Why Do Electrical Plugs Have Holes

The Holes In The Electrical Plugs Are Used For Gripping

The holes you see in plugs are used for gripping the plugs inside sockets. Historically, sockets had bumps inside of them. These bumps were intended to fit into the holes. Without these bumps and holes, it would have been very easy to simply pull the plug out of the socket. 

Having these holes and bumps allowed some resistance without making it impossible to unplug. Modern designs have largely deprecated the bumps inside sockets and instead use other factors such as friction or even the use of rods to keep sockets in place.

Who Invented Them?

The invention of holes in prongs is credited to Harvey Hubbell Jr., an inventor who tried to find a way to make plugs gripping into sockets easier. His solution was adding small indents inside the prongs, which would then make contact with bumps inside sockets. Eventually, the indents would be replaced by holes, although the basic idea remained the same.

Why Do Electronic Plugs Have Them?

For these answers, there are 3 main reasons:

1. If you were to take apart an outlet and look at the contact wipers that the prongs slide into, you would find that they have bumps on them. These bumps fit into the holes so that the outlet can grip the plug's prongs more firmly. This detenting prevents the plug from slipping out of the socket due to the weight of the plug and cord. It also improves the contact between the plug and the outlet.
2. Electrical devices can be "factory-sealed" or "locked out" by the manufacturer or owner using a plastic tie or a small padlock that runs through one or both of the prong holes. Construction projects or industrial safety requirements may require this type of sealing. For example, a manufacturer might apply a plastic band through the hole and attach it to a tag that says, "You must do blah blah blah before plugging in this device." The user cannot plug in the device without removing the tag, so the user is sure to see the instructions.
3. There also is a small saving in raw materials (metal) for the manufacturer of the actual plug prong.

Types Of Hole Prong Plugs

1. 2 Prong Plug Holes

Named as Nema 1-15. when it was invented by Harvey Hubbell II, two-pronged plugs are now known as Type-A plugs. These types of ungrounded plugs are pretty common in North and Central America.

the two prongs have a 'hot' and 'neutral' side. The wider prong connects to the neutral wire and the smaller prong is the hot side of the circuit.

2. 3 Prong Plug Holes

Named as Grounding Receptacle. Unlike two-prong receptacles, three-prong receptacles are connected to a ground that protects the electrical appliance that is plugged into it from being damaged in case of a short circuit. If one of the prongs or the wires inside them becomes dislodged, electricity won't flow as efficiently through the device. This misdirected current could, at times, ruin appliances or may even shock the user because it is no longer grounded.

Why Do We Use Three-Prong Plugs?

A three-prong plug is designed so that electricity can be safely supplied to electrical appliances. The third prong grounds the electricity to protect anyone who uses the metal-encased appliance from electric shock.

Can You Cut The Third Prong Off?

Technically nothing happens if you cut the third prong off. However, you've disabled an important safety feature that protects you from electric shock if a wire comes loose.

What Wires Go On A Three-Prong Plug?

The left slot is "neutral" and the associated white wire should be connected to the silver screw. The right slot is "hot" and the associated black wire should be connected to the brass screw. The green "grounding" wire should be connected to the green screw.

Do All Electrical Plugs Have Holes?

Strictly speaking, holes are not necessary for electrical plugs. Plug holes are distinctive features of Type A and Type B plugs. These are mainly used in the United States, Canada, Japan, and a few other countries. This standard is also known as the NEMA standard. It is not uncommon for plugs of this standard to not have holes, although holes remain commonplace. The main difference between Type A and Type B plugs is that the latter has an extra pin, known as a ground pin.

Many other parts of the world, notably Europe, use narrow and circular prongs for their plugs. This plug version has many variants, such as the Type E standard commonly used in France, and the Type F standard (which is similar to Type E except the socket does not have a ground pin). As can be seen in the picture above, their prongs do not have holes in them. 

Some other plug standards, such as the Type G standard used in the UK and the Type I standard used in Australia, also use flat prongs like the Type A and B standards. However, the Type G standard uses thicker prongs and does not use holes. Type I plugs have flat prongs like Type A and Type B; plugs that use this standard sometimes have holes, but their presence is not universal.