# How the power grid is able to work even when some circuits are not closed

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As far as I’m aware, for electricity to flow, a circuit has to be closed. How is it that if I flip off a light the entire city’w power doesn’t go down. How does the power grid isolate circuits while still allowing a circuit to be closed?

In: Engineering

There is still a complete circuit being formed. It is just not sending power to the thing connected to the switch. It is just sending it back.

The circuits are connected in parallel. If you cut off one of the circuits, the others are still connected.

Consider [this diagram](http://www.technologystudent.com/images5/prcirc2.gif). If you remove one of the bulbs it only cuts off that circuit, but electricity can still flow through the other bulbs.

Imagine you have a loop if wire connected to a battery. You want to use this battery to power multiple things in multiple areas. You have more wire available as well, and all the tools and items you need to hook everything up.

So let’s start by attaching one light bulb with a power switch to the grid. We will start with the power switch. First what we do is strip a small section of insulation from off the wire in two nearby spots. Next we take one wire and wrap it around the exposed to section of the main wire. We take the other end and connect it to the switch we can take another wire connecting the switch to the light bulb, and finally a final wire going from the light bulb back to the main wire.

When the switch is closed power will flow threw it to the light bulb and back into the main loop, but when it is open power will simply continue along the main loop.

Likewise you can add secondary loops onto the main loop, and even attach switches called breakers which are made to shut off in the event of an electrical issue. This way you can disable all the power in one small area without interfering with the entire system.

And you can do loops on loops on loops each with their own breakers switches etc to create smaller parts of this electrical system.

This is a scaled-down version of what the gist of the electrical grid is. You have a large major loop upon which smaller neighborhood loops are attached, upon which individual houses are wired, upon which individual circuits are wired. Turning off your light switch does not affect the power across town because at the points where power enters a smaller system it is still capable of continuing along if that system is left open.

I would look on Wiki for the difference between parallel and series circuits. It would be weird if everything was wired in series, meaning every light switch in the city, every outlet, every single thing needed to be on for anything whatsoever to be on.