Why does connecting the negative/neutral to ground not cause a 'leak?' - Page 1
Forum section: electronics / beginners

author: modointeriore
author_rank: Contributor
timestamp: October 13, 2015, 06:33:38 am
content: I have googled around for the answer to this question but the noise is so high that I cannot find an answer.I am making my way through 'practical electronics for inventors' and enjoying it very much. But when grounds are explained there is no explanation of why any circuit connected to the ground doesn't 'leak' all its charge to the ground.There are diagrams of the neutral wire of domestic AC supplies, of non-floating bench supplies, consumer electronics, etc all with a ground connected to their neutral/negative terminal. I don't understand why that doesn't provide an easier path for the current to flow to than whatever the return is. Is it because the ground can be considered charge 'neutral?' But then why ground at all? Why not, for example, wire the metallic case of a computer to an ungrounded neutral wire? I.e. it clearly provides more than a 'zero volt' reference, it is a safety feature where current does flow when something goes wrong, so why doesn't current flow there normally?I hope the question is clear enough. Thanks to anyone enlightening me!

author: IanB
author_rank: Super Contributor
timestamp: October 13, 2015, 06:39:36 am
content: Because electric current has to flow in a circuit. It always has to return to the starting point.Quote from: modointeriore on October 13, 2015, 06:33:38 amHere in your statement is the answer to the question. The current is looking for the easiest path to the return point. If it tried to go to ground instead it would be taking a detour, and perhaps would never get back to the return at all. So it a takes the shortest and easiest path back, which is directly back to the return without deviating.

author: modointeriore
author_rank: Contributor
timestamp: October 13, 2015, 06:47:01 am
content: Ok that's helpful thank you. What happens if a computer case is wired to a ground (which is in turn connected to neutral), and it then becomes 'hot?' Would the current flow down the ground wire to its connection to the neutral wire and then return along the neutral wire? Under what circumstances does a current flow to ground happen?

author: BradC
author_rank: Super Contributor
timestamp: October 13, 2015, 06:53:23 am
content: Yes, the ground completes the circuit. Current to ground happens anytime there is a complete circuit to ground. If it's a choice between ground and your hand, you want ground to be the lower impedance circuit.

author: Jeroen3
author_rank: Super Contributor
timestamp: October 13, 2015, 07:01:21 am
content: Current will not flow through ground because it isnot allowed to, by us.The energy company provides 1 Line, and 1 Neutral at your property. Sometimes 3 Lines, sometimes with or without neutral. details differ around the world. But two Lines are now very rare and often prohibited.If there is no neutral, they make one using a transformer locally, they short the neutral to ground at the transformer only.Lookup star-wye or delta wiring.Ground is a large metal pin hammered into the ground. Hence the name ground. Line and Neutral to your sockets are (or should be) protected by residual current breakers, rcd, gfci. Devices that will cut off power when current leaving through Line does not return through Neutral. Thus indicating it has a different return path thanintended, trough ground, through the water pipes, through a device which is faulty somehow, trough you. Such as with broken phone chargers or laptop chargers where chassis gets live. The protection devices trip at 30mA or 100 mA differential current. Which you can theoretically survive. However, you can sense a few mA of leakage, which is sensed as electrovibration. Which happens when you connect your pc or macbook to a non-grounded outlet, and touch the metal case with 1 finger only.It protects you when using your electric chainsaw when cutting through the wire. The blade is grounded, thus touching Line will cause the differential breaker to trip immediately. And not relying on the high current 16A breaker to trip. Which might never happen.If ground is allowed to carry current, and your example from the computer gets reality. The water pipes are suddenly part of the grid. Which is not what you'd want.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 13, 2015, 07:26:56 am
content: live and neutral wire are floating. or at least the neutral line is grounded far away from where you are at probably at the distribution transformer. ground is where you stand. current may leak to ground (or even yourself with tinggling feeling) from neutral line due to the floating nature of it or some people say "difference or higher impedance" of the neutral line, eventually the current will not get a chance to return to the source and you have earth leakage current. ELC not necessarily coming from the live line, but also from the neutral line, please bear that in mind...

author: BradC
author_rank: Super Contributor
timestamp: October 13, 2015, 10:38:18 am
content: Bear in mind the original poster is in Australia, and here we have MEN, so the neutral is bonded to ground in the premises meter box or distribution board.When giving generalizations about power systems it's often good to look at local configurations.

author: modointeriore
author_rank: Contributor
timestamp: October 13, 2015, 11:30:12 am
content: Thanks everyone. I know this is basic stuff, but I want to understand it clearly. BradC the localised response was particularly helpful, thanks.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: October 13, 2015, 12:13:21 pm
content: Your neutral wire is a real wire up to the power plant (one end of the power source) your earth connection is a parallel connections. (not a wire but really earth between it)So why bother having an earth connection?That is for safety reasons, a small leak (from the other end of the power source) trough the earth can easily be detected because the current of your neutral wire will be different from your other wire. Hence the difference went through earth (literal) this means something went wrong on your side and action can be taken to cut the power.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 13, 2015, 12:15:28 pm
content: Quote from: modointeriore on October 13, 2015, 06:33:38 amActually, it DOES. If you are talking aboutstatic charge. (The kind of charge you get in dry weather from walking in leather shoes over a wool carpet, etc.) That kind of "charge" is undesirable. It can cause electric shocks which are annoying and startling to humans, and actually FATAL to solid-state electronics which is not properly protected against ESD (electro-static discharge).QuoteDraw out the circuit. In your mind, or even on paper if that helps visualize it better. A simple circuit (a battery, switch, resistor, LED) has a complete path for the current. Whether you connect that part of the circuit to "ground" makes no difference because the path THROUGH the circuit is billions of times LOWER IMPEDANCE than any possible current path through "ground" to the crust of the planet.Quote"Ground" is considered "reference" or "neutral", or "return"by definition, and for very practical reasons.QuoteThere are several major reasons to "ground". (Or "earth" as is more common usage in BrEnglish).In many cases, earth/ground is actually used as the RETURN CONDUCTOR for power. Not in your house, but for longer-distance distribution of utility power down your street, for example. In places where utility power wires are strung along power poles in the air, if you look very carefully, you will see that the high voltage wires are strung through the air, but where they tap power off to send to your house, and your neighbors' houses, they use a step-down transformer which has one big, insulated input pole connected to the aerial wire. But the OTHER side of the circuit is a wire that travels down the pole to a ground rod. The actual crust of the earth forms the return path of the utility power to your neighborhood. This is the scheme in many parts of the planet, but not everywhere.In some places 3-phase power is distributed to users of heavier currents which is not ground-referenced. But after the transformer(s), the power that is distributed through the house or factory, etc. is grounded locally for safety. You want to provide a path for fault-current that is lower-impedance than YOU. Because if YOU are the lowest-impedance path for the fault current, it could very possibly KILL you.QuoteYes, that would work, electrically. You don't NEED to connect any part of that current loop to ground to get the power to the computer.QuoteYes, exactly.QuoteBecause the desired path for the power is a MUCH LOWER IMPEDANCE than the path to "ground". Current (like most of us) will "take the path of least resistance".