# How Electrical Current Flows

Here is a simple analogy comparing flow of electricity to the flow of water that should help you to understand how electricity is measured.

The main electricity units that often are quoted are Amperes, Volts and watts. If you can imagine electricity flowing through a conductor like water through a hose, here are your comparisons.

Amps describe the diameter of the hose. A house with 200 amp service can power a lot more loads than one with 100 amp service. A 15 amp circuit for lighting would not be sufficient to power a clothes dryer which usually would need 30 amps.

Voltage is the pressure. In North America, standard household service is 120 volts. It is power waiting to be drawn. Like the water pressure behind a faucet. Have you ever notice the lights flicker when you turn on a vacuum, or the shower pressure drop when you flush the toilet, same thing.

Watts is the volume of water that you draw through the hose, and this is what you get billed for. A 100 watt bulb refers to the amount of electricity it needs to stay lit. You pay for kilowatt hours which is 1000w of power draw for 1 hour, or 100 watts for 10 hours.

The relationship between the 3 is mathematical one. At 120 volts, a 15 amp circuit can handle 120 x 15 = 1800 Watts of continuous load. Conversely, a 60 watt bulb operating on a 120 volt circuit is said to be drawing 60 / 120 = 0.5 Amps

There is another common parameter and that is ohms, or resistance. This would be leaks in the hose over distance. So pressure applied at the start of the hose could be 120 V, over a mile long hose there may be a voltage drop due to leaks in the hose or friction causing heat, this could be described as ohms.

When you have a Direct Current or DC circuit, the flow is in one direction. Imagine a battery with 2 poles, one positive and one negative. Imagine one as a faucet and the other as a drain. All that is needed to commence the flow is a device to close the circuit. If you place a light between the poles, the electrons will flow through the bulb and through the filament which will illuminate, and then will pass to the drain. Eventually the battery will be depleted.

When you have an alternating current or AC circuit. The flow “vibrates” in both directions in a fixed interval or frequency. Household current is typically AC. In the light bulb example, the electricity flows though the bulb in both directions in an alternating fashion, giving you light.