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I have always had the most difficult time understanding why I need both a neutral and ground wire when they ultimately both connect to the same bar in a breaker box. And I’m not alone. A lot of people struggle with this distinction. I’m hopeful that this guide, courtesy of research, will help to clarify it.
The neutral wire serves as a return path for electrical current while the ground wire provides a path for electrical current to earth. Since electricity flows from source to destination and back, each wire serves a specific need to ensure the loop is maintained.
As you will see, neutral and ground wires do have some similarities, but let’s debunk some myths and get a clear understanding of why each of these two wires is needed and how they differ.
Note: It’s recommended that you always seek the assistance of a licensed electrician when issues arise concerning electrical wiring. This article is based on research and sources are cited.
The Purpose of Ground Wires and Their Connection to Neutral
Electricity always flows in a circuit, meaning it must continue in a loop from its source, through an appliance, and back to the source. A completed circuit is necessary for electricity to flow—switches work by breaking this continuous circuit.
Outlets and appliances in America are standardized to work with the 3-wire system.
Typically, we think of it this way: A “hot” wire carries the effective voltage of 120 volts to the appliance through the outlet, while the “neutral” wire serves as the return path.
The third wire, called the “ground,” is connected to the metal case of the appliance and is connected, literally, to the ground (source).
A ground wire provides a conducting path to the earth. Under normal circumstances, electricity does not need to flow through this extra wire.
However, if a hot wire shorts, the voltage will be applied at a very low resistance through this “grounded” wire, thus tripping the circuit breaker and interrupting the circuit.
The purpose of the ground wire is to protect against shock hazards that can occur when an exposed hot wire comes in contact with a metal part of the appliance.
Since the ground wire is connected to the metal parts of the appliance, if the hot wire touches the metal, it creates a circuit through the ground wire.
In the circuit breaker, the ground wire and neutral wire are connected. However, the low resistance of the ground wire cannot handle the large amount of current flow, which causes the circuit breaker to trip, as it is designed to detect over-currents as a safety hazard.
One of the areas of confusion between the ground wire and the neutral wire comes from the connection between the two wires at the breaker box. Although the ground wire is connected to the ground with a metal rod, this connection is not enough to trip the breaker.
This is why the US National Electric Code Article 250 requires the ground wire to also be tied to the neutral wire at the service panel (source). To follow the current path—the current flows through the appliance ground wire to the breaker box where it joins the neutral path.
The current becomes too high at this point and the breaker trips. This connection between the neutral wire and ground wire is called bonding and is an important part of electrical safety.
The Issue of Polarity
Hot wires are red, black, or another color, while neutral wires are white. In residential codes, the neutral wire is always supposed to be grounded (connected to the ground wire). However, the idea of a “neutral” wire is actually complicated and misleading. Let’s break it down.
As I discussed, electricity flows in a circuit, so it is convenient to think of one wire being the source and one wire being the return. This is true for DC power systems (direct current, such as batteries), but residential electrical power uses AC (alternating current).
In AC systems, the flow of power is actually constantly reversing direction, roughly 50-60 times a second (source).
No appliance can tell the difference between the source and return wire, because, in reality, they don’t exist. Both wires serve both functions. In America, we have differentiated wires by having one prong of the plug, the neutral wire, bigger than the other hot wire. The ground wire is the round one on bottom.
Why do we create this distinction? Remember, one wire, the neutral wire, is connected to the ground wire. Essentially, 2 wires are grounded, so this “neutral” wire is not dangerous if exposed to metal parts like the “hot” wire is.
So to review, the neutral and hot wires are actually interchangeable as far as electrical flow through the appliance, but in America, we “polarize” the plugs to differentiate between the neutral (connected to ground) and hot wires.
We can thank Thomas Edison for this confusion. For electrical safety, while screwing in incandescent light bulbs, which have exposed threaded sockets, different-sized prongs were invented to make sure the socket was always connected to the safer, grounded, neutral wire.
What is Reversed Polarity and Why Does it Matter?
The polarization of plugs and outlets is meant to reduce the potential for shock. In our American standardization, it is impossible to reverse the polarization through plugs, as you can only insert them one way.
Note: Some appliances are double-insulated, so the chance of shock is so small they do not need to have polarized plugs—the prongs are the same size.
However, occasionally the outlet can be reversed, causing the hot and neutral wires to be backwards as far as grounding goes.
Most of the time, this doesn’t matter for safety because modern appliances are designed so that no user-accessible parts are in contact with either the hot or neutral wires.
Yet, some appliances and equipment, such as incandescent light bulbs (if you even still use these), toasters and other exposed coil appliances (ever stick a butter knife in the toaster to retrieve your toast?), and very old radios and TVs that are not double insulated, can provide a shock if touched when the polarity is reversed (source).
If you suspect reversed polarity in your home, it is worth investigating and fixing it, just for peace of mind.
You can purchase an outlet tester (link to Amazon) to quickly identify reverse polarity.
Is a Ground Wire Even Necessary?
Some people say that a ground wire isn’t even necessary because an appliance can operate normally without it, as the ground wire is not involved in the normal flow of electricity.
Theoretically, you won’t even know it if it is broken or removed—unless the metal case of the appliance comes in contact with the high voltage of the hot wire, and you touch it.
Since the hot wire shorts to the metal case, but the neutral wire, which is supposed to be connected to the ground wire, does not overload from the ground wire’s low resistance, the breaker will not trip and the appliance receives the full 120 volts, becoming a shock hazard.
So, yes, a ground wire is necessary to prevent shock and fire hazards. This can occur in many ways (source):
- Coming in contact with the hot wire while also in contact with the neutral wire will cause current to pass through your body.
- Contact with the hot wire or anything energized by it and a grounded object will cause a shock.
- Contact with electrical components or appliances that are not grounded properly can shock you.
- Contact with another person who is being shocked can shock you.
- Water is a great conductor, so standing in water, or even being sweaty, can increase your chances of shock by grounding you.
Proper Grounding and Load Capacity of Your Electrical System
According to the CDC’s Healthy Housing Reference Manual, you should have a couple of ⅝-inch copper ground rods, each 8 foot in length. (source).
The specifications get very technical and are beyond the scope of this article. Honestly, some tasks are best managed by a licensed electrician, and ensuring proper grounding of your home definitely falls into that category.
One more point:
While these techniques are used during the construction of new homes, many older homes were not built to handle a load of electricity as we use today. In the 1970s, for instance, electrical codes required a 100 amp electrical panel, while today a 200-amp panel with circuit breakers is standard.
If your home has an older electrical system, it is highly advisable to have it updated to handle the load of modern appliances without creating a fire hazard or constantly tripping breakers/blowing fuses.
Hopefully this article has explained some of the similarities and differences between the neutral and ground wire, while also explaining the importance of the ground wire in safe electrical systems.
While a ground wire and neutral wire are connected, they serve different functions in the overall electrical scheme. The neutral wire is part of the normal flow of current, while the ground wire is a safety measure in case the hot wire comes in contact with the metal casing of an appliance or other shock hazard.
By understanding the process, you can safely appreciate the modern conveniences of electricity.
Be sure to see our recommended tips on saving electricity.