This is the type of plug I’m referring to: [https://www.dhcsupplies.com/store/p/6483-9-x-16/3-Power-Supply-Cord-with-U-Ground-Plug.html](https://www.dhcsupplies.com/store/p/6483-9-x-16/3-Power-Supply-Cord-with-U-Ground-Plug.html)
In: Engineering
Polarity!
While for many applications (especially an incandescent light bulb) it doesnt matter which prong power goes in / comes out, sometimes it does. Especially electric motors, and having them all push/ pull in the same “direction” is more efficient for the electrical grid as a whole.
The holes have a couple of uses:
1st they allow for locking out/tamper proofing, along the line of a plastic tag with instructions like “you must do x,y,and z before plugging in.
2nd, they align with bumps in the socket that help keep the plug snugly secured and prevent accidental removal.
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