Why are there holes in the blades of electrical plugs?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As shown above, both the flat blades on an electrical plug like the NEMA 5 shown above have holes in them. What are they for? There are multiple, plausible-sounding stories -  but they just aren’t true. Be careful to check them out before using one in a speech.

 

So the socket can grip the plug

 

 

 

 

 

 

 

 

 

 

 

 

 

As shown above via a cross-section, this might be to engage with a locking ball or other device. An article at howstuffworks on January 3, 2022 titled Why do electrical prongs have holes in them? claims:

 

“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 socket.”

 

Unfortunately a 20-minute YouTube video at Technology Connections titled Holey Plugs, Batman! But … what are they for? thoroughly debunks that claim.    

 

 

Safety lockout

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A second more likely claim at howstuffworks (as shown above) is:

 

“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 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.”

 

On February 18, 2011 I blogged about More on mistake-proofing: lock out what you don’t want to happen.

 

 

Saving material (and money)

 

 

 

 

 

 

 

 

 

 

 

 

 

A third claim at howstuffworks is:

 

"There also is a small savings in raw materials (metal) for the manufacturer of the actual plug prong. Every little bit helps!"

 

But based on the exposed length of a blade and the hole diameter, the savings in metal volume is only five percent. Why wouldn’t there be a second hole to raise that to ten percent?

 

 

What are the holes really for?

 

 

The YouTube video at Technology Connections titled Holey Plugs, Batman! But … what are they for? explains at 12:15 that the holes just allow alignment of the blades during the manufacturing process (molding the plug around the blades).

 

An image with stacks of $100 bills is from Wikimedia Commons.