Explosion-Proof Motors And Applications Hazardous Location

Reliance has one of the broadest and most complete XP motor product lines offered by the industry. What ever your customers needs are for XP motors, Reliance will be able to better supply your customer with more motors for more applications, backed by many years of XP motor experience and research, than any other motor manufacturer. Now, a word of caution. Explosion-Proof motor applications are very serious business. The misapplication of an XP motor can result in substantial problems for the motor user. For this reason, no Sales Engineer should suggest what XP motor specifications are needed by the customer for a particular application. It is the responsibility of the customer and the local governing authority to determine what type of hazardous location is present and what motor specifications are necessary. Ask that your customer supply you with the Class, Group and "T" Code requirements for all hazardous location motor applications. Class and Group specifications are always required to place an order for an XP motor and "T" codes are nice to have also. "T" codes are required, however, for "Class I Group D only" XP motor orders. Do not make any assumptions relative to the customers requirements. For more information concerning XP motor requirements and applications refer to the National Electric Code (NEC), or the NFPA manual which covers the fire hazard properties of flammable liquids, gases and volatile solids. These two documents and many other informative documents relating to hazardous materials and installations can be purchased from the National Fire Protection Association.

Class and Groups available

1. Class l, Group D, Class II Groups F & G
   (Standard multilabel motor found in Price and Stockbooks.)
2. Class II, Group E.
3. Class l, Group C
   (Available on 48 and 56 frame, TENV only).
   Insulation: Class B or F available on all except Class I Group D which must be Class B insulation.

1. Class I Group D, Class II Groups F & G
   (Standard multilabel motor found in Price and Stock books.)
2. Class l, Group C.
3. Class II, Group E.
4. Class l, Group D only
   (Found in Price and Stock books)

In 1974, Underwriters, Laboratories made revisions to the requirements for explosion-proof motors. The effect of the new standards were to increase the assurance that XP motors would not exceed specific U/L defined surface temperatures. The new U/L standards, effective for motors manufactured after March 7, 1975, had three results:

1. New maximum motor surface temperatures have been specified for all classes and groups of atmosphere.
2. Temperature limiting devices within the motor enclosure are required in motors which may exceed the specified maximum safe surface temperature.
3. All explosion-proof motors must be marked to indicate the maximum motor surface temperature.

In response to these revisions, Reliance has made construction and control circuitry changes to its explosion-proof product line. The addition of temperature limiting devices has been as follows:

In certain applications with 1 hp and below motors, the standard automatic reset thermal overload may not be satisfactory; for example, where there is danger to driven machinery or personnel who may be investigating the motor shut-down. Where this condition exists, manual reset overload devices or thermostats may be required. It is the users responsibility to notify Reliance where an automatic reset device is not suitable for his equipment, however, the sales engineer should review the customers applications for acceptability of this feature. Manual reset thermals can be supplied on a production basis where necessary.

All 140T frames and larger AC motors incorporate thermostat temperature limiting devices. These thermostats are to be used in conjunction with the users control circuits in order to achieve the surface temperature limitation which is required by UL..

The third result, as mentioned above, of the new U/ L requirements for explosion-proof motors is that all XP motors must be marked to indicate the maximum operating surface temperature. A "T" Code is used as the Temperature identification value and it is taken from the National Electric Code. The "T" Code is based on the minimum ignition temperature of the substances to be found in the hazardous location. (Ignition temperature is when substance will start to burn or explode,) The code, when marked on a motor nameplate, represents the highest temperature that could be obtained on the motor surface under any normal or abnormal operating conditions including locked rotor, single phasing or overloading, and is chosen to be below the ignition temperature of the substance in the hazardous area. The "T" Code designations apply to motors and other types of electrical equipment subject to hazardous location classification.

For reference, the following is the complete temperature identification code table taken from the National Electric Code showing the U/L requirements for each class and group for which we label. Since the standard multilabel motor (Class l, Group D, Class II, Group F and G) meets T3B, this product also meets all the surface temperature codes higher than this, i.e., T1 through T3B.

Our policy on nameplate stamping of the NEC temperature codes is the following on frames 48-449T:

For special requirements not covered by these codes, contact AC Products for availability.

Reliance offers two standard XP motors in the Price Book and Stock Book: 1) standard multilabel XP motor for Class l, Group D and Class II, Groups F and G; and 2) limited application XP motor for Class l, Group D only (280°C and above-T2A). Since our standard multilabel motor is for more than one class and group, it carries a T3C (160°C) N/P operating code which reflects the lowest temperature for all the classes and groups listed for this motor.

Class I, Group D Only, XP Motor

Please note that this line of Class l, Group D only motors is limited exclusively to atmospheres with ignition temperature of 280° and above (NEC temperature code T2A). These are Class B insulated, 1.0 service factor for use in a 40°C maximum ambient only. Class B. 1.15 service factor is available by overframing. No Class F temperatures are permitted on these motors.

Since U/L requires that all Class l, Group D explosion-proof motors which have surface temperatures which may exceed 215°C (under all operating conditions) be specially marked, the 280°C Class l, Group D only motors will carry the U/L cautionary label which warns against installation of these motors in atmospheres with ignition temperatures less than 280°C. This cautionary label states:

"CAUTION: TO PREVENT IGNITION OF HAZARDOUS ATMOSPHERES, THIS MOTOR SHOULD NOT BE INSTALLED IN AN AREA WHERE VAPORS OR GASES HAVING AN IGNITION TEMPERATURE LESS THAN 280°C (OR 536°F) ARE PRESENT."

As the application of the Class l, Group D only motor is for 280°C ignition temperatures and above, sales engineers must solicit customers for definition of the maximum motor surface temperature requirement in terms of the appropriate NEC temperature code listed.

This code is to be specified by the customer on the purchase order and likewise must be specified on the sales order as CL1 , Grp D, T2A (or 280°C) so that the correct product can be supplied. If a temperature code is not specified on a CL1 , Grp D only order, the motor will be supplied with thermostats and priced accordingly.

Introduction

Class is the term used to provide a general definition of the physical characteristics of the hazardous material in the area of the motor application.

Group is a term used to selectively combine into groups the explosive properties of materials. Groups are listed from A through G with Group A requirements being the most stringent from a motor design point of view and B. C, etc. being progressively less stringent.

Division is a term used to describe the possibility of hazardous materials being present at a particular location. There are two divisions listed. Division (1) includes potentially explosive atmospheres or conditions which are or could be present continuously. Division (2) includes potentially explosive atmospheres that normally would not be present but could be present in the event of equipment failure, a spill or other malfunction.

Motors which are acceptable for a Division (1 ) location are also suitable for Division (2) location, however, the converse is not true.

NEC ARTICLE 500 - HAZARDOUS
(CLASSIFIED) LOCATIONS

(a) Approval for Class and Properties. Equipment shall be approved not only for the class of location but also for the explosion properties of the specific gas, vapor, dust, fiber or flyings that will be present. In addition, equipment shall not have exposed any surface that operates at a temperature in excess of the ignition temperature of the specific gas, vapor, dust, fiber or flyings.

The characteristics of various atmospheric mixtures of hazardous gases, vapors, and dusts depend on the specific hazardous material involved.

(b) Marking. Approved equipment shall be marked to show the Class, Group, and operating temperature, or temperature range referenced to a 40°C ambient, for which it is approved.

The temperature range, if provided, shall be indicated as identification numbers, as shown in Table 500-2(b).

Identification numbers marked on equipment nameplates shall be in accordance with Table 5002(b).

500-4, Class I Locations. Class l locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class l locations shall include those specified in (a) and (b) below.

(a) Class I, Division 1. A Class l, Division 1 location is a location: (1) in which ignitible concentrations of flammable gases or vapors exist under normal operating conditions; or (2) in which ignitible concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or (3) in which breakdown or faulty operation of equipment or processes might release ignitible concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.

This classification usually includes locations where volatile flammable liquids or liquefied flammable gases are transferred from one container to another; interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used; locations containing open tanks or vats of volatile flammable liquids; drying rooms or compartments for the evaporation of flammable solvents; locations containing fat and oil extraction equipment using volatile flammable solvents; portions of cleaning and dyeing plants where hazardous liquids are used; gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape; inadequately ventilated pump rooms for flammable gas or for volatile flammable liquids; the interiors of refrigerators and freezers in which volatile flammable materials are stored in open, lightly stoppered, or easily ruptured containers; and all other locations where ignitible concentrations of flammable vapors or gases are likely to occur in the course of normal operations.

(b) Class I, Division 2. A Class l, Division 2 location is a location: (1) in which volatile flammable liquids or flammable gases are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems, or in case of abnormal operation of equipment; or (2) in which ignitible concentrations of gases or vapors are normally prevented by positive mechanical ventilation, but which might become hazardous through failure or abnormal operation of the ventilating equipment; or (3) that is adjacent to a Class I, Division 1 location, and to which ignitible concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.

This classification usually includes locations where volatile flammable liquids or flammable gases or vapors are used, but which, in the judgment of the authority having jurisdiction, would become hazardous only in case of an accident or of some unusual operating condition. The quantity of hazardous material that might escape in case of accident, the adequacy of ventilating equipment, the total area involved, and the record of the industry or business with respect to explosions or fires are all factors that merit consideration in determining the classification and extent of each location.

Piping without valves, checks, meters, and similar devices would not ordinarily introduce a hazardous condition even though used for hazardous liquids or gases. Locations used for the storage of hazardous liquids or of liquefied or compressed gases in sealed containers would not normally be considered hazardous conditions also.

500-5. Class II Locations. Class II locations are those that are hazardous because of the presence of combustible dust. Class II locations shall include those specified in (a) and (b) below.

(a) Class II, Division 1. A Class II, Division 1 location is a location: (1) in which combustible dust is in the air under normal operating conditions, in quantities sufficient to produce explosive or ignitable mixtures; or (2) where mechanical failure or abnormal operation of machinery or equipment might cause such explosive or ignitible mixtures to be produced, and might also provide a source of ignition through simultaneous failure of electric equipment, operation of protection devices, or from other causes; or (3) in which combustible dusts of an electrically conductive nature may be present.

This classification usually includes the working areas of grain handling and storage plants; rooms containing grinders or pulverizers, cleaners, graders, scalpers, open conveyors or spouts, open bins or hoppers, mixers or blenders, automatic or hopper scales, packing machinery, elevator heads and boots, stock distributors, dust and stock collectors (except all-metal collectors vented to the outside), and all similar dust-producing machinery and equipment in grain-processing plants, starch plants. sugar-pulverizing plants, malting plants, hay-grinding plants, and other occupancies of similar nature; coal pulverizing plants (except where the pulverizing equipment is essentially dust-tight); all working areas where metal dusts and powders are produced, processed, handled, packed, or stored (except in tight containers); and all other similar locations where combustible dust may, under normal operating conditions, be present in the air in quantities sufficient to produce explosive or ignitible mixtures.

Combustible dusts which are electrically nonconductive include dusts produced in the handling and processing of grain and grain products, pulverized sugar and cocoa, dried egg and milk powders, pulverized spices, starch and pastes, potato and wood flour, oil meal from beans and seed, dried hay, and other organic materials which may produce combustible dusts when processed or handled. Electrically conductive dusts are dusts with a resistivity less than 105 ohm-centimeter. Dusts containing magnesium or aluminum are particularly hazardous and the use of extreme precaution will be necessary to avoid ignition and explosion.

(b) Class II, Division 2. A Class ll, Division 2 location is a location in which combustible dust will not normally be in suspension in the air in quantities sufficient to produce explosive or ignitible mixtures and where (1 ) dust accumulations are normally insufficient to interfere with the normal operation of electrical equipment or other apparatus or (2) dust may be in suspension in the air as a result of infrequent malfunctioning or handling or processing equipment, and dust accumulations resulting therefrom may be ignitible by abnormal operation or failure of electrical equipment or other apparatus.

Locations where dangerous concentrations of suspended dust would not be likely, but where dust accumulations might form on, or in the vicinity of electric equipment, would include rooms and areas containing only closed spouting and conveyors, closed bins or hoppers, or machines and equipment from which appreciable quantities of dust would escape only under abnormal operating conditions; rooms or. areas adjacent to a Class II, Division 1 location as described in (a) above, and into which explosive or ignitible concentrations of suspended dust might be communicated only under abnormal operating concentrations of suspended dust might be communicated only under abnormal operating conditions; rooms or areas where the formation of explosive or ignitible concentrations of suspended dust is prevented buy the operation of effective dust control equipment; warehouses and shipping rooms where dust-producing materials are stored or handled only in bags or containers; and other similar locations.

500-6. Class III Locations. Class Ill locations are those that are hazardous because of the presence of easily ignitible fibers or flyings, but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitible mixtures. Class Ill locations shall include those specified in (a) and (b) below.

(a) Class III, Division 1. A Class III, Division 1 location is a location in which easily ignitible fibers or materials producing combustible flyings are handled, manufactured, or used.

Such locations usually include some parts of rayon, cotton, and other textile mills; combustible fiber manufacturing and processing plants; cotton gins and cotton-seed mills; flax-processing plants; clothing manufacturing plants; saw mills and other woodworking locations; and establishments and industries involving similar hazardous processes or conditions.

Easily ignitible fibers and flyings include rayon, cotton (including cotton linters and cotton waste), sisal or henequen, istle, jute, hemp, tow, cocoa fiber, oakum, baled waste kapok, Spanish moss, excelsior, sawdust, wood chips and other materials of similar nature.

(b) Class III, Division 2. A Class III , Division 2 location is a location in which easily ignitible fibers are stored or handled.

Exception: In process or manufacture.

"GROUP" DISTINCTION

NOTE: This section is only meant to be informative. Do not try to select Group requirements for a motor application at any time and certainly not from this list. This list is not complete.

Group E: Atmospheres containing metal dust, including aluminum, magnesium, and their commercial alloys, and other metals of similarly hazardous characteristics having resistivity of 105 ohm-centimeter or less.

Group G: Atmospheres containing flour, starch, or grain dust or combustible plastic or chemical dust having resistivity greater than 105 ohm-centimeter.

• Petroleum refineries, and gasoline storage and dispensing areas.
• Industrial firms that use flammable liquids in dip tanks for parts cleaning or other operations.
• Petrochemical companies that manufacture chemicals from gas and oil.
• Dry cleaning plants where vapors from cleaning fluids can be present.
• Companies that have spraying areas where they coat products with paint or plastics.
• Aircraft hangars and fuel servicing areas.
• Utility gas plants and operations involving storage and handling of liquefied petroleum gas or natural gas.

• Grain elevators, flour and feed mills.
• Plants that manufacture, use or store magnesium or aluminum powders.
• Plants that have chemical or metallurgical processes . . . producers of plastics, medicines and fireworks, etc.
• Producers of starch or candies.
• Spice-grinding plants, sugar plants and cocoa plants.
• Coal preparation plants and other carbon-handling or processing areas.

• Textile mills, cotton gins, cotton seed mills and flax processing plants.
• Any plant that shapes, pulverizes or cuts wood and creates sawdust or flyings. Note: fibers and flyings are not likely to be suspended in the air, but can collect around machinery or on lighting fixtures and where heat, a spark or hot metal can ignite them.

In the days before the development and commercial introduction of explosion-proof, dust-ignition-proof, and intrinsically safe electrical equipment for use in hazardous locations, inspections authorities and insurance underwriters restricted the use of electric motors and other equipment having arcing or sparking contacts. Safety considerations prohibited the use of such equipment in hazardous areas, and the laws of many states required the segregation of electrical apparatus in nonhazardous locations.

The demand for electrical equipment suitable for use in hazardous locations increased rapidly with the growing use of electric power and with the introduction of manufacturing processes that released flammable gases and vapors, or combustible dusts, into the air. The early 1920's marked the beginning of a period during which the manufacturers expended much time and effort in the development of electrical equipment that would satisfy the exacting requirement of safety and, at the same time, be practical and efficient at a reasonable cost to the user. At the present time practically a complete line of this type of equipment is available for installation where required.

Concurrent with the development of equipment for safe use in hazardous areas, it was of increasing importance to define "hazardous locations" more clearly. This function is fulfilled by the National Electrical Code (NFPA No. 70, ANSI-C1). Article 500 defines and classifies hazardous locations in order that the inspection authorities enforcing the Code may judge as to the need for special equipment suitable for hazardous locations in any given area. It also serves as a basis for the classification and test of electrical equipment for hazardous locations by Underwriters, Laboratories, Inc.

Apparatus enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor which may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and which operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.

Explosion-proof equipment for use in the presence of combustible gases and vapors is required to be so constructed that gas- or vapor-air explosions occurring within the apparatus will not ignite surrounding gas- or vapor-air mixtures. In other words, the enclosures of the devices are required to withstand, with a factor of safety, specified gas- or vapor-air explosions without bursting or loosening of joints, and the joints are required to be of the metal-to-metal or metal-to-glass type with adequate widths and close clearances to arrest the propagation of flame from the interior of the enclosure to the surrounding atmosphere. Obviously, the devices are required to operate under full load and likely overload conditions without developing exterior temperatures above the ignition temperature of the flammable gas or vapor in which they are intended to be used.

Figure 1 - Explosion-proof and dust-ignition-proof motor cross-section (fan cooled) showing construction.

It will be noted that the explosion-proof form of construction just described is not vapor-tight. It is recognized that under certain conditions gas- or vapor air mixtures will enter the enclosure. Actual tests have shown that it is practically impossible to prevent entrance of gases or vapors, even during minor normal changes in temperature. Gaskets cannot be depended upon to exclude the flammable and explosive mixtures. Hence, the term "vapor-proof" is misleading when used wits reference to motors, lighting fixtures, and other equipment intended for use in Class I hazardous locations.

Figure 1 shows a cross-section view of a fan-cooled explosion-proof and dust-ignition-proof motor. Maximum clearance and minimum widths of joints at A and B are closely controlled to confine internal explosions in Class I motors and/or to exclude dust entrance in Class II motors. Similar controls are applied to joints between the conduit box and the motor frame, and between the conduit box cover and the conduit box base.

The inner shaft path dimensions at C are maintained to confine internal explosions on Class I motors. The outer shaft path dimensions at D are maintained to exclude dust from entering the motor chambers that house the bearings on Class II motors.

Figure 2 illustrates typical metal-to-metal joints as used in explosion-proof housings. The section "G-K,, shows the effect produced by internal explosions on flat joints.

Figure 2 - Explosion-proof joints are of the rabbet and flat type (used in motor of Fig. 1). Carefully machined surfaces and heavily bolted assemblies are effective in arresting flame from internal explosions.

Hazardous Locations Comparison

Temperature Classification Comparison

IEC Method Of Protection For Hazardous Location

Last Updated September 1, 1998