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Two Prongs or Three? Grounding Explained

You probably already know not to cut off the third prong of an electrical plug in order to fit it into a two-prong electrical outlet. If you didn't already know, you do now. But why is this dangerous and, if it is, why do some outlets only have two prongs in the first place? Read to find out.

The Basics of a Home Electrical Circuit

Electricity needs to flow in a circuit. That means that at the very minimum, your power outlet is going to need two prong sockets – electrical current from the hot socket flows towards the neutral sockets, powering washing machines and toasters on its way. So far so good.

So what would happen if you placed a metal wire in the hot socket and connected it directly to the neutral socket? A huge amount of electricity would flow completely unimpeded, possibly starting a fire and definitely electrocuting you in the process. When this happens in an electrical device, it's called a short circuit.

This doesn't happen with electrical devices because they are built to limit the flow of electricity. For instance, a light bulb works by cutting the flow from hot to neutral to only 60 watts. The third prong only comes into play when your appliance is enclosed in a metal case.

Metal Cases Conduct Electricity

What happens to you if the interior wiring of a metal-enclosed device comes loose? If the hot wire touches the inside of the metal case, it will electrify the case and fatally shock you the second you touch it. However, if that metal case is connected to a third wire that leads back to the breaker box, the electricity will not flow through you, but through the circuit, tripping the circuit breaker in the process.

As you can see, if you saw off the grounding prong on a three-prong cable and plug it into a two-prong outlet, there is nothing protecting you from shock if interior wiring comes loose. Since grounded devices tend to be larger power draws than ungrounded devices, this is a serious danger – you never know when a small wire might accidentally create a short circuit inside the device.

Obviously, confusing any of these wires is also extremely dangerous. For this reason, wires are color-coded. Hot wires are wrapped in black plastic insulation, neutral wires in white insulation, and ground wires are bare. In ungrounded appliances, the wires are typically doubly insulated against any possible interaction with metal components.


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