Just Out of Curiosity

Yes, LongintheTooth has it.

And 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 according to:

Why do the two flat prongs on the plugs for electrical appliances

Thanks, Lyn. Never considered the lockout angle, thats new. Thanks again.

I never considered the retention angle.

Thank you.

adding a thought....back in the old days of auto ignitions with "points", points morphed over time and referred to as "ventilated points". one of the contact points had a hole in. when the points arced during normal actuation this vent lessened micro-welding of the points. its possible the plugs are also incorporating a vent hole to prevent the sane when the plug is removed under load and arcing often occurs momentarily

The're to clean the contact surface....

At one time all plugs had the holes in the blades because the primary point of contact was a dimple in the socket. The hole is a hold over from old times.

Good Luck, Old Salt

Yes, you can recognise cheap electrical devices by the fact that they do not have the holes. The loss of retention is readily observed on the low cost plugs. Larger plug / socket combinations do not have the holes because the area and tension of the contact spring is larger. The increased holding power of the later addition of a grounding pin almost eliminated the need for the holes, but its nice they are still there in the event the ground pin goes missing. ( talking about north american connectors here ). The same blades are used in 2 and 3 wire connectors, so its easier to put holes in them all.

All good explanations. Thanks.

So they are not there to hook conductors through if your extension cord is missing the correct receptacle. (which motivated my question in the first place)

Scary thought, but it is technically feasible using lugs and small hardware. Can't think of a situation where it would be attempted other than a homeowner on his own responsibility. I would think seeing that in a job site would be immediate discpilinary action.

My parents' house (built in the 20's) has two-prong receptacles that utilize a neat little 1/8th turn locking action. The holes in the plugs are used by those receptacles. I always assumed it was to stop the plugs from being yanked out.

I'll have to ask my dad if the recp's are still there, part number, etc.