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I have a simple question about neutral and ground wire.

Since the neutral is connected to the ground, I have problems understanding the difference. Assuming it is connected to the ground, it should be just a ground?

I believe the only way it could be different is if the current can only go from the Neutral -> Ground and not the opposite?

If not, what is then the difference between both?

Cher
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4 Answers4

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The Neutral and Ground are generally connected together at your service panel, not at your devices.

At the device, neutral is the path for return current. All the current that comes "from" the hot leg "returns" through the neutral wire. I'm using quote marks because current actually alternates directions in an AC system. Hence the name AC!

Anyway, the ground wire should only carry current in the case of a fault condition. In the USA, residential ground wires are often just bare, uncovered copper. When plugging in a grounded appliance or other device, the ground wire gets attached to the chassis.

Say, for example, that the insulation on your hot wire gets damaged and the conductor comes into contact with the metal body of your washing machine. The current shorts through the chassis and then through the ground wire. This high current causes your circuit breaker (or fuse) to trip. If you didn't have the ground wire then the mains voltage would electrify the entire chassis. Then the next person touching it becomes the return path :)

bitsmack
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  • I disagree with the terminology "the return path" since it implies that the next person acts as a neutral wire while in reality he acts as a ground. – Gold_Sky May 30 '17 at 13:36
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    @Gold -- his terminology is not only correct with physicists, it's used by the NEC that way. The neutral is the nominal return path. The ground lead is an abherrent return path. Return path is the corresponding minimum inductance pathway from load to source. Further, your objection appears to confuse the concept of ground with ground wire. – DrFriedParts Jul 23 '18 at 02:55
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    Well, if neutral is connected to ground at the box, then why not just dispense with "ground" and connect the chassis to neutral? A frayed hot wire coming in contact with the chassis would similarly short and blow the fuse. – Diagon Jan 27 '19 at 00:17
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    I see - to answer my own question, if the neutral wire breaks somewhere on the return path, then the chassis will be hot. If I touch it, I might find myself surprised. – Diagon Jan 27 '19 at 03:32
  • @Diagon also, if you have an RCD, it wouldn't work properly because the earth wire goes to the earth busbar and to ground, and is not connected to neutral, which means that it doesn't flow over neutral at the busbar and instead flows to ground, which means the neutral wire has a disparity with the live wire, allowing the RCD to work. If you grounded with neutral, it would flow to the neutral bus bar and then most over the neutral wire (not earth because it has a higher resistance than neutral wire, meaning basically no disparity, only disparity is the small amount of current lost to earth) – Lewis Kelsey Apr 27 '21 at 01:40
  • Thanks, Lewis. For those not knowing what an RCD is (which was moi 5 minutes ago), I found [this](https://www.youtube.com/watch?v=qRE58D0Zh_k). (Electricians can be cool too, n'est ce pas?) – Diagon Apr 28 '21 at 05:40
  • If I don't have a circuit breaker, will grounding the chassis still protect me from a faulty insulation? – Juan Perez Jun 24 '23 at 20:22
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The ground wire is physically connected to a rod that penetrates the soil usually near the breaker box-- this is your local potential. The neutral wire goes all the way back to the source, which is usually a pole top transformer or a generator. The wire can run many miles from that grounding rod -- and can have a potential difference.

Having a separate ground and neutral has lots of safety benefits. Current should travel through that neutral and ground current should be zero. If you drop a hair dryer into a water filled sink some current gets carried to ground. Ground fault interrupters can detect this lost current and trip the circuit.

If lighting strikes all neutrals in the house get raised with the local ground potential and you and your electronics are protected. If you did not ground to that rod, the electrical appliance in your hand would still be at the remote potential of the source (possibly miles away) while you personally are raised to the lighting potential. That potential difference can shock and kill you.

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OneSolver.com
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  • You forgot to mention that it's the N-G bond at the service disconnect that provides the safety functions of grounding itself – ThreePhaseEel Jan 26 '16 at 01:51
  • "The neutral wire goes all the way back to the source, which is usually a pole top transformer or a generator. The wire can run many miles from that grounding rod -- and can have a potential difference." But wikipedia says "Neutral is usually connected to ground (earth) at the main electrical panel, street drop, or meter, and also at the final step-down transformer of the supply." That sounds a lot closer. – LarsH Mar 22 '18 at 15:26
  • I think he's saying that if neutral were *not* connected to the local ground, then a local lightning strike would raise the local potential (including me) and so if I touch neutral, which is the local potential a long way away, then I might come in for a surprise. – Diagon Jan 27 '19 at 00:25
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The ground is redundant for safety. It's not uncommon to accidentally to switch hot and neutral during installation of outlets or other things. The ground line is marked unmistakably (green or bare copper) and only has one place to attach.

In a product with a metal chassis, the chassis is normally grounded. If there were only two lines then the chassis would be attached to neutral. In the event that the hot and neutral were swapped the chassis would be electrified. Refrigerators, stoves, ovens, dishwashers are just a few things that use this system.

In products that do not have metal chassis a ground is typically not required. Further products like this are also typically double insulated.

tanner
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vini_i
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  • For more on this answer. Please see the wonderful post here: https://electronics.stackexchange.com/questions/211010/why-dont-we-use-neutral-wire-for-to-ground-devices-and-earth-wire-for-closing-t – Dave Jan 26 '16 at 01:14
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Both neutral and ground are closely related to each other, but a neutral represents a reference point within a power distribution and a return path for the current, whilst ground represents an electrical path designed to carry any fault currents if insulation breakdown were to occur. Generally the ground is used for operator safety.

Source

ZetaRift
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