are reasonably close. NFPA has done so with arguably acceptable results. See NEC section 505 and 506 for zone definitions, and Section 516 where they have been implemented. There are some differences that can be confusing, especially if both systems remain in use. Zones allegedly result in lower installed costs and enhanced maintainability when zone rated electrical equipment is installed. The use of zones is apparently more common in Europe than in the US. I'm not sure there is much to be gained in converting from one system to the other at an existing facility.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
What little disagreement I have with squnsel on this is more semantic than substantive. It?s my opinion that the definitions of NEC Zones were ?force fit? into Division definitions and the only significant difference is Zone ?x0? (where ?x? is blank or ?2?) is definitely hazardous under any reasonable active process operating or maintenance condition. (Zone n1 ?may? be hazardous under ?normal? conditions ? but isn?t necessarily)
That being said, in NEC jurisdictions you only need to change the current area classification document?s legend from Division 2 to Zone x2 and Division 1 to Zone x1 then identify the interior of tanks and such as Zone x0 (where there probably isn?t any wiring anyway) and you?re done.
Well, not quite. Here is where the real problems start. The Groups and ?T-Classes? don?t match up nearly so well. See Section 500.8 (B) (1) for the significance. Note the requirement is for ??specific gas, vapor, dust, or fibers/flyings that will be present.? Then compare the ?Group? definitions in 500.6 to those in 505.6. For a complete education compare the ?T-Classes? of various materials per Divisions and Zones in NFPA 497 or 499.
The only significant benefit to NEC Zones is the ability to use the ?Increased Safety? (AEx e) protection technique in Zone 1. The other protection techniques permitted in Zone 1 are already effectively permitted in Division 1 or are generally unavailable commercially; e.g. AEx q.
From a manufacturers perspective, we cannot offer a building loaded with controls and HVAC any cheaper in Zone 2 vs Div. 2
However, reclassifying the building as Zone 1 inside (vs Div 1) is less expensive. One major benefit is junction boxes (with terminals only) do not need to be in Nema 7 (ex. proof) boxes, rather, increased safety Exe boxes can be used. Hazloc Lighting is another area that is "slowly" coming around to be cheaper in Zone 1 offering.
However, reclassifying the building as Zone 1 inside (vs Div 1) is less expensive. One major benefit is junction boxes (with terminals only) do not need to be in Nema 7 (ex. proof) boxes, rather, increased safety Exe boxes can be used. Hazloc Lighting is another area that is "slowly" coming around to be cheaper in Zone 1 offering.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I acknowledged the "AEx e" "benefit" in my own reply; however, sealing can become a nightmare, just trying to figure out when and where to place seals. Also note "EX e" is NOT NEC acceptable; it must be marked "AEx e"
weressl
Esteemed Member
So Bob, wht's going to happen with the Class/Div. listing of all the equipment in the area?
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Excellent question. A lot of equipment originally designed for US domestic Division applications are now marked with both schemes.
Section 505.9 (C)(1), permits Division listed equipment to be Zone marked automatically with a few restrictions. Note though, the "few restrictions" are very specific requirements in 505.9 (C)(1)(2)&(3) to match Zone Groups and Temperature Classes. As I said in my original response, they don't line up nearly as well. While dropping the alpha part of the T-code usually works, it isn't necessarily absolute for the ?? specific gas...that will be present? - and matching Groups can still be a real bear altogether.
CMP14 was able to force-fit Zones into Divisions only because most Panel members were ignorant of (and the ones that weren't ignorant deliberately ignored) the fundamentals of classic IEC Zone based electrical area classification. That's why they originally required a PE to do the area classification; but that offended the "User" Panel members that weren't PEs and has since been dropped.
In my opinion, reclassifiying Divisions to Zones is a very dangerous proposition; nevertheless, it can be done if one knows what they are doing. Trying to determine if existing equipment only marked for Division is suitable for a location reclassified to Zones is not a trivial exercise - no matter what the manufacturers' try to tell you.
weressl
Esteemed Member
Hey, we can take this routine on the road?
Seriously, how would one generate documentation of existing equipment suitability if it is only marked for Division, which is the large majority of existing plants? With instruments, since you're replacing them more frequently, you have a better chance that it will be dual labeled, but with electrical equipment it is a far less chance that you have dual label. Even if it HAS a dual label, it would not necessarily mean that the Zone'd label is suitable for the application.
My main concern comes form the practicality of the issue on the trades level. There are few and far between the electrician and instrument technician who truly understands AND can apply the EAC principles in installations for the Division applications. WHat poercentage of those would you guess have a working understanding of the Zone'd requirements?
I feel that the introduction of the Zone'd installation was unnecessary and that it weakens the overall safety of the Chemical industry.
This is what it comes down to from the plant perspective. I've had a few consulting engineers occasionally want to use a zone 2 product in our division-based plant and we've said no, it needs to marked in the division system so the less technical folks don't freak out if they read the nameplate. It is already difficult enough to teach electricians some of the sealoff requirements around different types of boxes and different equipment in the boxes, and why 600V cables don't need to be sealed at either end or at the boundary when transitioning from div 2 to non-classified if they meet UL 1277.
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