NEMA及IEC標(biāo)準(zhǔn)下的電機(jī)銘牌識(shí)別（連載四）

# 15：功率因數(shù) (PF)

銘牌上的功率因數(shù)有時(shí)縮寫為 PF 或 P.F。功率因數(shù)是有功功率 (W) 與視在功率 (VA) 之比，以百分比表示。功率因數(shù)也等于電流與電壓之間滯后角的余弦值 (“Cos”)。

對于感應(yīng)電機(jī)，功率因數(shù)會(huì)隨負(fù)載而變化?？蛰d時(shí)功率因數(shù)最小，隨著電機(jī)負(fù)載的增加而增加。功率因數(shù)通常在電機(jī)滿載或接近滿載時(shí)達(dá)到峰值。

它的值范圍為0到1，表示滿載狀態(tài)。功率因數(shù)最好接近 1 (100%)?？梢酝ㄟ^添加電容器來提高功率因數(shù)。

在 NEMA 電機(jī)中，功率因數(shù)縮寫為“PF”，在 IEC 電機(jī)中，功率因數(shù)標(biāo)記為“Cos”。

# 15: POWER FACTOR (PF)

Power factor on the nameplate is sometimes abbreviated as PF or P.F. Power factor is the ratio of active power (W) to apparent power (VA), expressed as a percentage. The power factor is also equal to the cosine (“Cos”) of the angle formed by the lag between the current with respect to the voltage.

For induction motors, the power factor varies with load. Power factor is minimum at no load and increases as additional load is applied to the motor. Power factor usually reaches a peak at or near full load on the motor.

It can vary from 0 to 1 and is for the full load condition. It is desirable to have high power factors close to unity (100%). The power factor can be improved by adding capacitors.

In NEMA motors the power factor is abbreviated as “PF” and for IEC motors the power factor is tagged as “Cos”.

# 16：服務(wù)系數(shù) (SF)

電機(jī)服務(wù)系數(shù) (SF) 是指電機(jī)在正確的電壓容差范圍內(nèi)正常運(yùn)行時(shí)，短時(shí)間內(nèi)能夠承受的過載百分比。它非常實(shí)用，因?yàn)樗梢栽诠浪愎β市枨蠛蛯?shí)際運(yùn)行功率要求時(shí)提供一些“參考”。它還能降低額定負(fù)載下的繞組溫度，防止間歇性溫升，并有助于抵消低電壓或不平衡的線路電壓。例如，開放式防滴 (ODP) 電機(jī)的標(biāo)準(zhǔn)服務(wù)系數(shù)為1.15。這意味著，一臺(tái)10馬力、服務(wù)系數(shù)為1.15 的電機(jī)，在短期使用時(shí)可以提供11.5馬力的功率。一些小功率電機(jī)的服務(wù)系數(shù)更高，例如1.25、1.35 甚至1.50。

NEMA 將服務(wù)系數(shù)定義為一個(gè)乘數(shù)，當(dāng)它應(yīng)用于額定馬力時(shí)，表示在額定電壓和頻率下，在服務(wù)系數(shù)規(guī)定的條件下可以承載的允許馬力負(fù)載。該服務(wù)系數(shù)可用于以下用途：

1. 彌補(bǔ)預(yù)測間歇性系統(tǒng)馬力需求的不準(zhǔn)確性。

2. 通過降低額定負(fù)載下的繞組溫度來延長絕緣壽命。

3. 處理間歇性或偶爾的過載。

4. 允許環(huán)境溫度偶爾高于40°C。

5. 補(bǔ)償?shù)碗妷夯虿黄胶怆娫措妷骸?/p>

然而，NEMA 在討論服務(wù)系數(shù)時(shí)也增加了一些注意事項(xiàng)：

1. 長時(shí)間以服務(wù)系數(shù)負(fù)載運(yùn)行通常會(huì)降低電機(jī)轉(zhuǎn)速、壽命和效率。

2. 電機(jī)可能無法提供足夠的啟動(dòng)和拉出扭矩，并且啟動(dòng)器/過載尺寸可能不正確。這反過來會(huì)影響電機(jī)的整體壽命。

3. 切勿依賴服務(wù)系數(shù)來持續(xù)承載負(fù)載。

4. 服務(wù)系數(shù)是在額定電壓、頻率、環(huán)境溫度和海平面條件下運(yùn)行而確定的。

大多數(shù)電機(jī)的開式電機(jī)占空比為1.15，全封閉式電機(jī)占空比為1.0。傳統(tǒng)上，全封閉風(fēng)冷 (TEFC) 電機(jī)的服務(wù)系數(shù)為1.0，但現(xiàn)在大多數(shù)制造商提供的TEFC 電機(jī)的服務(wù)系數(shù)為1.15，與ODP 電機(jī)相同。大多數(shù)危險(xiǎn)場所電機(jī)的服務(wù)系數(shù)為1.0，但某些用于 I 類應(yīng)用的專用電機(jī)的服務(wù)系數(shù)為1.15。

只有當(dāng)服務(wù)系數(shù)高于1.0時(shí)，才需要在銘牌上注明。

# 16: SERVICE FACTOR (SF)

Motor Service Factor (SF) is the percentage of overloading the motor can handle for short periods when operating normally within the correct voltage tolerances. This is practical as it gives you some 'fudge' in estimating horsepower needs and actual running horsepower requirements. It also allows for cooler winding temperatures at rated load, protects against intermittent heat rises, and helps to offset low or unbalanced line voltages. For example, the standard SF for open drip-proof (ODP) motors is 1.15. This means that a 10-hp motor with a 1.15 SF could provide 11.5 hp when required for short-term use. Some fractional horsepower motors have higher service factors, such as 1.25, 1.35, and even 1.50.

NEMA defines service factor as a multiplier, when applied to the rated horsepower, indicates a permissible horsepower loading, which may be carried under the conditions specified for the service factor at rated voltage and frequency. This service factor can be used for the following:

1. To accommodate inaccuracy in predicting intermittent system horsepower needs.

2. To lengthen insulation life by lowering the winding temperature at rated load.

3. To handle intermittent or occasional overloads.

4. To allow occasionally for ambient above 40°C.

5. To compensate for low or unbalanced supply voltages.

NEMA does add some cautions, however, when discussing the service factor:

1. Operation at service factor load for extended periods will usually reduce the motor speed, life and efficiency.

2. Motors may not provide adequate starting and pull-out torques, and incorrect starter/overload sizing is possible. This in turn affects the overall life span of the motor.

3. Do not rely on the service factor capability to carry the load on a continuous basis.

4. The service factor was established for operation at rated voltage, frequency, ambient and sea level conditions.

Most motors have a duty factor of 1.15 for open motors and 1.0 for totally closed motors. Traditionally, totally enclosed fan cooled (TEFC) motors had an SF of 1.0, but most manufacturers now offer TEFC motors with service factors of 1.15, the same as on ODP motors. Most hazardous location motors are made with an SF of 1.0, but some specialized units are available for Class I applications with a service factor of 1.15.

The service factor is required to appear on the nameplate only if it is higher than 1.0.

# 17：滿載標(biāo)稱效率

效率定義為輸出功率與輸入功率之比。電機(jī)損耗以熱量的形式存在，包括定子繞組損耗、轉(zhuǎn)子損耗、鐵芯損耗（磁滯和渦流）、摩擦和風(fēng)阻以及雜散負(fù)載損耗。

NEMA標(biāo)準(zhǔn)MG1-12.54.2提供了確定效率值的說明。該標(biāo)準(zhǔn)規(guī)定，銘牌上顯示的標(biāo)稱效率不得高于相同設(shè)計(jì)的大量電機(jī)的平均效率。此外，在額定電壓和頻率下運(yùn)行時(shí)，滿載效率不得低于與標(biāo)稱效率相關(guān)的最小值。

在比較不同電機(jī)制造商的效率時(shí)應(yīng)謹(jǐn)慎。由于整個(gè)行業(yè)沒有統(tǒng)一的標(biāo)準(zhǔn)方法，因此很難基于已發(fā)布、引用或測試數(shù)據(jù)來比較效率。最常參考的標(biāo)準(zhǔn)是IEEE 112（美國）、IEC（國際）、JEC-27（日本）、BS-269（英國）和 ANSI C50.20（與 IEEE 112 相同）。IEEE 112 在美國的應(yīng)用最為廣泛，同時(shí)允許使用多種測試方法。首選的測試程序是IEEE方法B，即電機(jī)滿載運(yùn)行，并直接測量功率。

通常，大型電機(jī)的效率高于小型電機(jī)。如今，高效三相電機(jī)的效率范圍從1馬力時(shí)的86.5%到300馬力時(shí)的95.8%。銘牌上顯示的效率值是“標(biāo)稱滿載效率”，該效率值是使用高精度測功機(jī)按照 IEEE 標(biāo)準(zhǔn) 112 方法 B 中規(guī)定的程序測定的。標(biāo)稱效率是指對大量相同電機(jī)進(jìn)行測試并確定該批次電機(jī)平均值后所得的平均值。有些電機(jī)的效率值可能更高，有些電機(jī)的效率值可能更低，但所有測試電機(jī)的平均值均顯示為銘牌上的標(biāo)稱效率值。因此，額定效率 92.1 本質(zhì)上表示這是該電機(jī)型號(hào)的平均效率，但實(shí)際效率可能會(huì)有所不同。

任何形式的熱量都會(huì)降低效率，包括摩擦、定子繞組損耗、轉(zhuǎn)子損耗、鐵芯損耗（磁滯和渦流）等。制造商保證電機(jī)的實(shí)際效率在該標(biāo)稱效率的某個(gè)范圍內(nèi)。效率范圍因制造商而異。NEMA 規(guī)定的最大允許“范圍”為 20%。這是一個(gè)很大的范圍；因此，請密切關(guān)注制造商的實(shí)際最低保證！

# 17: FULL LOAD NOMINAL EFFICIENCY

Efficiency is defined as the ratio of the power output divided by the power input. Machine losses are in the form of heat, and include stator winding loss, rotor loss, core loss (hysteresis and eddy current), friction and windage, and stray load loss.

NEMA standard MG1-12.54.2 provides instructions for establishing the value of efficiency. The standard states that the nominal efficiency shown on the nameplate shall not be greater than the average efficiency of a large population of motors of the same design. Also, the full load efficiency, when operating at rated voltage and frequency, will not be less than the minimum value associated with the nominal value.

Care should be taken in comparing efficiencies from one motor manufacturer to another. It is difficult to compare efficiencies based on published, quoted or test data, due to the fact that there is no single standard method which is used throughout the industry. The most common referred to standards are IEEE 112 (U.S.), IEC (International), JEC-27 (Japanese), BS-269 (British) and ANSI C50.20 (same as IEEE 112). IEEE 112 is used more than any of the others in the United States, while allowing for a variety of test methods to be used. The preferred procedure is IEEE method B, where the motor is operated at full load, and the power is directly measured.

Generally, larger motors will be more efficient than smaller motors. Today's premium efficiency 3-phase motors have efficiencies ranging from 86.5% at 1 hp to 95.8% at 300 hp. The efficiency value that appears on the nameplate is the “nominal full-load efficiency” as determined using a very accurate dynamometer and a procedure described by IEEE Standard 112, Method B. The nominal value is what the average would be if a substantial number of identical motors were tested and the averages of the batch were determined. Some motors might have a higher value and others might be lower, but the average of all units tested is shown as the nominal nameplate value. Thus, essentially the rating Nom Eff. 92.1 means this is an average efficiency of this motor model, but actual efficiency may vary.

The efficiency is reduced by any form of heat, including friction, stator winding loss, rotor loss, core loss (hysteresis and eddy current), etc. The actual motor efficiency is guaranteed to be within a band of this nominal efficiency by the manufacturer. The efficiency band varies from manufacturer to manufacturer. The maximum allowable "band" is 20% set by NEMA. This is a large range; therefore pay close attention to the manufacturer's actual minimum guarantee!

# 18：機(jī)座尺寸（可選）

大多數(shù)電機(jī)尺寸都已標(biāo)準(zhǔn)化，并根據(jù)機(jī)座尺寸編號(hào)和字母名稱進(jìn)行分類。該系統(tǒng)由美國電氣制造商協(xié)會(huì) (NEMA) 開發(fā)，并根據(jù)外殼尺寸、馬力和轉(zhuǎn)速為標(biāo)準(zhǔn)電機(jī)額定值分配特定的機(jī)座尺寸。編號(hào)描述了安裝尺寸，包括底孔安裝方式、軸徑、軸高等。但是，它并未定義電機(jī)總長度和高度、接線盒延伸長度等。

目前，整馬力異步電機(jī)的標(biāo)準(zhǔn)化機(jī)座尺寸范圍為143T至445T。這些標(biāo)準(zhǔn)涵蓋了功率在100至200馬力范圍內(nèi)的大多數(shù)電機(jī)。

用于表示機(jī)座尺寸的數(shù)字根據(jù)電機(jī)的物理尺寸具有特定含義。前兩位數(shù)字與電機(jī)軸高有關(guān)，其余一位或多位數(shù)字與電機(jī)長度有關(guān)。根據(jù)經(jīng)驗(yàn)，可以通過將機(jī)座尺寸的前兩位數(shù)字除以 4 來計(jì)算臥式電機(jī)的軸高（以英寸為單位，“D”尺寸）。請注意，這適用于所有143T至445T機(jī)架尺寸的底座式 NEMA 機(jī)架電機(jī)。

機(jī)架尺寸的第三位數(shù)字與電機(jī)長度有關(guān)，但并沒有簡單易行的經(jīng)驗(yàn)法則。

需要注意的是，當(dāng)標(biāo)準(zhǔn)底座式電機(jī)的機(jī)架尺寸僅在第三位數(shù)字上有所不同時(shí)，軸直徑、軸長度以及從軸端到電機(jī)軸端底座螺栓孔的距離將相同。

以上示例中的長度差異發(fā)生在尺寸A和B所示的底座之間。后綴 T 表示電機(jī)機(jī)架分配符合現(xiàn)行標(biāo)準(zhǔn)，即所謂的“T”機(jī)架“Nu-Rate”標(biāo)準(zhǔn)，該標(biāo)準(zhǔn)于1964年采用。

請注意，機(jī)架尺寸僅指安裝尺寸，與電機(jī)殼體直徑無直接關(guān)系。通常，隨著機(jī)架號(hào)的增加，電機(jī)的物理尺寸和馬力也會(huì)增加。很多相同馬力的電機(jī)都采用不同的機(jī)座號(hào)。

使用公制電機(jī)（IEC 型）時(shí)，其概念與上述相同，但有一點(diǎn)不同：現(xiàn)在軸距底座的高度以毫米而非英寸表示。機(jī)座號(hào)指的是軸距底座的高度，以毫米為單位。（詳情將在本文的后面部分進(jìn)一步介紹）。

一些常見的機(jī)座號(hào)示例包括：

有關(guān)更多標(biāo)準(zhǔn)名稱，請參閱 NEMA MG 1-11.01。

# 18: FRAME SIZE (optional)

Most motor dimensions are standardized and categorized by a frame size number and letter designation. This system was developed by NEMA and specific frame sizes have been assigned to standard motor ratings based on enclosure, horsepower and speed. The number describes the mounting dimensions, including foot hole mounting pattern, shaft diameter, shaft height, etc. However, it does not define overall length and height, conduit box extension length, etc.

The current standardized frames for integral horsepower induction motors ranges from 143T to 445T. These standards cover most motors in the range of one through two hundred horsepower.

The numbers used to designate frame sizes have specific meanings based on the physical size of the motor. The first two digits are related to the motor shaft height and the remaining digit or digits relate to the length of the motor. As a rule of thumb, you can calculate the shaft height on horizontal motors in inches, (“D” dimension), by dividing the first two digits of the frame size by four. Please note that this works on all foot-mounted NEMA frame motors in 143T through 445T frames.

The third digit of the frame size is related to the length of the motor but there is no rule of thumb that can be easily applied.

It is important to note that when standard foot-mounted motors have frame sizes that differ only in the third digit, the shaft diameters, shaft lengths, and distance from the end of the shaft to the bolt holes in the feet on the shaft end of the motor will be the same.

The length difference in the examples above occurs between the feet as shown by dimensions A and B. The suffix T indicates that the motor frame assignment conforms to the current, or so called “T” frame “Nu-Rate” standards which were adopted in 1964.

Note that the frame size refers to mounting only and has no direct bearing on the motor body diameter. In general, as a frame number becomes higher, so does the physical size of the motor and the horsepower. There are many motors of the same horsepower built in different frames.

When working with metric motors (IEC type), the concept is the same as noted above with one exception: the shaft height above the base is now noted in millimeters rather than inches. The frame size is the shaft height in millimeters. (The details are further described later in the course).

Some common frame examples include:

For further standard designations refer to NEMA MG 1- 11.01.

# 19：NEMA 設(shè)計(jì)字母

電機(jī)繞組和轉(zhuǎn)子設(shè)計(jì)的變化會(huì)改變感應(yīng)電機(jī)的性能特性。為了在應(yīng)用中保持一致性，NEMA 指定了通用電機(jī)的特定設(shè)計(jì)，這些電機(jī)具有特定的堵轉(zhuǎn)轉(zhuǎn)矩、極限轉(zhuǎn)矩、轉(zhuǎn)差率、啟動(dòng)電流或其他值。A、B、C 和 D 設(shè)計(jì)有標(biāo)準(zhǔn)定義。字母名稱描述了電機(jī)的轉(zhuǎn)矩和電流特性。

NEMA A 型電機(jī) 具有正常的啟動(dòng)轉(zhuǎn)矩，但啟動(dòng)電流較大。這適用于短時(shí)間重載的應(yīng)用。注塑機(jī)是此類電機(jī)的理想應(yīng)用。

NEMA B 型電機(jī) 具有正常的啟動(dòng)轉(zhuǎn)矩和較低的啟動(dòng)電流。這些電機(jī)是應(yīng)用最廣泛的設(shè)計(jì)，其堵轉(zhuǎn)轉(zhuǎn)矩足以啟動(dòng)各種工業(yè)機(jī)械，并且堵轉(zhuǎn)啟動(dòng)電流也適用于大多數(shù)電力系統(tǒng)。B 設(shè)計(jì)的一些應(yīng)用包括機(jī)床、風(fēng)扇和鼓風(fēng)機(jī)、壓縮機(jī)、削片機(jī)和離心泵。這些是最常見的電機(jī)類型。

NEMA C 型電機(jī) 具有高啟動(dòng)扭矩（約225%）和低啟動(dòng)電流。這些電機(jī)具有高堵轉(zhuǎn)扭矩和相對較高的滿載滑差。由于其高堵轉(zhuǎn)扭矩和高滿載滑差，它們特別適合啟動(dòng)重載，例如往復(fù)式壓縮機(jī)、加煤機(jī)、破碎機(jī)和磨粉機(jī)，以及容積泵。

NEMA D 型電機(jī) 具有高啟動(dòng)扭矩和低啟動(dòng)電流，但滑差較大。空載時(shí)，電機(jī)以較小的滑差運(yùn)行。當(dāng)施加峰值負(fù)載時(shí)，電機(jī)滑差會(huì)顯著增加，從而使設(shè)備能夠吸收能量。這降低了電氣系統(tǒng)提供的功率峰值，從而使功率需求更加均衡。這些電機(jī)可用于帶有重型飛輪的低速?zèng)_床或起重應(yīng)用。

# 19: NEMA DESIGN LETTER

Changes in motor windings and rotor design will alter the performance characteristics of induction motors. To obtain uniformity in application, NEMA has designated specific designs of general purpose motors having specified locked rotor torque, breakdown torque, slip, starting current, or other values. There are standard definitions for designs A, B, C and D. The letter designation describes the torque and current characteristics of the motor.

NEMA Design A motors have normal starting torques, but high starting currents. This is useful for applications with brief heavy overloads. Injection molding machines are a good application for this type of motor.

NEMA Design B motors have normal starting torque, with low starting current. These are the most widely used design, and have locked rotor torques adequate for starting a wide variety of industrial machines and locked rotor starting currents acceptable to most power systems. Some Design B applications would include machine tools, fans and blowers, compressors, chippers, and centrifugal pumps. These are the most common type of motors.

NEMA Design C motors have high starting torque (approximately 225%) and low starting current. These motors have high locked rotor torque and relatively high full load slip. They are especially suited for starting heavy loads such as reciprocating compressors, stokers, crushers and pulverizers, as well as positive displacement pumps due to their high locked rotor torques and high full load slip.

NEMA Design D motors have high starting torque and low starting current, but with high slip. At no load the motor operates with little slip. When peak load is applied, the motor slip increases appreciably, allowing the unit to absorb the energy. This reduces power peaks supplied by the electrical system, resulting in a more uniform power requirement. These motors may be used on applications like a low speed punch press with a heavy flywheel, or hoisting applications.

# 20：機(jī)殼類型

電機(jī)機(jī)殼必須保護(hù)繞組、軸承和其他機(jī)械部件免受潮濕、化學(xué)物質(zhì)、機(jī)械損壞和砂礫磨損的影響。NEMA 標(biāo)準(zhǔn) MG1-1.25 至 1.27 定義了 20 多種機(jī)殼類型，涵蓋開放式電機(jī)、全封閉式電機(jī)以及帶封裝或密封繞組的電機(jī)。最常見的機(jī)殼類型包括：

開放式防滴漏 (ODP)：允許空氣在繞組中循環(huán)冷卻，但防止液滴在與垂直方向成 15 度角的范圍內(nèi)滴入電機(jī)。通常用于相對清潔干燥的室內(nèi)應(yīng)用。

全封閉風(fēng)扇冷卻式 (TEFC)：阻止機(jī)架內(nèi)外空氣自由交換，但不完全密封機(jī)架。風(fēng)扇安裝在軸上，在運(yùn)行過程中將空氣推過機(jī)架，以幫助冷卻。肋狀機(jī)架的設(shè)計(jì)旨在增加冷卻表面積。 TEFC 型機(jī)殼是所有機(jī)殼中用途最廣泛的一種。它適用于泵、風(fēng)扇、壓縮機(jī)、通用工業(yè)皮帶傳動(dòng)裝置和直接連接設(shè)備。

全封閉無通風(fēng) (TENV)：與 TEFC 類似，但沒有冷卻風(fēng)扇，依靠對流冷卻。無通風(fēng)口，緊密封閉以防止空氣自由交換，但不密封。這類機(jī)殼適用于暴露于灰塵或潮濕環(huán)境中，但不適用于非常潮濕或危險(xiǎn)（爆炸性）場所。

全封閉風(fēng)冷 (TEAO)：專為軸裝風(fēng)扇或皮帶驅(qū)動(dòng)風(fēng)扇設(shè)計(jì)的防塵風(fēng)扇和鼓風(fēng)機(jī)電機(jī)。電機(jī)必須安裝在風(fēng)扇氣流范圍內(nèi)。

全封閉沖洗電機(jī) (TEWD)：設(shè)計(jì)用于承受高壓沖洗或其他高濕度或潮濕環(huán)境。適用于 TEAO、TEFC 和 TENV 型機(jī)殼。

全封閉、惡劣及惡劣環(huán)境電機(jī)：設(shè)計(jì)用于極度潮濕或化學(xué)環(huán)境，但不適用于危險(xiǎn)場所。

防爆外殼 (EXPL)：防爆電機(jī)是一種全封閉的機(jī)器，旨在承受電機(jī)外殼內(nèi)特定氣體或蒸汽的爆炸，并防止電機(jī)外部因火花、閃光或爆炸而著火。這些電機(jī)專為特定危險(xiǎn)用途而設(shè)計(jì)，例如含有氣體或危險(xiǎn)粉塵的環(huán)境。為了安全運(yùn)行，電機(jī)的最高工作溫度必須低于周圍氣體或蒸汽的燃點(diǎn)。防爆電機(jī)的設(shè)計(jì)、制造和測試均符合美國保險(xiǎn)商實(shí)驗(yàn)室 (UL) 的嚴(yán)格要求。

危險(xiǎn)場所 (HAZ)：危險(xiǎn)場所電機(jī)應(yīng)用根據(jù)存在的危險(xiǎn)環(huán)境類型、造成危險(xiǎn)的特定材料的特性、暴露于環(huán)境中的可能性以及對造成危險(xiǎn)的物質(zhì)而言被認(rèn)為安全的最高溫度水平進(jìn)行分類。

定義此信息的格式是國家電氣規(guī)范 (NFPA-70) 定義的類別、組別、分類和溫度代碼結(jié)構(gòu)。危險(xiǎn)場所定義如下：

1) I 類

? A 組：乙炔

? B 組：丁二烯、環(huán)氧乙烷、氫氣、環(huán)氧丙烷以及氫氣含量超過 30% 的人造氣體。

? C 組：乙醛、環(huán)丙烷、乙醚、乙烯。

? D 組：丙酮、丙烯腈、氨、苯、丁烷、乙醇、二氯乙烷、汽油、己烷、異戊二烯、甲烷（天然氣）、甲醇、石腦油、丙烷、丙烯、苯乙烯、甲苯、醋酸乙烯酯、氯乙烯、二甲苯。

2) II 類

? E 組：鋁、鎂及其他具有類似特性的金屬粉塵。

? F 組：炭黑、焦炭或煤塵。

? G 組：面粉、淀粉或谷物粉塵。

3) III 類

? 易燃纖維，例如人造絲、棉、劍麻、大麻、可可纖維、麻絮、細(xì)木工板以及其他類似性質(zhì)的材料。

NEMA外殼描述與IEC防護(hù)等級 (IP) 代碼類似。NEMA名稱更具描述性和通用性，而 IEC IP 代碼則更精確，采用兩位數(shù)代碼進(jìn)行嚴(yán)格定義，第一位數(shù)字表示電機(jī)對固體物體的防護(hù)程度，第二位數(shù)字表示電機(jī)對濕氣的防護(hù)程度。例如，NEMA“開放式防滴 (ODP)”電機(jī)對應(yīng) IP22，NEMA“全封閉”電機(jī)對應(yīng)IP54，NEMA“防風(fēng)雨”電機(jī)對應(yīng)IP45，NEMA“耐沖洗”電機(jī)對應(yīng)IP55。

# 20: ENCLOSURE TYPE

The enclosure of the motor must protect the windings, bearings, and other mechanical parts from moisture, chemicals, mechanical damage and abrasion from grit. NEMA standards MG1- 1.25 through 1.27 define more than 20 types of enclosures under the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed windings. The most common types of enclosures are:

Open Drip Proof (ODP): Allows air to circulate through the windings for cooling, but prevent drops of liquid from falling into motor within a 15 degree angle from vertical. Typically used for indoor applications in relatively clean, dry locations.

Totally Enclosed Fan Cooled (TEFC): Prevents the free exchange of air between the inside and outside of the frame, but does not make the frame completely airtight. A fan is attached to the shaft and pushes air over the frame during its operation to help in the cooling process. The ribbed frame is designed to increase the surface area for cooling purposes. The TEFC style enclosure is the most versatile of all. It is used on pumps, fans, compressors, general industrial belt drive and direct connected equipment.

Totally Enclosed Non-Ventilated (TENV): Similar to a TEFC, but has no cooling fan and relies on convection for cooling. No vent openings, tightly enclosed to prevent the free exchange of air, but not airtight. These are suitable for uses which are exposed to dirt or dampness, but not very moist or hazardous (explosive) locations.

Totally Enclosed Air Over (TEAO): Dust-tight fan and blower duty motors designed for shaft mounted fans or belt driven fans. The motor must be mounted within the airflow of the fan.

Totally Enclosed Wash down (TEWD): Designed to withstand high pressure wash-downs or other high humidity or wet environments. Available on TEAO, TEFC and TENV enclosures.

Totally enclosed, hostile and severe environment motors: Designed for use in extremely moist or chemical environments, but not for hazardous locations.

Explosion-proof enclosures (EXPL): The explosion proof motor is a totally enclosed machine and is designed to withstand an explosion of specified gas or vapor inside the motor casing and prevent the ignition outside the motor by sparks, flashing or explosion. These motors are designed for specific hazardous purposes, such as atmospheres containing gases or hazardous dusts. For safe operation, the maximum motor operating temperature must be below the ignition temperature of surrounding gases or vapors. Explosion proof motors are designed, manufactured and tested under the rigid requirements of the Underwriters Laboratories.

Hazardous Location (HAZ): Hazardous location motor applications are classified by the type of hazardous environment present, the characteristics of the specific material creating the hazard, the probability of exposure to the environment, and the maximum temperature level that is considered safe for the substance creating the hazard.

The format used to define this information is a class, group, division and temperature code structure as defined by the National Electric Code (NFPA-70). The following hazardous locations are defined:

1) CLASS I

? Group A: Acetylene

? Group B: Butadiene, ethylene oxide, hydrogen, propylene oxide, manufactured gases containing more than 30% hydrogen by volume.

? Group C: Acetaldehyde, cyclopropane, diethyl ether, ethylene.

? Group D: Acetone, acrylonitrile, ammonia, benzene, butane, ethanol, ethylene dichloride, gasoline, hexane, isoprene, methane (natural gas), methanol, naphtha, propane, propylene, styrene, toluene, vinyl acetate, vinyl chloride, xylene.

2) CLASS II

? Group E: Aluminum, magnesium, and other metal dusts with similar characteristics.

? Group F: Carbon black, coke or coal dust.

? Group G: Flour, starch or grain dust.

3) CLASS III

? Easily ignitable fibers, such as rayon, cotton, sisal, hemp, cocoa fiber, oakum, excelsior and other materials of similar nature.

The NEMA enclosure description is similar to the IEC Index of Protection (IP) code. The NEMA designations are more descriptive and general, whereas the IEC IP codes are more precise and narrowly defined by a 2-digit code, with the first digit defining how well protected the motor is from solid objects and the second digit describing how well protected the motor is from moisture. For example, a NEMA "Open Drip Proof (ODP)" motor corresponds to an IP22 and a NEMA "Totally Enclosed" motor corresponds to an IP54, a NEMA "Weather-Proof" motor to an IP45, and a NEMA "Wash-Down" motor to an IP55.

# 21：熱保護(hù)

熱保護(hù)是指電機(jī)的過熱保護(hù)功能（如有配備）。熱保護(hù)包括以下幾種：

自動(dòng)（自動(dòng)復(fù)位）：包含溫度傳感裝置，如果因啟動(dòng)失敗或過載導(dǎo)致溫度過高，該裝置會(huì)斷開電源的一側(cè)。電機(jī)冷卻后，熱保護(hù)器會(huì)自動(dòng)恢復(fù)供電。請勿在意外重啟可能造成危險(xiǎn)的場合使用。

阻抗（阻抗）：根據(jù) UL 標(biāo)準(zhǔn) No. 519，電機(jī)設(shè)計(jì)使其在堵轉(zhuǎn)（失速）情況下不會(huì)在 15 天內(nèi)燒壞。

手動(dòng)（手動(dòng)復(fù)位）：包含溫度傳感裝置，如果因啟動(dòng)失敗或過載導(dǎo)致溫度過高，該裝置會(huì)斷開電源的一側(cè)。電機(jī)冷卻后，必須按下外部按鈕才能恢復(fù)供電。嘗試復(fù)位電機(jī)保護(hù)器前，請先關(guān)閉電源。在意外重啟可能造成危險(xiǎn)的場合，例如鋸子、傳送帶、壓縮機(jī)等，優(yōu)先選擇這種裝置。

無：電機(jī)不包含溫度傳感器，用于防止電機(jī)因啟動(dòng)失敗或過載而過熱。電機(jī)應(yīng)根據(jù) NEC 和當(dāng)?shù)匾?guī)范要求采用其他保護(hù)措施。

T-St（溫控器）：安裝在電機(jī)內(nèi)部的溫度傳感器，并引出單獨(dú)的導(dǎo)線連接到電機(jī)啟動(dòng)器先導(dǎo)電路。在啟動(dòng)失敗或過載情況下，溫控器觸點(diǎn)將斷開。電機(jī)冷卻后，溫控器觸點(diǎn)將自動(dòng)重新閉合。

# 21: THERMAL PROTECTION

Thermal protection describes the motor’s over temperature protection, if so equipped. Thermal protection can include the following:

Auto (Automatic Reset): Contains temperature-sensing device that disconnects one leg of its power source if temperature becomes excessive due to failure-to-start or overload. After motor cools, thermal protector automatically restores power. Should not be used where unexpected re-starting would be hazardous

Imp (Impedance): Motor is designed so that it will not burn out in less than 15 days under locked rotor (stalled) conditions, in accordance with UL standard No. 519.

Man (Manual Reset): Contains a temperature-sensing device that disconnects one leg of its power source if temperature becomes excessive due to failure-to-start or overload. After motor cools, an external button must be pushed to restore power to the motor. Turn off power prior to attempting to reset motor protector. Preferred where unexpected re-starting would be hazardous, as on saws, conveyors, compressors, etc

None: Motor contains no temperature-sensing device to protect motor from excessive temperature due to failure-to-start or overload. Motor should be protected by other means in accordance with the NEC and local code requirements.

T-St (Thermostat): A temperature-sensing device installed inside the motor with separate leads brought out for connection into motor starter pilot circuit. Under failure-to-start or overload conditions, thermostat contacts will open. Thermostat contacts will reclose automatically when motor cools.

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