# [ELI5] What does it mean to be “grounded” against electricity, and why does it keep you safe?

21 views

[ELI5] What does it mean to be “grounded” against electricity, and why does it keep you safe?

In: 66

Electricity wants to ground out, literally go into the ground. “Grounding” a circuit gives it a path to do so that doesn’t involve ripping through you and blowing off your toenails.

“Ground” is a sometimes misleading term. It can mean “earth ground”, or the electrical potential of the literal ground under our feet. It can also mean “the negative terminal of this circuit”, which may or may not be at or near the same potential as earth ground.

One (very limited and kind of poor, but works for this) analogy might be to think of it as water in multiple tanks. If the water level in the “earth” tank is low, and you connect it to another tank, whose level is higher, then water flows from the tank with the higher level to the “earth” tank. But if the “earth” tank is at or close to the level of the other one, little or no water flows.

To be truly “safe” from electrical shock, you need to never be part of the path that current wants to take- or, to reference the above example, you don’t want to be the pipe between the tanks.

Actually being grounded- meaning, your body is at the same potential as earth and there’s a conductive path through you to earth- might actually make you *less* safe, because electricity could travel through your body.

Electricity wants to reach the ground to dissipate, and to do so it wants to find the path of least resistance. It’s a lot easier for electricity to pass through your body than air, so if your feet touch the ground and your hand touches a circuit, the path of least resistance is through your body. Grounding yourself is providing an alternate path that’s preferable for the electric current that does not go through your body.

There is two facts that we have to establish here first in terms of safety around electricity.

1. Electricity hurts you when it flows through you.
2. Electricity prefers to flow through path with least resistance. Like water, if one pipe is small and the other is big, water would flow more through the bigger pipe. In other words, electricity is lazy.

Now, according to fact 1, if there is little to no electricity flows through you, then you’re fine.

According to fact 2, electricity doesn’t flow if you have significantly higher resistance than other path.

So, usually, what we do is:

1. We provide a superbly easy way for “rogue” electricity to flow. This is usually accomplished by having the machine “grounded” (having an almost direct connection to literal ground)
2. We make ourselves as resistant as possible, via rubber-gloves and shoes, usually.

You as a person being grounded (at the same potential as the neutral wire coming into your house) is bad. If you touch one of the hot wires coming and are grounded, current will flow from the hot wire, through you, to the ground because the neutral wire is at ground potential.

A safety ground (or chassis ground) is important for devices with a conductive outer chassis (most appliances for example). Let’s say your metal toaster has a frayed hot-wire inside it. This wire touches the metal chassis of the toaster. It is now at the same potential as the hot wire. When no one is touching it it’s a open circuit, no current flow. But you come in to the kitchen and touch it while your feet are on the floor, you have created a full circuit and current will flow. Ouch

Now a number of factors come into play that determine how much current will flow. If you are on the 2nd floor of your house wearing rubber boots and your hand is dry, you might only feel a tingle because your insulated from ground potential. If you just got out of the shower and are barefoot on the basement floor, you might have a worse day.

This is where a safety ground comes into play. The safety ground is wired up to a grounding rod buried into the ground, usually where your electrical meter is. This is wired to the chassis of your metal toaster, so that when the hot wire in the toaster touches the chassis, it creates the circuit instead of you. Also this will act like a short circuit and immediately trip your circuit breaker.

“You” don’t want to be grounded, you don’t want to be apart of the circuit at all. What you want is something more conductive then you near or around you to divert the current away from you. You want to be the hardest thing for electrons to pass though in your yard when lighting strikes.

Electricity does not have a tendency to flow to ground. That is a common misunderstanding.

However, when a piece of electrical equipment is connected to the earth (via a metal rod in the actual ground), it is commonly considered “earthed” or “grounded”.

The reason is for safety of electrical shock. Electricity flows in a loop. It must complete a circuit back to where it came from,and it takes all possible paths. However, it prefers the easiest path.

So under normal circumstances, power is generated at the power plant, goes down the power line to your house, to the equipment, then back down the wire and power lines back to the power plant.

Now imagine what happens if you have two pieces of electrical equipment. In one, the incoming wire comes loose and touches the case. In the other, the return wire comes loose and touches the case. You then walk past and touch both cases, you now complete the circuit and get shocked.

To protect against this type of problem, metal equipment cases must be connected to a common point, so that if you touch two pieces of equipment at the same time, you don’t get a shock. Most power flows through the wire connecting them togetger, instead of you.

Because you are standing on the ground or washing with water in metal pipes in the ground, then it makes sense that the safety bond is also bonded to ground. So, that there is already an easier route for power than through you.

Finally, because you don’t want loose wires to go unnoticed, you need some way of detecting faults. This is easier if the power plant is also connected to ground. This way the ground itself completes a circuit of a wire comes loose and lands on the ground (or touches the case of equipment). There can then be fault detection systems in your home which detect this power flow to ground and cut off the power.

Good explanations. Just to add to it, if you read an owners manual for a power tool (electric power tool), it says when you are using it make sure you’re not touching a ground. For example, if you are using a drill or saw in your house, don’t lean or touch a radiator as an example. Just something to be aware of.

Grounding is used to protect things from being damaged by electricity. This is done by giving the electricity a safe path to follow to Ground. We call it ground because the sticking a metal stick in the ground is a great place for the electricity to go.

Ground straps and ground wires are two types of these safe paths.

1. Ground wires protect you from electricity in a machine.
2. Ground straps protect machines, from (static) electricity in you.

It is *not* as simple as Grounded=Safe. Using the wrong type of ground could be deadly.

You are creating a path for electricity to flow through, but it is not a safe path it is your body.

In fact, many electricians wear insulated boots when working, these boot help prevent your feet from making a path to the ground from electricity.

Grounding is used to protect things from being damaged by electricity. This is done by giving the electricity a safe path to follow to “Ground”. We call it ground because on best paths is into the ground. Most houses have a big metal stick deep in the ground with a ground wire attached.

Ground straps and ground wires are two types of these safe paths.

1. Ground wires protect you from electricity in a machine.
2. Ground straps protect machines, from (static) electricity in you.

It is *not* as simple as Grounded=Safe. Using the wrong type of ground could be deadly.

You are creating a path for electricity to flow through, but it is not a safe path it is your body.

In fact, many electricians wear insulated boots when working, these boot help prevent your feet from making a path to the ground from electricity.

Basically, electricity is lazy. It will follow the easiest route (that is, the route with the least resistance). Grounding gives it a nice easy route somewhere safe where it can dissipate and be no harm to you.

Whenever you have two things with different electric charges, electricity will flow between them. This flow is what makes electricity dangerous, and is governed by two things:

1. How large is the difference between the two charges? (Voltage)
2. How easy is it for the electricity to flow? (Resistance)

If the charge is the _same_ between two things, then no electricity will flow. If it’s too difficult for the electricity to flow quickly, then even if there is a large difference, it won’t flow very fast.

“Ground” typically refers to the thing in any particular electrical system that has the least amount of charge, but it is entirely arbitrary. For a thing to be “grounded” simply means that it is connected to the thing that is “ground” such that both things always have the same charge.

In a home electrical system, the “ground” thing is _literally the ground/earth_. This means that as long as you have the same charge as the earth/house, nothing grounded to the house will ever shock you. Appliances with a grounded plug use the ground connector to connect their outer shells to the home’s ground, which prevents you from being shocked by the outer shell of the appliance.

Ground connectors are also important because when there _is_ a difference in electrical charge between two things, they provide an easy path for the charge to equalize that isn’t you. Humans have a very high resistance, so electricity will flow through other things like a ground connector if it is available instead of you.

Rubber gloves and other insulating protective wear helps when you come in contact with a non-grounded thing by greatly increasing the resistance, thus slowing down the electricity enough that it won’t harm you.