The LIVE and NEUTRAL wires are both passing current and the current is reversing at 50 times a second so that they swap over the roles of positive and negative.
can i get electrocuted by holding the NEUTRAL ?
a circuit only needs two wires to be complete.
so how does the third wire - ground - fit in the circuit ?
yes
so that they swap over the roles of
no
not if all is working properly (ie not wiring faults etc)
it prevents dangerous voltages that might exist on metal parts of appliances during fault conditions by connecting them to earth
if the nutral is carrying a current at the time of you holding it then yes you can be electrocuted......nutral is the preferd method for a current to make it's return. ground or earth is a protection circuit and back at the generation site is connected to nutral.
Bob
AC current changes direction 50 times a second so the current must first flow one way - live to neutral - and then the other way - neutral to live.
no ?
er..sort of.
Yes. See above.
?
Electricity is generated three-phase:
and then for domestic supply you get one of the three live conductors, and the neutral:
If you disconnect the neutral of a circuit at any point then the neutral will be at 230v with respect to earth as there is no volt drop across the load. It could then kill you.
It changes direction because the live varies first positve with respect to neutral and then negative with respect to neutral. The neutral wire is (roughly) at earth potential and stays there (more or less - in practice under no fault conditions, there may be a few tens of volts (ac) or so on the neutral depending on the generating and distribution arrangements.
It's the size of the voltage with resepct to earth, not its sign that causes the toucher problems.
I did say the neutral wont electrocute you under no fault conditions. It is true, as another poster pointed out, that, if the neutral retrun becomes disconnected in a circuit somewhere neutrals between there and an appliance will rise to 240V if the appliance is on, giving, clearly, the risk of electric shock - this is a fault condition though.
As a practical example, our incoming mains supply comes overhead in a concentric cable. The centre inner core is the live. The outer sheath is the neutral. They are insulated from each other (obviously) and insulated overall, to guard against a) the outer becoming live under fault conditions b) unwanted neutral leakage currents to earth (which can be quite high where the impedance is very low and c) corrosion of the netral sheath. When my meter was moved, they reconnected live. The outer insulation and neutral sheath were removed/unwound and pulled back with no protective gear. The inner was then cut with a pair of extremely insulated cutters!
I have held neutrals many times under no fault conditions.
AC is usually regarded as not having positive and negative.
You can get electrocuted by holding any of the wires in a mains installation (even if its only a fault that does it). Treat all wires as though they could be live and you will survive for longer.
Not strictly true as some circuits don't need wire to complete.
Its the *most important* wire. Its there to stop some common faults killing you.
indeed. If the circuit is all perfect though then the neutral *should* be at the same potential as ground, so no current should flow. However since the neutral is definitely a current carrying conductor you shouldn't ever touch it in the first place, just in case.
C
Yep
You shouldnt do, becasue back at the electrcity sub station the nuteral is connected to the earth (and in the brown stuff outside) so everything is connected to nutral all the time.
The ground, or earth wire is only there for protection, if there was a fault in an appliance where the live or the neutral wire somehow came into contact with the metal casing of something, the current will travel down this wire instead of down the neutral wire. Now, if the wire that has become connected to the metal casing of the appliance is the Live, this is effectively shorting the live to the neutral, causing a lot of current to flow (because neutral is connected to the earth) so your fuse or little MCB (Circuit breaker) will blow/trip.
Also, if you have an RCD, this checks the current going out of the Live, and returning back via the Neutral, if there is an imbalance (because some is going to earth, maybe through a person, or the earth wire etc.) then the RCD trips.
Sparks...
Sparks
if the live wire comes loose and touches the metal case of my toaster then the current flows from the generator down the live wire , through the metal case, through the earth wire to ground, through the ground back to the generator where it goes up the earth wire there to neutral ?
when the neutral wire touches the metal case is the circuit simply totally grounded with the neutral wire at the same potential as the ground to which its connected ?
Arggh, whenever people post wikipedia links I always waste hours clicking on hyperlinks and end up learning bizarre things.
On that topic, I have a theory that in order to create the ultimate AI computer, all that is needed it to write a program that allows the machine to cross reference unknown words in text files. Then simply feed the entire contents of the OED into it and let it site there for a bit while it cross references every word in it. It will then be able to reccursively cross-reference every word and gain total and utter comprehension of the English language.
That's right - but as there isnt much resistance in this circuit, lots and lots of current flows (as it is effectivly a short circuit) so the fuse or circuit breaker will brlow/trip
yes - if you dont have an RCD, then this fault will remain undetected, but as long as the earth is all connected properly, then the toaster will still finction and you shouldnt get a shock.
If you did not have an RCD, and you connected somthing to Live and Earth, the appliace should work and nothing should blow or trip
If the circuit has an RCD, then some of the current will return via the nutral wire, but some will return through the earth. The RCD will see that there is an inbalance between the current flowing from the live and returning via the nutral (It doesnt care where it has gone, it just knows it is missing!), and it will trip. Sockets will usually have a 30mA RCD - this will trip if the inbalanace is
30mA or greater.This means, if there was a fault with your toaster where either the live or the neutral was in contact with the metal casing, but the earth wire was not connected, if you touch the metal casing, some current will be conducted through you to earth - the RCD will spot this missing current, and trip, hopefully saving your life :-)
Sparks...
30 years ago that's what we thought. Then computers started to get fast enough to do a very small amount of that task and we realised that each word didn't need simple hooks to other words but a whole word-specific program of their own. AI (true AI) is now further away than it was in the late seventies. ;-(
I don't know how she worked it out - or how much it was deliberate - but my 14 month old granddaughter calls our small dogs 'dog' and her own (much larger) dog 'dog-dog'. One of us swears that, on seeing a horse, she called it 'dog-dog-dog'. Now tell me how you'd program a computer to produce the possible grammar behind that!
Sadly not. If I say "I went up the river in a canoe", is the canoe in the river or is the river in the canoe? The only way to know which way it is, is to "know" what rivers and canoes are.
W-e-e-e-e-e-e-llll. Have a look at the CYC project, now at
I'm certain this is common in some real-world languages. Sadly, my machine translation days are long behind me, so I can't recall which ones!
I suppose the problem is that even if it could cross reference all the words, it still wouldn't actually know what any of them mean.
You'd have to create an algorithm that took factors such as the dimensions and mass of an animal and output the word dog x number of times as a result!
| if the nutral is carrying a current at the time of you holding it then yes | you can be electrocuted......nutral is the preferd method for a current to | make it's return. ground or earth is a protection circuit and back at the | generation site is connected to nutral.
Assuming proper wiring, there will only be a *small* voltage on the neutral wire, whatever current is being carried. IIRC it needs more than 30 volts to kill someone, I have personally touched 30 volt supplies more times than I care to remember without ill effects, apart from a tingle. Mind you it is a practice best avoided ;-)
Just curious. How safe is an RCD. If I stood bare footed on a damp concrete floor and grabbed the Live wire, would it still be a nasty shock but not kill me, or does it switch off so quick that I would not even notice it.
Simon
I'll want to contribute - and that will be a full-time project! When I retire ...
That's easy enough. The problem is how the easily-communicated idea developed in the first place. No one has taught her the concept of multiple words = bigger and, at the stage of hardly even having a communicable vocabulary (whilst she talks plenty I don't pretend to understand any of it - except to her!) she appears to have generated a grammar of her own. This isn't a new observation: very young children brought up in a family using (deaf) sign language will probably acquire a formal, slow, limited, grammar but - where able to converse with other, similar kids at a young enough age, develop a natural fast, open-ended grammar of their own making.
Organic life is far more proficient than any artificial equivalent that we can (yet) design.
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