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From what I'm to understand, earthed sockets send their electrons (through the neutral wire (assuming no fault)) to the circuit breaker which is then wired to earth ground. How does this work in unearthed sockets/breakers if there is no earth ground? Where is the rest of the circuit going, back to the power station?

Update 0: I was talking about wiring in the U.S.; my bad.

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  • \$\begingroup\$ @gbulmer The comments on electronics.stackexchange.com/a/185029/95654 seem to disagree. He said that they are connected in the breaker. \$\endgroup\$ Commented Jan 12, 2016 at 4:07
  • \$\begingroup\$ This might be a duplicate of Why does the power company provide a neutral line?. However, I believe this question is based on an incorrect premise; AFAIK circuit breakers do not connect neutral to earth (they detect leakage to earth) in the UK \$\endgroup\$
    – gbulmer
    Commented Jan 12, 2016 at 4:07
  • \$\begingroup\$ Sorry, I have clarified, by saying in the UK. It might be worth clarifying which locale your question applies to. AFAIK, some domestic power systems in the USA are very different. \$\endgroup\$
    – gbulmer
    Commented Jan 12, 2016 at 4:12
  • \$\begingroup\$ Okay USA. Sorry. I assume the return is back to the substation, but USA wiring is a mystery to me. \$\endgroup\$
    – gbulmer
    Commented Jan 12, 2016 at 4:22
  • \$\begingroup\$ Even with an earth ground all return current flows to neutral (except in single wire systems but AFAIK only NZ has any significant network). It is a safety earth that provides a safe path for current in case of a fault inside an appliance or wiring. It reduces the likelihood of an exposed live surface e.g. the metal case of an appliance. \$\endgroup\$
    – crasic
    Commented Jan 12, 2016 at 4:46

3 Answers 3

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You are confusing the point of the earth ground wire.

In all situations the current is supposed to flow between the phase and the neutral. The ground is just there to offer an alternative path back when a problem occurs with the live wire.

The power is generated across three phases, but that doesn't matter all that much, then at some point the neutral is connected to earth, like this:

schematic

simulate this circuit – Schematic created using CircuitLab

Now, the Earth is safe, we are all connected to it, so, nothing weird happens when we touch it. But if a device is grounded to it, and internally a phase wire comes loose and connects to a metal case, such as in a washing machine, then the current has a safe path back to neutral through the earth.

The one exception to my drawing is a single-wire system, where the Neutral is skipped in sub-station to house distribution, but that is excessively rare these days, but that would look like:

schematic

simulate this circuit

But here your house itself still has a phase, a neutral and a power earth. In some countries the neutral wire is there, but they connect to earth at the house as well, but still there will be a phase, a neutral and a ground inside the house. And a well functioning device will never conduct to ground (with the exception of earthed appliances in wet locations, such as washing machine in the bathroom - they are usually allowed to leak to ground).

Many modern systems in-house have an Earth leakage detection that trips when more than a certain current (between 5mA and 50mA usually, depending on local regulations) disappears between phase and neutral. That would mean if everything conducted to earth by default your earth leakage detector will keep tripping. This leakage detector is there to cut off the phase voltage in the case that you decide to lick a phase wire and such conduct current back to earth. That current doesn't come back through neutral, so the protector trips and saves your life.

Edit (update):

The leakage detection is connected like this, to clarify:

schematic

simulate this circuit

The current in AM1 and AM2 is compared, if there is a difference larger than a set value the switch opens. So in whatever the situation, if there is current going to earth, through the wire or through you, the switch will open.

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In the UK ...

AFAIK circuit breakers do not connect the domestic-mains neutral to earth; they do detect leakage-current to earth.

The substation distributes the three phase power to local (domestic) users, along with a neutral 'return'.

The substation connects back (eventually) to the power station. However, because of the nifty way power is distributed in the grid as three phases, their is no no need for the substation to have a neutral return to the power station.

(There are several questions on ee.stackexchange which covers the detail of three-phase power distribution, e.g. Why does the power company provide a neutral line?)

So there is no problem with unearthed sockets.
(I assume an unearthed breaker doesn't detect current leakage to earth, but I don't know how they work.)

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    \$\begingroup\$ Note that this varies by country. In some countries, neutral/return is linked to earth in the fusebox. Also, you're confusing fuses with RCDs. Fuses only 'break' when there's too much current. RCD (residual current devices) break when the difference between outgoing (on the live) and incoming (on the neutral/return) current becomes to large (generally a few mA or so). This detects leakage. Depending on type, a breaker in your fusebox can act as just a breaker, just a RCD, or both. \$\endgroup\$
    – RJR
    Commented Jan 12, 2016 at 4:25
  • \$\begingroup\$ @RJR - I understand that countries vary, that is why is say "In the UK" at the very beginning. What words in my answer confuse RCD and fuses. I am clear in my head what the difference is. \$\endgroup\$
    – gbulmer
    Commented Jan 12, 2016 at 4:28
  • \$\begingroup\$ You didn't confuse them - just not mention them. 'Circuit breakers...detect leakage-current to earth' - that's only true for those with a combined fuse/RCD function. \$\endgroup\$
    – RJR
    Commented Jan 12, 2016 at 4:34
  • \$\begingroup\$ Strictly speaking, RCD devices detect an imbalance between current supplied (on the live) and current returned (on the neutral), rather than an actual leak to ground - of course the imbalance is usually caused by a leakage to earth. \$\endgroup\$
    – Icy
    Commented Jan 12, 2016 at 8:58
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This is calssic EU house wiring, live and neutral.

schematic

simulate this circuit – Schematic created using CircuitLab

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