Homeowner’s Guide to Electrical Grounding and How It Works
You know electrical grounding is important. What does it actually do?
Whether you’re an experienced DIYer or just getting started, electrical grounding is one of the most important — and confusing — concepts to grasp.
Maybe you’ve heard of grounding, but aren’t sure exactly what it does. Maybe you’ve seen, and even connected, the green “ground wire” in a DIY electrical project. Or maybe grounding a completely new concept to you, and you’re looking for a simple explanation.
Here, I’ll tell you what electrical grounding is, what it does, and why it’s so important for the safety of every electrical circuit in your home.
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What Is Electrical Grounding?
Grounding means connecting to the Earth, or extending the ground connection to other things in your home — even if they’re far away from the actual ground. Establishing a connection to the Earth has several safety and logistical benefits, and it’s been required in some form by the National Electric Code (NEC) since the earliest days of electricity.
Before we go any further, let’s review how electricity is delivered throughout your home.
How Does Electricity Work?
When you walk into a room and flip on a light switch, electricity in the form of current flows through the switch to the light. This electrical current is made up of electrons, tiny subatomic particles that are constantly on the move.
It’s these electrons that cause your light to go on, as well as your toaster to toast and your washing machine to run. Until you flip the switch off, these electrons keep cycling from your electrical panel to the light and back again, in a continuous loop called a circuit.
Current keeps circling the loop because of a fundamental truth about electricity: It always wants to return to its source, which in your home is the electrical panel.
Copper or aluminum wires, called conductors, carry the current from your panel to everything in your home that needs power, and back again. These metals are used because they’re conductive, meaning electrons easily travel through them. Voltage is the force that pushes the current through the circuit.
The Earth is also a conductor. And you can be one too, unfortunately. Electrical current is opportunistic, and it will take whatever path it can to return to where it came from. If you get in its way — aka become part of the circuit — the current could decide to go right through your body. It only takes a tiny amount of current to kill a person.
Why Do We Ground?
In a word: Safety. If the current powering our lights, appliances and tools could kill us, it’s important to mitigate that danger, right? Grounding is how we accomplish that, and there are two ways we do it:
Your house wiring is an electrical system, connected to ground at your electrical panel. Tools, appliances, lights and electronics need specific voltages to operate correctly and safely, and system grounding stabilizes these voltages.
Grounding ensures that wherever you plug in your computer or television, you’ll get the same 120-volt circuit (plus or minus a few volts). Every time you dry your clothes, your electric dryer gets 240 volts to operate safely. System grounding also limits voltage surges if lightning strikes your home or the surrounding area.
Equipment grounding and bonding
When you think of electrical equipment, you probably think of appliances and tools — things you plug in and use. You’re right.
But with grounding, the term also includes appliance frames, junction boxes, conduit (pipes) and other metal things that don’t normally carry, or use, electricity. These “non-current carrying” metal parts must be grounded (connected to the Earth) in case they become energized.
Take your washing machine. If one of the conductors (wires) delivering electricity to your washer becomes loose or frayed due to age or friction, it could accidentally come into contact with the metal frame, electrifying it. If that happens, your home has a circuit breaker that shuts off the circuit.
How does the circuit breaker know to trip? That’s where bonding comes in.
Bonding means connecting to establish electrical continuity. When the frayed wire hits the washing machine, it creates a ground fault. This unintentional, really high current needs to return to the panel and the circuit breaker, fast. It can’t travel on the regular pathway (the circuit conductors) because the washing machine frame interrupted that path. It must take an alternate route. Electricians deliberately install a route for this purpose.
The route can be an appropriately sized green or bare wire, or the metal parts themselves, but it must be continuous all the way back to the panel. Without this path, the frame could sit energized, waiting to shock a person or pet. Equipment grounding and bonding mitigate the danger from electric shock.
How Does Electrical Grounding Work?
So we know grounding is important, but how does it work? Why does connecting to ground make things safer? This can be confusing, but stay with me.
When you were a child, did you ever walk across carpet in your socks, then touch your friend to give them a shock? (Maybe you still do this. No judgment.)
Your friend received a shock because you picked up a bunch of excess electrons from the carpeting, and your pal had a deficiency of electrons compared to you. The electrons sensed this relative difference, also called a potential, and moved to your friend to return to a state of equilibrium.
Electrons in electrical circuits behave similarly; they constantly move to a different potential. The Earth (ground) has a potential of zero, while your home’s electrical circuits have higher potentials — 120 volts and 240 volts higher. (That’s right, potential is the same as voltage.)
Remember earlier when I mentioned you could be a conductor? If you touch the electrified metal frame while standing on the zero-potential Earth, the electrons in the 120-volt circuit can sense that potential difference, just like when you zapped your buddy with static electricity. They could use you and the Earth to get back to their source. That’s bad.
Luckily, electrons will only go through you if they sense a difference in potential. Connecting the washing machine frame to ground, through the green wire or the bonded metal parts, keeps it at Earth potential (zero) so you can’t become part of the circuit.
If the frame ever becomes electrified, even for a split second, the current instantly goes back to the panel along this deliberately-installed path, instead of waiting for you to come along and complete the circuit.