What do these symbols in ac connectors stand for?

Question

I'm trying to use a relay to control my house lights with a electronic circuit. I'm familiar with 5V DC circuits, but I've never played with AC before. My relay has three connections, which I assume are ground and the two wires that will be connected when the thing is on.

However, I can't find any datasheet or information about it, my only clue are these symbols:

Using pure logic I would guess that the "bottom" (in the picture) and the middle one are the connectors, and that the other ("top" one) is the ground. So when it is on the relay connects bottom to middle, and when it is off, connects the top to middle. Is that it?

And one more thing: my house is not grounded (yeah...). So is it safe to not connect anything in the ground terminal (leave it unplugged), or for this specific case I'll have to use some quirk to make it work?

Answer 1

By convention, relay contacts are shown in the de-energized state.

The middle is the common. Top is normally open (connected to common when energized). Bottom is normally closed (connected to common when de-energized).

Verify with a multimeter.

The blue relay is a Sanyou type, very common and somewhat nasty pinout.

Not enough information (nor desire) to speculate on residential wiring codes and permissible connections in Brazil.

Answer 2

It's a either a switch contact or an internal relay contact. The middle pin is the switch pole and the upper pin is the normally-open contact.