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Lim Y K
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Why must a switch be at the live wire instead of the neutral wire?
Take the classic example of an electric toaster and a person in a bathtub. If you turn off the wall outlet with a switch on the live wire, the person in the bathtub is (reasonably) safe. If you turn off the wall outlet with a switch on the neutral wire, the person in the bathtub is at risk.Lim Y K said:In what way does that make the appliance safe?
In addition, if the wall outlet had its switch break the neutral line and not the active, then every unoccupied socket even though switched to "off" would expose a dangerous voltage to the idle probing of inquisitive toddlers (and pets).Lim Y K said:Why must a switch be at the live wire instead of the neutral wire?
In the UK all domestic sockets must be fitted with shutters which prevent contact with the live (or neutral) supply unless there is a pin in the Earth socket. The idea that a socket is made safer from an inquisitive child's fingers by providing a switch which the same child can easily operate is ludicrous.NascentOxygen said:Notwithstanding the hazard, some countries, I understand, do allow wall outlets without an associated switch; you have to plug and unplug from a constantly "live" socket. So try to keep fingers clear!
The most basic hazard with electricity is providing an alternate path to ground. If you grab a grounded wire then your body is just part of the ground. If you grab a live wire then your body may form a path to ground. By switching on the live side you make most of the wiring grounded when it is off, and only a small part of the wiring is live. Thus if you grab a random section of wire you are less likely to have grabbed a live wire if the switch is on the live side.Lim Y K said:In what way does that make the appliance safe?
the simple answer is if the circuit is switched on the neutral, then when the circuit is 'OFF' the load is still "LIVE" (at mains voltage).Lim Y K said:In what way does that make the appliance safe?
mr166 said:BTW just because a wire is white that does not mean it is a neutral. Here in the US it is very common to have 220V wiring that has black and white hot wires. The black measures 110v to ground and the white measures 110v to ground. They are 180 degrees out of phase so you measure 220V across the black and white wires.
One of those countries is the US. Switched outlets are unusual.NascentOxygen said:Notwithstanding the hazard, some countries, I understand, do allow wall outlets without an associated switch; you have to plug and unplug from a constantly "live" socket. So try to keep fingers clear!
To compensate for this, some of the outlets like ones in a bathroom or laundry room (any room that could have water on the floor) have ground fault interrupters. Wiki article:insightful said:One of those countries is the US. Switched outlets are unusual.
sophiecentaur said:There was a time when some electrical equipment had internal fuses in both the live and the neutral lines. I can't think why that idea ever caught on. I have actually used such equipment which had been modded to eliminate the neutral fuse.
And what is the rationale behind that? If the two conductors are truly floating then 1. how does the fuse provide a protection against shock and 2. How does an extra fuse in series do a better job of overload protection? There must be some scenario that prompted double pole fusing but I can't think of one at this minute.nsaspook said:I know that US military ships use floating AC for power, there is no neutral wire so both wires (single phase) are 'HOT' and are fused.
My two cents:sophiecentaur said:And what is the rationale behind that? If the two conductors are truly floating then 1. how does the fuse provide a protection against shock and 2. How does an extra fuse in series do a better job of overload protection? There must be some scenario that prompted double pole fusing but I can't think of one at this minute.
Damage control? Never know which side of a circuit's going to be open to salt water?sophiecentaur said:rationale behind that?
nsaspook said:I know that US military ships use floating AC for power, there is no neutral wire so both wires (single phase) are 'HOT' and are fused.
The requirement ashore is the safety of human beings. So, inorder to prevent human-electrical accidents, the neutral is earthed. The priority is neither the safety of the machinery nor the continuous necessary operation of the machinery. But the scenario onboard ship is totally different. The priority is the continuous operation of the machineries which are classed "essential". The distribution system followed onboard is "insulated neutral" system. The main priority onboard is the safety of ship which includes navigation & fire safety..etc. If due to Earth fault, the machinery classed as"essential" gets isolated, say for eg: steering gear, then the safety of ship is at question, which may lead to collison, grounding, fire & pollution etc..So the priority onboard ship is to maintain the continuity of the supply to the machinery in the event of "single Earth fault occurring". Continues..
sophiecentaur said:There was a time when some electrical equipment had internal fuses in both the live and the neutral lines. I can't think why that idea ever caught on. I have actually used such equipment which had been modded to eliminate the neutral fuse.
That sounds dangerous. Like the kind of thing where you might touch the spotlight with one hand and something correctly grounded with the other and get a serious shock.tfr000 said:Simple example... I once repaired a spotlight lamp in a garage. When you operated the switch, it would go from bright to dim instead of from on to off. I found that the switch had been wired into the neutral side. The lamp current was obviously finding another path to ground when the neutral was interrupted. I moved the switch to the hot side, problem solved.
FactChecker said:That sounds dangerous. Like the kind of thing where you might touch the spotlight with one hand and something correctly grounded with the other and get a serious shock.
CWatters said:
Alternating current travels in a circular path along the "hot" and the neutral conductor. The switch breaks the circuit in the hot.Lim Y K said:Why must a switch be at the live wire instead of the neutral wire?
where?mr166 said:WW you are 100% wrong.
It's really best if you realize that, as far as the generator and the load are concerned, there is no difference or order of importance between the two conductors. The Potential Difference between them just alternates at mains frequency. The fact that one of the wires happens to be connected to (or near) Earth has no effect whatsoever on the way the circuit works. Current flows alternately clockwise and anticlockwise. If you connect your 'scope probe to the live wire, its voltage will oscillate about zero volts and the neutral wire will have, nominally, no voltage swing relative to Earth. If you uncouple the Neutral back at the transformer, the two voltages will still waggle about and the difference between the two voltage waveforms will still the 'mains voltage' waverform but the absolute value of the mean between the voltages could be anything, depending on where one of the lines happens to be connected. The term Potential Difference says it all.puf_the_majic_dragon said:So, basically, a generator has a magnet more or less "pushing" electrons around a coil of wire. In order for those electrons to respond to the "push", they need a place to go, hence a closed circuit with a source and return. Now I understood AC generators to more-or-less change the direction that they "push" the electrons in, which would mean that on the down phase the return wire became the source wire, and thus both wires could be "hot". But if the neutral is earthed, whether at the breaker panel or a grid transformer, then it could never possibly be hot - which leaves me wondering where the heck does the hot wire in an AC grid get its electrons? My hypothesis might be that on the down phase the generator is "pulling" electrons instead of pushing them, kind of creating an electron vacuum along the coil. Yes? No? I know I'm using layman's parlance, but I'm not afraid of a more technical explanation.
Which is what confuses me, since that means the "neutral" is no different from the "hot".sophiecentaur said:It's really best if you realize that, as far as the generator and the load are concerned, there is no difference or order of importance between the two conductors.
"Current" and "Charge", in this context, are rather abstract terms. I've known way too many electricians who use the words "current" and "charge" and don't have a clue what an electron is, much less what either word really means. Of course electrons do crazy things - this is a physics forum, after all, so why should we not talk about the crazy things they do?PS, many people feel that using the term 'electrons' somehow makes posts more learned or easier to understand. If you look at the wording used by 'people wot know', you will notice that they very seldom use electrons in explanations. They nearly always use the terms 'Current' and 'Charge'. because the nature of the charge carriers is not relevant in 99.9% of circuits. Electrons are far too hard to cope with when dealing with circuits. They do so many strange things.
Exactly. And neither, I suggest, do you have a solid grasp of what they truly are (along with the vast majority of us). I would venture to say that you probably see them as tiny charge carriers. Does your understanding the way circuits work involve anything more than the charge on an electron? So why not avoid the term - which can only add complication - and use the accepted terms, using the Joule and the Amp instead of the number and rate of electrons? Like I said, it's common practice and there's a very good reason for it. It is not a cop-out to use the 'right' terms.puf_the_majic_dragon said:and don't have a clue what an electron is,