Why Do Flat Electrical Plugs Have Two Round Holes? The Reason is Amazing.

11 September, 2024

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Have you ever noticed the flat power plug with two round holes in the metal prongs? What are these holes for?

Why does a flat power plug have two round holes?

The primary purpose of these holes is to provide a more secure and stable connection. Standard electrical outlets feature a raised portion that fits perfectly into the round holes, acting as a locking mechanism to keep the plug firmly in place and ensure a steady power supply.

Why Do Flat Power Plugs Have Two Round Holes?

The holes also serve a safety purpose, helping to prevent children from accidentally touching the electrical outlet and reducing the risk of electrical hazards. Some older outlet designs without holes may become loose over time, exposing the electrical contacts, which can be dangerous, especially in households with young children.

In the past, power plugs had indentations on the prongs, which created friction and sometimes sparked when inserted into the outlet. The switch to perforated prongs reduces this friction, minimizing the risk of electrical arcing and providing a safer experience for users.

Additionally, manufacturers now utilize these holes to attach seals or labels, enabling consumers to distinguish between genuine and counterfeit products.

The presence of these two holes also results in significant steel savings for manufacturers, especially when producing plugs in large quantities.

Manufacturers also use these holes to attach seals or labels, helping consumers identify genuine products.

The invention of these holes is credited to Harvey Hubbell Jr., who initially added small indentations inside the prongs of the power plug to make contact with the corresponding ridges inside the outlet. Over time, these indentations evolved into holes, maintaining the same basic principle.

Currently, there are mainly two types of flat power plugs with perforated prongs: Type-A, featuring two flat prongs, and Type-B, which has one flat prong and one round prong for grounding. These types are commonly used in countries such as the United States, Canada, Japan, and a few others. This standard is also known as the NEMA standard.

In contrast, round-prong power plugs are more prevalent in European and some Asian countries. The round design of the prongs and corresponding outlets provides sufficient grip, eliminating the need for perforated prongs in these regions.

Frequently asked questions

The two round holes on flat electrical plugs serve a specific purpose. They are designed to accept a type of fuse called a ‘ferrule fuse’, which is a small, round, glass tube with a metal cap on one end and a metal ferrule on the other. The fuse is inserted into the plug, with the metal cap fitting into one of the round holes and the ferrule fitting into the other. This type of fuse was commonly used in older electrical systems and appliances, and it served as a safety feature to protect against electrical overloads.

Ferrule fuses contain a thin wire that melts when exposed to excessive current, interrupting the electrical circuit and preventing a potential fire hazard. The metal cap and ferrule on the fuse create a secure connection with the plug, ensuring reliable electrical contact. This design not only provides safety but also allows for easy replacement of fuses when needed.

While ferrule fuses were once a standard feature in electrical plugs and appliances, they have largely been replaced by more modern fuse designs, such as the ceramic tube fuse or the blade-type fuse. However, you may still find older appliances or electrical systems that utilize ferrule fuses, especially in vintage or antique items.

If you own an older appliance or device that utilizes a flat electrical plug with ferrule fuses, it is important to handle it with care. Ensure that the fuses are in good condition and have not blown. If you need to replace a fuse, make sure to use the correct type and rating for your appliance. It is also advisable to consult a qualified electrician if you have any concerns or require assistance.