The switch on the left of the faceplate is a 10 amp switch that can be used for lighting, fans, heaters or any application where a switch was needed.
These outlets were common in bedrooms where only one power outlet was needed, saved running extra wire down the wall. You used a mixed (light/power) circuit and took the active from the terminal on the back to the switch & then run the switch wire (controlled by the switch on the left) back to the light.
I seem to recall seeing a more modern version of this idea in a Jaycar catalog some years back: Dual general-purpose outlet each with its own switch, plus a third switch centrally mounted. It had the little round rocker switches -- Like some of the Clipsal range here.
Similar to this type but with third switch top center:
Last edited by pauluk; 05/26/0708:44 AM. Reason: Added image
Darren, It's interesting that sockets had safety shutters in them back then. It's my guess that the shutters operated the interlock on the switch.
Here's an HPM horizontal double socket outlet with extra switch:
Popular here in kitchens where the switch is often used to power a socket outlet supplying either a dishwasher or waste disposal unit. They are also used in bathrooms for shaver sockets and the switch used for vanity unit lighting.
Last edited by Trumpy; 05/26/0704:28 PM. Reason: To add image