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October 2001

Using code changes to boost profits

by Paul S. Babiarz

Uniform designs and single sourcing offer opportunities for improvements, savings.

Practically all manufacturing facilities have hazardous areas that engineers must manage. The National Electric Code (NEC) and Canadian Electrical Code (CEC) have now changed to give those in North America choices on how to classify hazardous areas, what types of equipment can be installed, and how to wire future installations.

North American industries have historically classified hazardous areas as either Division 1 or 2, based on the NEC or CEC. Now, with the changes to both codes, engineers can classify hazardous areas containing gases and vapors (Class 1) as Zone 0, 1, or 2.

Division 2 is equivalent to Zone 2, while Division 1 is either Zone 0 or 1. Zone 0 designates areas that are continuously hazardous (e.g., inside a vented fuel tank); Zone 1 encompasses all other Division 1 areas.

Why change in North America?

North American industry has grown accustomed to the division classification system. Plants in the U.S. and Canada are safe and operating efficiently. So why change to a new classification system? The answer is, the business world continues to shrink, and most companies must now think globally.

Many industrial end users and manufacturers want a harmonized international standard so that a new plant built offshore would have the same equipment and installation standards as one built domestically. This allows them to take advantage of single-sourced materials and less expensive alternatives not always available elsewhere. The U.S. and Canada debated the merits of classifying hazardous areas as zones instead of divisions for more than 20 years. Because the International Electrotechnical Commission standard was unlikely to change, the 1996 NEC allowed zones, and Canada followed in 1998.

Despite this change to the electrical codes, most U.S. petrochemical plants have not changed their standards and still classify their hazardous areas according to the division system. They identify more than 90% of the areas as Division 2 instead of the more expensive Division 1. The oil patches of Western Canada and OEMs that build products for use around the globe have more readily accepted the zone concept.

The differences

The most obvious difference is that division-rated products are usually metallic and of American or Canadian origin. Zone-rated products, on the other hand, are usually associated with European designs employing more plastics. In reality, it is the form of protection used that is the major difference.

Terminations are the key to understanding the difference in the installation methods of zone- and division-rated equipment. “Increased safety” is a zone system classification that allows nonexplosionproof enclosures (normally nonmetallic housings) with approved wire terminations to be used in Zone 1, even though only metallic explosionproof enclosures are used for Division 1. Terminations must demonstrate that they do not heat up or vibrate loose, and that they have sizable creepage and clearance distances to prevent arcing, in order to earn the “increased safety” rating. The division system assumes all wire terminations are sources of ignition because they could vibrate loose or short out and create an arc.

This leads to major differences in product design. A push-button control rated for Division 1 has an explosionproof metallic housing. A push-button control rated for Zone 1 has a nonmetallic housing. Each contains an explosionproof contact block. The first has an explosionproof rating for Division 1, and the other has flameproof and increased safety ratings for Zone 1. Each contact block prevents arcs from switching operations from igniting gases within the control station. Why, then, must the contact block located in a Division 1 area be housed in an explosionproof enclosure when the Zone 1-rated control station is in a nonmetallic enclosure?

Division 1 areas consider the terminations to be ignition sources. If volatile gases and air accumulate inside an explosionproof enclosure and a spark from a wiring fault on the terminals then ignites them, the enclosure must contain the explosion. As the hot gases escape the enclosure by passing across a flat, threaded, or serrated joint, they cool and can no longer ignite gaseous mixtures in the hazardous area. In a division 1 area, the contact block must be inside an explosionproof enclosure rated for the area.

The zone concept does not consider wire terminations an ignition source if they have an “increased safety” rating. If the contact block is flameproof and has “increased safety” terminals, the switch housing may be nonmetallic with a suitable environmental protection rating to protect against moisture and dusts.

Will zones save money?

Determining which system is safer, less expensive, or easier to install is very difficult—somewhat like comparing the metric and U.S. systems of measurement. Each has its own merits. Usage depends on user preference, how the areas are classified, and the wiring systems used in the facility. However, some points are clear. Products to be used in Europe may not have twist-on connectors or wire nuts; designers must use terminal blocks or screw terminals. North America will not be quick to abandon twist-on connectors in favor of terminal blocks for branch circuits, however, when both systems are safe if properly installed.

North American users have done an excellent job of squeezing costs out of the supply chain. Further, they have the best of both worlds because the code allows the use of zone-rated equipment in the popular Division 2 locations. With only a few exceptions, there will not be significant cost differences between zone- and division-rated products.

Users can save big bucks immediately, however, with Zone 2 restricted breathing high-intensity discharge light fixtures (InTech, October 1999). Restricted breathing enables one to use higher-wattage fixtures, and thus fewer fixtures, in Division 2 locations. There are also nonmetallic distribution panel boards, control stations, and fluorescent lights with more options for emergency use and monitoring usage. One must weigh the installation costs of these products.

The installation cost usually depends on the wiring methods used. Though conduit wiring usage remains steady, there is a growing trend toward cable. In hazardous areas, this normally means some type of armored cable or a power limited tray cable for instrumentation or low-power circuits. Canada embraced TECK, a type of armored, PVC-jacketed cable, a decade ago in favor of conduit. There are initiatives in Western Canada to go one step further and abandon TECK in favor of a less expensive nonarmored cable for Zone 2 locations. This would reduce installation costs significantly.

With most areas classified as Division 2, North American users have the best of all worlds. They can use any Zone 0-, 1-, or 2-rated product, as well as any Division 1- or 2-rated product, in their hazardous areas. While it may be difficult to detect costs savings on materials, there is a wider selection of products to choose from. Thus, users can select from metal or plastic with cable or conduit entries to suit their environment. If the area is subject to corrosion, there are new corrosion-resistant enclosures available. If the location is subject to a high degree of mechanical abuse, then metallic products may offer lower ownership costs. IT