A circuit needs a complete path.
A simple circuit has a source, conductors and a load connected in a loop. The load converts electrical energy into another form: a lamp produces light and heat; a motor produces motion and heat.
An open circuit has a break in the path. A closed circuit has a continuous path. Current is not consumed by the load; energy is transferred.
Try the switch.
Switch open: the path is broken and the lamp is off.
Series and parallel arrangements.
In a series circuit, components share one path and the same current flows through each. Their voltage drops add up to the source voltage.
In a parallel arrangement, branches connect across the same two points. Each branch has the same voltage, while the supply current is the sum of the branch currents.
Switching power and signalling a condition.
A lift switch may operate a load directly or provide information to a controller. A button press is often a request that the controller evaluates before allowing movement.
Opening one circuit is not proof that a complete lift installation is isolated. Here we are explaining circuit behaviour, not a procedure for working on equipment.
A closer look
A short circuit is an unintended low-impedance path. It is different from an open circuit and may allow a very large current. Protective devices address fault conditions; they are not substitutes for correctly designed circuits.
Check your understanding
Two lamps are on separate parallel branches. Does one open branch necessarily turn both lamps off?
Reveal the explanation
No. In this ideal example, the other complete branch can still carry current. A break in their shared supply would affect both.