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HQ 965408

August 22, 2002

CLA-2 RR:CR:GC 965408 HEF


TARIFF NO.: 8533.29.00

Mr. James K. Kearney
Reed Smith, LLP
1301 K Street, N.W.
Suite 1100 – East Tower
Washington, DC 20005

RE: Polymeric PTC Thermistor Circuit Protectors (PolySwitch®)

Dear Mr. Kearney:

This is in response to your letter dated December 3, 2001, to the Director, National Commodity Specialist Division, New York, on behalf of Raychem Circuit Protection, an operating unit of Tyco Electronics Corporation, requesting the classification of Polymeric PTC Thermistor Circuit Protectors (PolySwitch®) under the Harmonized Tariff Schedule of the United States (HTSUS). Your letter was referred to this office for reply. Samples, representing eighteen types of PolySwitch® devices, were submitted. In preparing this ruling, consideration was given to your supplemental submissions of March 1, March 12, April 30, July 15, and August 5, 2002.


PolySwitch® devices are manufactured in radial-leaded, surface-mount, axial-leaded or chip part designs. These devices are functionally tailored to the specific requirements of the diverse applications in which the devices will be used. PolySwitch® devices have a conductive polymer composition, which acts to increase the electrical resistance of the device as its temperature increases. This result is commonly known as the Positive Temperature Coefficient (PTC) effect. The PTC effect limits the flow of the current to a point where only a “trickle” of electricity still flows in order to protect sensitive electronics such as solid-state (silicon-based) integrated circuits. When the temperature decreases below its designated “trip” point, the resistance of the device reverts back to its original state.

PolySwitch® devices have two primary uses. They can be placed in a series and used as an overcurrent protector or they can be used as temperature sensors to protect sensitive electrical components from damage when the application exceeds a defined temperature.


Whether the merchandise is classified as an electrical resistor, under heading 8533, HTSUS, or as an electrical apparatus for switching or protecting electrical circuits under, heading 8536, HTSUS.


Classification under the HTSUS is made in accordance with the General Rules of Interpretation (GRIs). GRI 1 provides that the classification of goods shall be determined according to the terms of the headings of the tariff schedule and any relative Section or Chapter Notes. In the event that the goods cannot be classified solely on the basis of GRI 1, and if the headings and legal notes do not otherwise require, the remaining GRIs may then be applied.

In understanding the language of the HTSUS, the Harmonized Commodity Description and Coding System Explanatory Notes (ENs) may be utilized. ENs, though not dispositive or legally binding, provide commentary on the scope of each heading of the HTSUS, and are the official interpretation of the Harmonized System at the international level. Customs believes the ENs should always be consulted. See T.D. 89-80, 54 Fed. Reg. 35127, 35128 (August 23, 1989).

The HTSUS provisions under consideration are as follows:

8533 Electrical resistors (including rheostats and potentiometers), other than heating resistors; parts thereof:


Electrical apparatus for switching or protecting electrical circuits, or for making connections to or in electrical circuits (for example, switches, relays, fuses, surge suppressors, plugs, sockets, lamp-holders, junction boxes), for a voltage not exceeding 1,000 V:

8536.30 Other apparatus for protecting electrical circuits:

8536.30.80 Other.

EN 85.33 (A) explains how resistors operate as follows: “These are conductors whose function is to provide a given electrical resistance in a circuit (e.g., limit the current flowing).” EN 85.33 (A) states, in pertinent part:

Resistors (resistances). These are conductors whose function is to provide a given electrical resistance in a circuit (e.g., to limit the current flowing). They vary greatly in size and shape, and in the materials of which they are made. They may be made of metals (in the form of bars, shapes or wire, often coiled in bobbins) or of carbon in the form of rods, or of carbon, silicon carbide, metal or metal oxide film. They may be obtained in the form of individual components by a printing process. Certain resistors may be fitted with a number of terminals allowing the whole or part to be included in the circuit.

The heading includes:

(5) Non-linear resistors: depending on temperature (thermistors) with a negative or positive temperature coefficient (usually mounted in glass tubes), and non-linear resistors depending on voltage (varistors/VDR), but not including varistor diodes of heading 85.41.

PolySwitch® is a thermistor, which detects the heat produced when a high current surge flows across its terminals. As the temperature increases, the device’s resistance increases. A logarithmic increase in resistance reduces the surge current to within safe levels. A “latching” characteristic maintains the device in a state of high resistance until the fault is removed and the temperature decreases. Once cool, the circuit will revert to operating in its normal condition. During this process, the flow of current is reduced to a trickle, but it is never completely broken.

Heading 8533, HTSUS, is an eo nomine classification provision for electrical resistors. An eo nomine provision is one that describes a commodity by a specific name, as opposed to use. The name is usually one common in commerce. Absent limiting language or indicia of contrary legislative intent, such a provision covers all forms of the article. See National Advanced Sys. v. United States, 26 F.3d 1107, 1111 (Fed. Cir. 1994). McGraw-Hill Encyclopedia of Science and Technology, 7th ed., (McGraw-Hill, Inc., New York, 1992), defines thermistors on page 292 as electrical resistors. Moreover, it lists their typical uses: “Thermistors are useful for measuring temperature and gas flow or wind velocity. Often they are employed as bolometer elements to measure radio-frequency, microwave, and optical power. They also are used as electrical circuit components for temperature compensation, voltage regulation, circuit protection, time delay, and volume control.”

Customs has classified other products which protect electronic equipment against current surges in heading 8533, HTSUS. See HQ 084651, dated August 2, 1989, and HQ 081600, dated September 21, 1989, which respectively classified zinc oxide varistors and metal oxide varistors exhibiting symmetrical, non-linear, voltage-current characteristics and used in large part for protecting electronic components against voltage surges in subheading 8533.40.00, HTSUS. See HQ 953765, dated October 1, 1993, which classified a sending unit, which acts as an electrical sensor to indicate the position of an outboard motor on a speedboat in subheading 8533.40.00, HTSUS. The sending unit’s rheostat would rotate and change the resistance in the circuit in order to determine the angular position of the engine.

Heading 8536, HTSUS, provides for “electrical apparatus for switching or protecting electrical circuits, or for making connections in electrical circuitsfor a voltage not exceeding 1,000 V.” The instant goods are used in larger apparatus to “protect” electronic components. Heading 8536, HTSUS, describes the class of merchandise to which thermistors belong and the use to which they are put.

However, the items classified under heading 8536, HTSUS, break the flow of current in order to protect the electrical apparatus. EN 8536 (II) states, “This heading includes other devices for preventing overload of circuits (e.g., electro-magnetic devices which automatically break the circuit when the current exceeds a certain value).” See HQ 089927, dated October 10, 1991, classifying CMC Terminations used to temporarily terminate or close an electrical circuit in circuits under 1,000 V under heading 8536, HTSUS.

On page 1 of Raychem’s “Technical Paper: Fundamentals of Resettable Functionality in PPTC Devices (2002), the operating differences between resettable fuses and PolySwitch® devices are described:

Fuses are current interruption devices, and once a fuse “blows”, the electrical circuit is broken, and there is no longer current flowing through the fuse. This electrical interruption (or open circuit) is a permanent condition. However, once a PPTC device trips, there is a small amount of current flowing through the device. PPTC devices require a low joule heating leakage current or external heat source in order to maintain their tripped condition. Once the fault condition is removed, this heat source is eliminated. The device can then return to a low resistance status and the circuit is restored.

Both headings appear to describe the goods as to function. When goods cannot be classified by applying GRI 1, and if the headings and legal notes do not otherwise require, the remaining GRI's are applied. GRI 3 states, in pertinent part, that when goods are, prima facie, classifiable under two or more headings, classification shall be effected as follows: “(a) The heading which provides the most specific description shall be preferred to headings providing a more general description.” EN (IV)(a) to GRI 3(a) states, in pertinent part: “A description by name is more specific than a description by class.” Resistors is an eo nomine provision. Thermistors are a type of resistor; the goods fit this more narrow description of heading 8533, HTSUS, and the goods are classified therein.

Thus, the subject merchandise’s proper classification is under subheading 8533.29.00, HTSUS, which provides for electrical resistors (including rheostats and potentiometers), other than heating resistors; parts thereofother.


The PolySwitch® devices are classifiable in subheading 8533.29.00, HTSUS, which provides for electrical resistors (including rheostats and potentiometers), other than heating resistors; parts thereofother.


Myles B. Harmon, Acting Director Commercial Rulings Division

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