NEMA及IEC标准下的电机铭牌识别（连载四）

# 15：功率因数 (PF)

铭牌上的功率因数有时缩写为 PF 或 P.F。功率因数是有功功率 (W) 与视在功率 (VA) 之比，以百分比表示。功率因数也等于电流与电压之间滞后角的余弦值 (“Cos”)。

对于感应电机，功率因数会随负载而变化。空载时功率因数最小，随着电机负载的增加而增加。功率因数通常在电机满载或接近满载时达到峰值。

它的值范围为0到1，表示满载状态。功率因数最好接近 1 (100%)。可以通过添加电容器来提高功率因数。

在 NEMA 电机中，功率因数缩写为“PF”，在 IEC 电机中，功率因数标记为“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：服务系数 (SF)

电机服务系数 (SF) 是指电机在正确的电压容差范围内正常运行时，短时间内能够承受的过载百分比。它非常实用，因为它可以在估算功率需求和实际运行功率要求时提供一些“参考”。它还能降低额定负载下的绕组温度，防止间歇性温升，并有助于抵消低电压或不平衡的线路电压。例如，开放式防滴 (ODP) 电机的标准服务系数为1.15。这意味着，一台10马力、服务系数为1.15 的电机，在短期使用时可以提供11.5马力的功率。一些小功率电机的服务系数更高，例如1.25、1.35 甚至1.50。

NEMA 将服务系数定义为一个乘数，当它应用于额定马力时，表示在额定电压和频率下，在服务系数规定的条件下可以承载的允许马力负载。该服务系数可用于以下用途：

1. 弥补预测间歇性系统马力需求的不准确性。

2. 通过降低额定负载下的绕组温度来延长绝缘寿命。

3. 处理间歇性或偶尔的过载。

4. 允许环境温度偶尔高于40°C。

5. 补偿低电压或不平衡电源电压。

然而，NEMA 在讨论服务系数时也增加了一些注意事项：

1. 长时间以服务系数负载运行通常会降低电机转速、寿命和效率。

2. 电机可能无法提供足够的启动和拉出扭矩，并且启动器/过载尺寸可能不正确。这反过来会影响电机的整体寿命。

3. 切勿依赖服务系数来持续承载负载。

4. 服务系数是在额定电压、频率、环境温度和海平面条件下运行而确定的。

大多数电机的开式电机占空比为1.15，全封闭式电机占空比为1.0。传统上，全封闭风冷 (TEFC) 电机的服务系数为1.0，但现在大多数制造商提供的TEFC 电机的服务系数为1.15，与ODP 电机相同。大多数危险场所电机的服务系数为1.0，但某些用于 I 类应用的专用电机的服务系数为1.15。

只有当服务系数高于1.0时，才需要在铭牌上注明。

# 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：满载标称效率

效率定义为输出功率与输入功率之比。电机损耗以热量的形式存在，包括定子绕组损耗、转子损耗、铁芯损耗（磁滞和涡流）、摩擦和风阻以及杂散负载损耗。

NEMA标准MG1-12.54.2提供了确定效率值的说明。该标准规定，铭牌上显示的标称效率不得高于相同设计的大量电机的平均效率。此外，在额定电压和频率下运行时，满载效率不得低于与标称效率相关的最小值。

在比较不同电机制造商的效率时应谨慎。由于整个行业没有统一的标准方法，因此很难基于已发布、引用或测试数据来比较效率。最常参考的标准是IEEE 112（美国）、IEC（国际）、JEC-27（日本）、BS-269（英国）和 ANSI C50.20（与 IEEE 112 相同）。IEEE 112 在美国的应用最为广泛，同时允许使用多种测试方法。首选的测试程序是IEEE方法B，即电机满载运行，并直接测量功率。

通常，大型电机的效率高于小型电机。如今，高效三相电机的效率范围从1马力时的86.5%到300马力时的95.8%。铭牌上显示的效率值是“标称满载效率”，该效率值是使用高精度测功机按照 IEEE 标准 112 方法 B 中规定的程序测定的。标称效率是指对大量相同电机进行测试并确定该批次电机平均值后所得的平均值。有些电机的效率值可能更高，有些电机的效率值可能更低，但所有测试电机的平均值均显示为铭牌上的标称效率值。因此，额定效率 92.1 本质上表示这是该电机型号的平均效率，但实际效率可能会有所不同。

任何形式的热量都会降低效率，包括摩擦、定子绕组损耗、转子损耗、铁芯损耗（磁滞和涡流）等。制造商保证电机的实际效率在该标称效率的某个范围内。效率范围因制造商而异。NEMA 规定的最大允许“范围”为 20%。这是一个很大的范围；因此，请密切关注制造商的实际最低保证！

# 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：机座尺寸（可选）

大多数电机尺寸都已标准化，并根据机座尺寸编号和字母名称进行分类。该系统由美国电气制造商协会 (NEMA) 开发，并根据外壳尺寸、马力和转速为标准电机额定值分配特定的机座尺寸。编号描述了安装尺寸，包括底孔安装方式、轴径、轴高等。但是，它并未定义电机总长度和高度、接线盒延伸长度等。

目前，整马力异步电机的标准化机座尺寸范围为143T至445T。这些标准涵盖了功率在100至200马力范围内的大多数电机。

用于表示机座尺寸的数字根据电机的物理尺寸具有特定含义。前两位数字与电机轴高有关，其余一位或多位数字与电机长度有关。根据经验，可以通过将机座尺寸的前两位数字除以 4 来计算卧式电机的轴高（以英寸为单位，“D”尺寸）。请注意，这适用于所有143T至445T机架尺寸的底座式 NEMA 机架电机。

机架尺寸的第三位数字与电机长度有关，但并没有简单易行的经验法则。

需要注意的是，当标准底座式电机的机架尺寸仅在第三位数字上有所不同时，轴直径、轴长度以及从轴端到电机轴端底座螺栓孔的距离将相同。

以上示例中的长度差异发生在尺寸A和B所示的底座之间。后缀 T 表示电机机架分配符合现行标准，即所谓的“T”机架“Nu-Rate”标准，该标准于1964年采用。

请注意，机架尺寸仅指安装尺寸，与电机壳体直径无直接关系。通常，随着机架号的增加，电机的物理尺寸和马力也会增加。很多相同马力的电机都采用不同的机座号。

使用公制电机（IEC 型）时，其概念与上述相同，但有一点不同：现在轴距底座的高度以毫米而非英寸表示。机座号指的是轴距底座的高度，以毫米为单位。（详情将在本文的后面部分进一步介绍）。

一些常见的机座号示例包括：

有关更多标准名称，请参阅 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 设计字母

电机绕组和转子设计的变化会改变感应电机的性能特性。为了在应用中保持一致性，NEMA 指定了通用电机的特定设计，这些电机具有特定的堵转转矩、极限转矩、转差率、启动电流或其他值。A、B、C 和 D 设计有标准定义。字母名称描述了电机的转矩和电流特性。

NEMA A 型电机 具有正常的启动转矩，但启动电流较大。这适用于短时间重载的应用。注塑机是此类电机的理想应用。

NEMA B 型电机 具有正常的启动转矩和较低的启动电流。这些电机是应用最广泛的设计，其堵转转矩足以启动各种工业机械，并且堵转启动电流也适用于大多数电力系统。B 设计的一些应用包括机床、风扇和鼓风机、压缩机、削片机和离心泵。这些是最常见的电机类型。

NEMA C 型电机 具有高启动扭矩（约225%）和低启动电流。这些电机具有高堵转扭矩和相对较高的满载滑差。由于其高堵转扭矩和高满载滑差，它们特别适合启动重载，例如往复式压缩机、加煤机、破碎机和磨粉机，以及容积泵。

NEMA D 型电机 具有高启动扭矩和低启动电流，但滑差较大。空载时，电机以较小的滑差运行。当施加峰值负载时，电机滑差会显著增加，从而使设备能够吸收能量。这降低了电气系统提供的功率峰值，从而使功率需求更加均衡。这些电机可用于带有重型飞轮的低速冲床或起重应用。

# 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：机壳类型

电机机壳必须保护绕组、轴承和其他机械部件免受潮湿、化学物质、机械损坏和砂砾磨损的影响。NEMA 标准 MG1-1.25 至 1.27 定义了 20 多种机壳类型，涵盖开放式电机、全封闭式电机以及带封装或密封绕组的电机。最常见的机壳类型包括：

开放式防滴漏 (ODP)：允许空气在绕组中循环冷却，但防止液滴在与垂直方向成 15 度角的范围内滴入电机。通常用于相对清洁干燥的室内应用。

全封闭风扇冷却式 (TEFC)：阻止机架内外空气自由交换，但不完全密封机架。风扇安装在轴上，在运行过程中将空气推过机架，以帮助冷却。肋状机架的设计旨在增加冷却表面积。 TEFC 型机壳是所有机壳中用途最广泛的一种。它适用于泵、风扇、压缩机、通用工业皮带传动装置和直接连接设备。

全封闭无通风 (TENV)：与 TEFC 类似，但没有冷却风扇，依靠对流冷却。无通风口，紧密封闭以防止空气自由交换，但不密封。这类机壳适用于暴露于灰尘或潮湿环境中，但不适用于非常潮湿或危险（爆炸性）场所。

全封闭风冷 (TEAO)：专为轴装风扇或皮带驱动风扇设计的防尘风扇和鼓风机电机。电机必须安装在风扇气流范围内。

全封闭冲洗电机 (TEWD)：设计用于承受高压冲洗或其他高湿度或潮湿环境。适用于 TEAO、TEFC 和 TENV 型机壳。

全封闭、恶劣及恶劣环境电机：设计用于极度潮湿或化学环境，但不适用于危险场所。

防爆外壳 (EXPL)：防爆电机是一种全封闭的机器，旨在承受电机外壳内特定气体或蒸汽的爆炸，并防止电机外部因火花、闪光或爆炸而着火。这些电机专为特定危险用途而设计，例如含有气体或危险粉尘的环境。为了安全运行，电机的最高工作温度必须低于周围气体或蒸汽的燃点。防爆电机的设计、制造和测试均符合美国保险商实验室 (UL) 的严格要求。

危险场所 (HAZ)：危险场所电机应用根据存在的危险环境类型、造成危险的特定材料的特性、暴露于环境中的可能性以及对造成危险的物质而言被认为安全的最高温度水平进行分类。

定义此信息的格式是国家电气规范 (NFPA-70) 定义的类别、组别、分类和温度代码结构。危险场所定义如下：

1) I 类

• A 组：乙炔

• B 组：丁二烯、环氧乙烷、氢气、环氧丙烷以及氢气含量超过 30% 的人造气体。

• C 组：乙醛、环丙烷、乙醚、乙烯。

• D 组：丙酮、丙烯腈、氨、苯、丁烷、乙醇、二氯乙烷、汽油、己烷、异戊二烯、甲烷（天然气）、甲醇、石脑油、丙烷、丙烯、苯乙烯、甲苯、醋酸乙烯酯、氯乙烯、二甲苯。

2) II 类

• E 组：铝、镁及其他具有类似特性的金属粉尘。

• F 组：炭黑、焦炭或煤尘。

• G 组：面粉、淀粉或谷物粉尘。

3) III 类

• 易燃纤维，例如人造丝、棉、剑麻、大麻、可可纤维、麻絮、细木工板以及其他类似性质的材料。

NEMA外壳描述与IEC防护等级 (IP) 代码类似。NEMA名称更具描述性和通用性，而 IEC IP 代码则更精确，采用两位数代码进行严格定义，第一位数字表示电机对固体物体的防护程度，第二位数字表示电机对湿气的防护程度。例如，NEMA“开放式防滴 (ODP)”电机对应 IP22，NEMA“全封闭”电机对应IP54，NEMA“防风雨”电机对应IP45，NEMA“耐冲洗”电机对应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：热保护

热保护是指电机的过热保护功能（如有配备）。热保护包括以下几种：

自动（自动复位）：包含温度传感装置，如果因启动失败或过载导致温度过高，该装置会断开电源的一侧。电机冷却后，热保护器会自动恢复供电。请勿在意外重启可能造成危险的场合使用。

阻抗（阻抗）：根据 UL 标准 No. 519，电机设计使其在堵转（失速）情况下不会在 15 天内烧坏。

手动（手动复位）：包含温度传感装置，如果因启动失败或过载导致温度过高，该装置会断开电源的一侧。电机冷却后，必须按下外部按钮才能恢复供电。尝试复位电机保护器前，请先关闭电源。在意外重启可能造成危险的场合，例如锯子、传送带、压缩机等，优先选择这种装置。

无：电机不包含温度传感器，用于防止电机因启动失败或过载而过热。电机应根据 NEC 和当地规范要求采用其他保护措施。

T-St（温控器）：安装在电机内部的温度传感器，并引出单独的导线连接到电机启动器先导电路。在启动失败或过载情况下，温控器触点将断开。电机冷却后，温控器触点将自动重新闭合。

# 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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