For the black Featherweights, Singer had two different connection types.  They aren't interchangeable, so this article can be a reference when checking the compatibility of the machine and cord.  

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Round Pin Plug and Terminal:

The round pin terminals and plugs were used exclusively in the USA, but they can also be seen on most Featherweights sold in Canada, and Featherweights marketed to Europe prior to about 1951.

 

The photos above show how the cords come out of the top of the plug, and the two halves of the plug are held together by two screws and nuts.

A look inside the plug shows the intricacies of the wiring and the components that make connection to the terminal.   

Flat Prong Plug and Terminal:

The flat prong terminals and plugs were used on most black Featherweights sold in the UK, Europe, and Australia.  In the UK and Europe Singer started using this configuration in 1951 just prior to the release of the 222K Featherweight in 1953.    

It is common to see these terminals equipped with either bakelite nuts or brass slotted nuts at the connection points in the back.

To open the flat prong plug for rewiring, these small metal rings must first be removed.  

The cords on the flat prong plugs do come out the side, and the wires on the inside are held in place by small screws instead of the brass caps and nuts in the round pin plug.  Singer uses the same wiring pattern for both the round pin and flat prong plugs.

This oddly-shaped flat prong plug can be sometimes be seen with the 221 and 222; it is designed with an extra spot for a grounding wire.

Most all flat prong plugs were used in conjunction with machines fitted with the top light switch shown in the "221K4" diagram above.

Broken Terminals:

It is a fairly common occurrence that the terminal on the machine will be broken.  That is almost always caused by the machine being hit against the case as it is put away.  Click here to read how to properly pack and store the Featherweight in its case.

Click here to order a replacement terminal.

The Featherweight 221 machines manufactured from 1933 into 1936 had an opening in the base below the terminal, so they are more susceptible to this damage.

This article can quickly help match the proper cord set to the correct machine terminal.  To see how to wire the machine to its terminal, use the following links to our video tutorial and the Featherweight service manual:

How to Replace the Electrical Components of a Singer Featherweight

Featherweight 221 Service Manual

Further reading:

How to Fix Terminal Pins for a Better Connection

Types of Electrical Plugs

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Introduction

This article takes an in-depth look at the types of electrical plugs.

Read further and learn more about topics such as:

• What are Electrical Plugs
• Two-pronged and Three-pronged Plugs
• Types of Electrical Plugs
• Plug Adapters and Replacement Plugs
• And much more...

Chapter 1: What are Electrical Plugs?

Electrical plugs, commonly known as power plugs, are devices responsible for supplying and drawing current from a receptacle to the circuitry of an electrical appliance.

Electrical plugs consist of prongs or pins supported by plastic support or casing. Prongs are inserted into the holes of an outlet or receptacle to establish the electrical connection between the appliance and the main power supply.

Many types of standard electrical plugs are found in residences, industries, and commercial spaces worldwide. Electrical plugs differ in the number and dimensions of the pins, voltage and current ratings, and countries in which they are used.

Chapter 2: Two-Pronged and Three-Pronged Plugs

Electrical plugs have two or three prongs:

Two-Pronged Plugs

Two-pronged plugs have one prong or pin, each connected to the “hot” and “neutral” slots of the receptacle. The hot pin is connected to the hot slot of the socket. It draws current from the receptacle, which flows to power the load. The neutral pin, connected to the neutral slot of the socket, returns the current to the receptacle and back to the power supply. Two-pronged plugs can be readily inserted into two-slot receptacles.

Three-Pronged Plugs

In three-pronged plugs, a grounding or earthing pin is introduced. This pin is connected to an electrical system's ground wire. It is typically positioned under hot and neutral pins. This pin does not carry current, and the ground connection is added as a safety feature. In case of a faulty wire, short circuit, or electrical surge, the ground connection will transmit and neutralize the stray electricity to the power supply and the ground. Therefore, the ground connection can prevent electrocution, electrical fires, and damage to the plugged appliance. Moreover, installing three-slot receptacles is required nowadays in newly constructed buildings and residences.

Three-pronged plugs are used in electrical appliances requiring high power, such as flat irons, toasters, HVAC equipment, industrial machinery, and other sensitive electronics. They are used for devices contained in a metal housing (e.g., computers and game consoles). Stray electricity can conduct through the metal housing; thus, a ground connection can divert the path of the stray current instead of electrically shocking a person.

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Chapter 3: Types of Electrical Plugs

There are fifteen (15) standard types of mains electrical plugs worldwide recognized by the International Electrotechnical Commission (IEC). These types are listed in the IEC 60083 standard. Each type has a letter designation and lists under a standard, which we will be discussing in the succeeding sections.

NEMA Plugs (Type A, B)

NEMA plugs are compliant with the standards and specifications set by the National Electrical Manufacturers Association (NEMA), the largest trade association for electrical equipment and medical imaging equipment. NEMA standards are prevalent in North and Central America, but other countries also adopt these standards. NEMA designates Type A and Type B plugs.

Type A (NEMA 1-15) Plugs

Type A electrical plugs are ungrounded plugs that consist of two flat parallel prongs. These plugs have a current and voltage rating of 15A and 125V, respectively. The length of the pins varies from 15.9-18.3 mm, and their spacing is 12.7 mm.

Type A plugs have polarized and non-polarized versions. Polarized plugs have a neutral pin wider than the hot pin, limiting their insertion to only one orientation. Polarized Type A plugs are common in North America and Mexico. They have neutral and hot pins measuring 7.9 mm and 6.3 mm wide, respectively. Meanwhile, non-polarized plugs have prongs with equal widths. They are widely used in Japan. Non-polarized plugs can fit into polarized sockets, but not the other way around. Type A plugs are compatible with Types A and B sockets.

In type A plugs, there are holes present near the tip of the prongs. The bumps on the outlet’s contact wiper fill the prong holes as the prongs are inserted into the receptacle. This mechanism allows the outlet to grip the plug firmly and prevents it from slipping out due to its weight. In some special sockets, a rod can be inserted into these holes to lock the plug when it is inserted. These holes also enable factory sealing.

Some sockets use two spring-action blades instead of a contact wiper, which grip the prongs on their sides. This mechanism makes the holes unnecessary.

Type B (NEMA 5-15) Plug

Type B electrical plugs, also known as the North American 3-pin plug, are grounded plugs. They consist of two flat parallel prongs and a round pin for grounding. The ground pin is longer than the hot and neutral pins so that a ground connection is made before the connection to the voltage. The hot and neutral pins measure 1.5 mm thick, 15.9-18.3 mm long, and 6.3 mm wide. The ground pin has a diameter of 4.8 mm and is 3.22 mm longer than the two flat pins.

Type B electrical plugs have a current and voltage rating of 15A and 125V, respectively. They are widely used in North America, Mexico, China, Japan, and other countries which use Type A plugs. Like Type A, Type B plugs used in Japan vary in design slightly than those used in the United States.

CEE 7 Standard AC Plugs (Type C, E, F)

CEE Publication 7 is the “Specification for plugs and socket-outlets for domestic and similar uses .”This standard is maintained by the IECEE and governs the domestic electrical connectors used in Europe. The countries that do not use CEE 7 plugs and sockets as their primary power connectors are the United Kingdom, Ireland, Malta, Cyprus, Switzerland, and Italy.

Type C (CEE 7/16 and CEE 7/17) Plugs

Type C is the most internationally used electrical plug. It is an ungrounded and unpolarized plug and consists of two round pins. There are two types of Type C plugs:

• Europlug (CEE 7/16). Europlugs have two pins measuring 19 mm long and 4 mm in diameter. The pins are 18.6 mm apart from the base and 17.5 mm from the tip. They have an insulated covering 10 mm of their length from the base. The pins are relatively flexible, which allows them to fit in sockets that support rounded pins from 4.0 to 4.8 mm in diameter and whose slots are 17.5-19 mm apart. Europlugs are rated with 2.5A; the low current rating limits the Europlug to low energy applications.

  Europlugs are the more popular type of Type C plugs.

  
  

• Contour Plug (CEE 7/17). Contour plugs have two pins measuring 19 mm long and 4.8 mm in diameter. The pins are spaced 10 mm apart. Unlike Europlugs, contour plugs do not have an insulated sleeve. The insulated sleeve in electrical plugs makes their operation safer.

  Contour plugs are rated at either 10A or 16A; thus, they can be used in high energy appliances.

  
  

Type E (CEE 7/5) Electrical Plugs

Type E electrical plugs consist of two round pins, measuring 19 mm long, 4.8 mm in diameter, and 19 mm apart. It has a female contact or hole that accommodates the socket's earthing pin measuring 14 mm long and 4.8 mm in diameter. This contact is located beneath the plug pins. The asymmetrical arrangement of the pins in Type E plugs does not allow polarity reversal.

Type E plugs have a current rating of 16A. They are compatible with Types E and F sockets. These plugs are also known as “French plugs” and are widely used in France, Belgium, Slovakia, and Tunisia.

Type F (CEE 7/4) Plugs

Type F electrical plugs have almost the exact pin dimensions as Type E plugs, except the pins are not perfectly rounded. Type F plugs have two earthing clips instead of female earthing contact. These clips are located on the upper and lower sides of the plug housing, which is 16 mm from the midpoint of the imaginary line connecting the pins. These plugs also have a pair of plastic notches on the left and right sides to provide additional stability when used as a large built-in plug.

Type F plugs also have a current rating of 16A. They are not compatible with Type E sockets. These plugs are also known as “Schuko plugs” and are widely used in Germany, Austria, the Netherlands, and Spain.

CEE 7/7 Plugs

CEE 7/7 plug is a hybrid version of Type E and F plugs to fit both socket types. This plug has a female earthing contact to accept the grounding pin of the Type E socket and two earthing clips at the plug housing that works with Type F sockets. CEE 7/7 plugs are commonly found in countries that use Type E and Type F plugs.

British Standard Plugs (Type D, M, G)

BS 1363 is a British standard that specifies the safety, construction, electrical and mechanical testing, dimensional accuracy, and marking requirements for the plug and socket systems in the UK. Other countries such as India, Malta, and South Africa have also adopted this standard.

Type D (BS 546) Plugs

Type D electrical plugs consist of three round pins that form a triangular arrangement. The central earthing pin is 20.6 mm long and 7.06 mm in diameter, while the hot and neutral pins are 14.9 mm long, 5.08 mm in diameter, and spaced 19.1 mm apart. The asymmetrical arrangement of the pins in Type D plugs protects it from polarity reversal. Type plugs are rated at 5A. Type D plugs are widely used in India, Sri Lanka, Namibia, and Nepal.

Type M (BS 546) Plugs

Type M electrical plugs have the same arrangement as Type D plugs and are also protected from polarity reversal. They are distinguished from Type D plugs by their larger pins and current rating of 15A. The central earthing pin is 28.89 mm long and 8.71 mm in diameter, while the hot and neutral pins are both 18.94 mm long, 7.06 mm in diameter, and spaced 25.4 mm apart. Due to their larger current rating, these plugs are used alongside type D plugs in running appliances with large power requirements. Type M plugs are used in South Africa, Swaziland, Lesotho, the UK, Israel, and UAE. The South African variation of this type features an insulated sleeve and a bare connector on both pins.

Type G (BS 1363) Electrical Plugs

Type G electrical plugs consist of three rectangular pins that form a triangular arrangement and an incorporated fuse. The central earthing pin measures 4 mm by 8 mm by 22.7 mm. The hot and neutral pins are 4 mm by 6.35 mm by 17.7 mm long, and their center-to-center distance is 22.2 mm. The hot and neutral pins have an insulated sleeve covering half their length, while the earthing pin is uninsulated. British sockets have shutters that prevent foreign objects on hot and neutral pins.

Type G plugs include a fuse rated at 3A or 13A. The higher current rating is used in heavier-duty appliances. Hence, the Type G plug and socket system is considered the safest for both the user and equipment. However, Type G plugs are exclusive for Type G sockets and are not compatible with other types.

Type G plugs are also known as the “Commonwealth Plug .” They are widely used in the UK, Ireland, Hong Kong, Singapore, Cyprus, and Malta.

Type H (SI-32) Plug

Type H electrical plugs consist of three round pins arranged in a triangular configuration, with a diameter of 4.5 mm and a length of 19 mm. The center-to-center distance between the hot and neutral pins is 19 mm. The center of the earthing pin is 9.5 mm away from the midpoint of the imaginary line connecting the hot and neutral pins. Type H plugs are grounded and rated at 16A.

Type H plugs are only compatible with Type H sockets. Type H sockets are compatible with Type C plugs but are unsafe with Type E and Type F plugs. Type H plugs do not have an insulated sleeve, making them hazardous when partially unplugged.

Type H plugs are exclusively used and only found in Israel and Palestine.

Type I (AS 3112) Electrical Plug

Type I electrical plugs consist of two flat pins rotated 300 from the vertical, forming an inverted-V arrangement and a flat earthing pin. The hot and neutral pins measure 17.3 mm long, 6.3 mm wide, and spaced 13.7 mm. The pins are insulated. The earthing pin measures 20 mm long and is away from the middle of the plug by 10.3 mm. The width of the earthing pin depends on the current rating. For Type I plugs rated at 10A and 15A, the width is 6.3 mm and 8 mm, respectively. 20-A Type I plugs also exist with wider prongs. A lower current rating plug can fit a socket with a higher rating. Ungrounded Type I plugs also exist.

Type I plugs are mainly used in Argentina, Australia, New Zealand, Papua New Guinea, China, and other Pacific Island countries. In Type I plugs used in China, the earthing pin is above the other two pins, and all pins are 1 mm longer than the conventional. Type I plugs in Australia can mate with Type I sockets installed in China.

Type I plugs are documented in AS/NZS 3112, the harmonized Australian and New Zealand standard for plug and socket systems.

Type J (SN 441011) Electrical Plugs

Type J electrical plugs consist of three round pins whose dimensions are almost the same as Type C plugs. The hot and neutral pins are spaced 19 mm apart. The center of the earthing pin is 5 mm offset from the midpoint of the imaginary line connecting the hot and neutral pins. All pins have the same lengths and diameters of 19 mm and 4 mm, respectively. All pins are also insulated. The design of Type J plugs prevents polarity reversal. These plugs are rated at 10A.

Type J plugs look similar to the Brazilian Type N plugs. However, they do not fit into Type N sockets since their earthing pins are farther from the imaginary centerline.

Type J plugs are used in Switzerland and Liechtenstein. This type is listed in SEV 1011, the Swiss standard for domestic plug and socket systems, as the Type 13 plug.

Type K (DS 60884-2-D1) Plugs

Type K electrical plugs consist of two round pins and a U-shaped earthing pin. The hot and neutral pins have 4.8 mm diameter, 19 mm length, and 19 mm center-to-center distance. The U-shaped earthing pin has a 6.5 mm diameter, 14 mm length, and 4 mm thickness. These plugs resemble Type E plugs except for the gender and shape of the earthing contact. The design of Type K plugs disables polarity reversal. These plugs are rated at 16A.

Type K plugs are used in Denmark and Greenland. This type is specified under DS-60884-2-D1, the Danish Standard for plugs and socket-outlets for household and similar purposes.

Type L (CEI 23-16-VII) Electrical Plug

Type L electrical plugs consist of three round pins placed in a straight line. The earthing pin is positioned between the other pins. These plugs come in two variants which vary in the current rating and dimensions:

• The 10A variant has pins measuring 4 mm in diameter and 19 mm long. The centers of the hot and neutral pins are spaced 19 mm apart, while the distance of the center of the earthing pin to the center of the hot or neutral pin is 9.5 mm.
• The 16A variant has pins measuring 5 mm in diameter and 19 mm long. The centers of the hot and neutral pins are spaced 26 mm apart, while the distance of the center of the earthing pin to the center of the hot or neutral pin is 13 mm.

The 10A plugs are incompatible with the 16A sockets and vice versa since both variants differ in dimensions. The design of Type L plugs is symmetrical, which allows them to be inserted in any orientation. Thus, these plugs are unpolarized.

Type L plugs are used in Italy, Chile, Uruguay, and some countries of North Africa.

Type N (IEC 60906-1) Electrical Plugs

Type N electrical plugs consist of three round pins arranged in a triangular configuration. This type has three variants rated at 10A, 16A, and 20A. The pins of all variants are 19 mm long. However, the diameters are 4 mm, 4.5 mm, and 4.8 mm for the 10A, 16A, and 20A versions, respectively. The pins are covered with an insulated sleeve measuring 10 mm of their length. The center-to-center distance of the hot and neutral pins is 19 mm apart. The center of the earthing pin measures 3 mm away from the midpoint of the imaginary line connecting the hot and neutral pins. Hence, Type N plugs are not compatible with Type J plugs because this measurement is smaller compared to the latter (5mm).

The 10A and 20A Type N plugs are used in Brazil, while the 16A version is used in South Africa.

Type O (TIS 166-2549) Electrical Plugs

Type O electrical plugs consist of three round pins measuring 4.8 mm in diameter. The hot and neutral pins measure 19 mm long and have an insulated sleeve covering 10 mm of their length. The earthing pin is 21.4 mm long. The center-to-center distance between the hot and neutral pins is 19 mm. The earthing pin is 11.89 mm offset from the center of the imaginary line connecting the hot and neutral pins. Type O plugs are rated at 16A.

Type O plugs are exclusively used in Thailand, and this type is described in TIS 166-2549. The Type O plug and socket system was introduced in 2006 and is currently being phased in.

Chapter 4: Plug Adapters and Replacement Plugs

Plug Adapters

Plug adapters are small devices that make it possible to insert a plug into a receptacle with a different number of prongs or shapes. They are used to insert a plug into an incompatible type of receptacle, and this instance is frequently encountered when you visit a different country. However, they are not designed to convert voltages and current. Plug adapters are also known as power adapters, travel adapters, and ground plug adapters.

Cheater plugs, or three-to-two prong plug adapters, can allow a three-pronged plug to a two-slot receptacle. They run your electrical appliance normally, but they disable the grounding feature of the three-pronged receptacles. Therefore, these adapter plugs must not be used for a long time and be operated with extra precaution.

Replacement Plugs

Replacement plugs are used to replace worn-out or damaged plugs of an electrical cord. They consist of terminals for the hot, neutral, and grounding terminals contained in a plastic housing. No appliances or cords are attached at the end of these devices.

The replacement plug must be of the same type and rating as the original cord. The electrical cord must be unplugged from the outlet before installing the replacement plug. The old plug is cut from the cord, and the outer jacket and wire insulations are stripped to expose the wires. The bare wires are then connected to the corresponding terminals in the dismantled replacement plug. Finally, the wires are locked in place, and the housing is reassembled.

Conclusion

• Electrical plugs are devices responsible for supplying current from the receptacle to the circuity of an electrical appliance.
• Electrical plugs have two or three prongs. Hot and neutral pins are present in both two- and three-pronged plugs. A grounding pin is introduced in three-pronged plugs as a safety feature.
• There are fifteen standard types of mains electrical plugs recognized by the International Electrotechnical Commission (IEC) and listed under the IEC-60083 standard. Each type has a letter designation. These types differ in the dimensions, the number of contacts, current and voltage ratings, and the countries in which they are used.
• Plug adapters enable the insertion of a plug into an incompatible socket.
• Replacement plugs are devices that replace worn-out or damaged plugs of an electrical cord.

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