mrapple@quack.sac.ca.us (Nick Sayer) (01/12/91)
The radio shmuck testers seem to say, and a volt meter seems to prove, that there is an AC potential between hot and ground and hot and neutral, but there is no potential between neutral and ground. Now ground and neutral clearly are not the same thing. I would expect negative side effects were I foolish enough to hook a light bulb between hot and ground. But wait! In AC, every half cycle the current goes the other way! So why isn't there a potential between neutral and ground? Inquiring minds want to know! What, exactly is the theory here? Ground is connected (basically) to a big pipe in the dirt, and hot and neutral go up to the pole, but some more details for a complete software weenie would be great. -- Nick Sayer | Think of me as a recombinant | RIP: Mel Blanc mrapple@quack.sac.ca.us | Simpson: Homer's looks, Lisa's | 1908-1989 N6QQQ [44.2.1.17] | brains, Bart's manners, and | May he never 209-952-5347 (Telebit) | Maggie's appetite for TV. --Me | be silenced.
henry@zoo.toronto.edu (Henry Spencer) (01/13/91)
In article <kJhTxoE@quack.sac.ca.us> mrapple@quack.sac.ca.us (Nick Sayer) writes: >What, exactly is the theory here? Ground is connected (basically) >to a big pipe in the dirt, and hot and neutral go up to the pole, >but some more details for a complete software weenie would be >great. The current flows through hot and neutral. Ground is strictly for safety purposes and never (deliberately) carries current. Neutral is normally grounded at the pole. Note, however, that with tens or hundreds of amps of current flowing in neutral, it is *not* at ground by the time it gets to you. V=IR, and the wire's R is not zero. Neutral can be very close to ground in a house that isn't pulling much current. (Beware, this can change unpredictably, e.g. when your housemate puts a load of washing into the dryer.) It can be several volts above ground in upper floors of an apartment building; I've measured it. Neutral is not *as* dangerous as hot, but it should never be mistaken for ground. This is why there is a separate ground pin, for safety. -- If the Space Shuttle was the answer, | Henry Spencer at U of Toronto Zoology what was the question? | henry@zoo.toronto.edu utzoo!henry
k3tx@wells.UUCP (Dave Heller) (01/13/91)
In article <kJhTxoE@quack.sac.ca.us>, mrapple@quack.sac.ca.us (Nick Sayer) writes: > The radio shmuck testers seem to say, and a volt meter seems > to prove, that there is an AC potential between hot and ground > and hot and neutral, but there is no potential between neutral > and ground. > > Now ground and neutral clearly are not the same thing. I would > expect negative side effects were I foolish enough to hook > a light bulb between hot and ground. > > But wait! In AC, every half cycle the current goes the other > way! So why isn't there a potential between neutral and ground? > Inquiring minds want to know! > > What, exactly is the theory here? Ground is connected (basically) > to a big pipe in the dirt, and hot and neutral go up to the pole, > but some more details for a complete software weenie would be > great. > > -- > Nick Sayer | Think of me as a recombinant | RIP: Mel Blanc > mrapple@quack.sac.ca.us | Simpson: Homer's looks, Lisa's | 1908-1989 > N6QQQ [44.2.1.17] | brains, Bart's manners, and | May he never > 209-952-5347 (Telebit) | Maggie's appetite for TV. --Me | be silenced. There should be a continuous hot and return path for the actual power consumed. There should also for safety and many other considerations be a solid GROUND throughout the system. It is a fact that the so-called NEUTRAL is at ground potential, so technically shorting Neutral to Ground should be a zero-current affair. As a practical matter, NO. The Neutral is at "steady state ground" but may not be at the transient ground, especially under fault conditions. Neutral WILL be grounded, but at one place only, generally a ground rod below the service entrance. And this should be the only place. Continuity of ground is most important, however. Much new construction uses non-metallic (i.e., plastic) junction boxes, for which grounding is rather difficult. In my opinion the use of plastic boxes is a damn foolish way of economizing just a little bit. However, most contractors use the cheapest devices and junk they can get, on the premise that not every house miswired is going to catch fire (just a few) and that not every ;house fire does a lot of damage or kills somebody -- just a few, so the hell with it because they got paid for the job long since. Suggestion: what some "professional" electricians do is bad enough, but the doityourself stuff is often worse. If you have to ask, don't try doing it without EXPERT supervision. K3TX
tad@ssc.UUCP (Tad Cook) (01/14/91)
In article <kJhTxoE@quack.sac.ca.us>, mrapple@quack.sac.ca.us (Nick Sayer) writes: > > Now ground and neutral clearly are not the same thing. I would > expect negative side effects were I foolish enough to hook > a light bulb between hot and ground. Ground and neutral are hooked together at the electrical service entrance or on your breaker panel. > > But wait! In AC, every half cycle the current goes the other > way! So why isn't there a potential between neutral and ground? > Inquiring minds want to know! The shift in current direction has nothing to do with it, but actually there usually is a small potential between ground and neutral at an outlet, depending on the load and the wire resistance. Tad Cook Seattle, WA Packet: KT7H @ N7HFZ.WA.USA.NA Phone: 206/527-4089 MCI Mail: 3288544 Telex: 6503288544 MCI UW USENET:...uw-beaver!sumax!amc-gw!ssc!tad or, tad@ssc.UUCP
robf@mcs213k.cs.umr.edu (Rob Fugina) (01/15/91)
In article <kJhTxoE@quack.sac.ca.us> mrapple@quack.sac.ca.us (Nick Sayer) writes: >Now ground and neutral clearly are not the same thing. I would >expect negative side effects were I foolish enough to hook >a light bulb between hot and ground. Ground and neutral are exactly the same thing. If you were to trace the wires back to your breaker box, you would find bare wires (ground) and white wires (neutral) both connected to a grounding strip. The hot wire's potential varies from ~170V above ground to ~170V below ground. The two wires that come from the pole are both hot, BUT, the sine waves are 180 degrees out of phase with one another, so when one is at +170, the other is at -170, and if you connect something to those two, you will have a 340V sine wave. (values are peak, not RMS...RMS would be about 120 and 240). MY QUESTION is, if you don't have 3-wire connections in your house, why can't you connect the white wire to the ground lug and conuit/boxes, etc??? Rob robf@cs.umr.edu
bender@oobleck.Eng.Sun.COM (Michael Bender) (01/15/91)
In article <1948@umriscc.isc.umr.edu> robf@mcs213k.cs.umr.edu (Rob Fugina) writes:
->Ground and neutral are exactly the same thing. If you were to trace the
->wires back to your breaker box, you would find bare wires (ground) and
->white wires (neutral) both connected to a grounding strip.
^^^^^^^^^^^
anyone know why they choose BLACK for the hot wire and WHITE for
neutral? I always associated black wires with ground.
mike
--
Won't look like rain, Won't look like snow, | DOD #000007
Won't look like fog, That's all we know! | AMA #511250
We just can't tell you anymore, We've never made oobleck before! | MSC #298726david@cs.uow.edu.au (David E A Wilson) (01/15/91)
bender@oobleck.Eng.Sun.COM (Michael Bender) writes: >anyone know why they choose BLACK for the hot wire and WHITE for >neutral? I always associated black wires with ground. I wondered about that too when I saw some North American terminals over here in Australia. We used RED (now BROWN) = Active, BLACK (now BLUE) = Neutral and GREEN (now GREEN with YELLOW stripe) and all the terminals had neutral and active swapped (presumably when the importer installed the Australian crow foot* plugs). The new colours are the IEC standard. * Active / \ Neutral (facing power socket) | Ground (10 Amp General Purpose Outlet) (15 Amp has larger earth pin) (20 Amp has all pins larger) -- David Wilson Dept Comp Sci, Uni of Wollongong david@cs.uow.edu.au
whit@milton.u.washington.edu (John Whitmore) (01/15/91)
In article <1948@umriscc.isc.umr.edu> robf@mcs213k.cs.umr.edu (Rob Fugina) writes: >In article <kJhTxoE@quack.sac.ca.us> mrapple@quack.sac.ca.us (Nick Sayer) writes: >>Now ground and neutral clearly are not the same thing. I would >>expect negative side effects were I foolish enough to hook >>a light bulb between hot and ground. One easily seen effect would be the tripping of the GFI (ground- fault interrupter) on that circuit. All kitchens, baths, and outdoor sockets (including sockets in unheated garages) must be GFI-connected nowadays. The GFI looks at the current in the HOT minus NEUTRAL wires, and if the difference is nonzero, it trips just like a breaker would trip during a short circuit. > >Ground and neutral are exactly the same thing. If you were to trace the >wires back to your breaker box, you would find bare wires (ground) and white >wires (neutral) both connected to a grounding strip. Wrong place to look. The appliances take current from HOT and return the current through NEUTRAL to complete the circuit, NEVER putting any current through GROUND except in a sparks-flying fault condition. As a result, the far end (away from the breaker panel) of the NEUTRAL wire will exhibit I*R voltage due to the current drawn (and a cheap Skilsaw can easily top 50 amperes for a few milliseconds in normal starting). The resistance and inductance of the neutral wire will cause some voltage drop (16VAC is not unheard of). Just because ONE end is connected to ground, doesn't mean the wire is grounded! The ground wire has no other connections, barring faults, so connecting one end to ground IS sufficient. > The two wires that come from the pole are both hot, Miscount! Three wires come from the pole: two phases of 120 VAC and neutral. That neutral wire is grounded to the same water pipe and grounding block in your breaker box as the ground and neutral wires connect to. The omission of the neutral wire would require perfect current balance between 120V appliances on the two phases (not likely.) All the houses on the block will typically have ground connections for that neutral wire, so losing one connection might not have immediate consequences, though. I am known for my brilliance, John Whitmore by those who do not know me well.
jws@cica4.mlb.semi.harris.com (James W. Swonger) (01/15/91)
In article <5884@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (Michael Bender) writes: > >anyone know why they choose BLACK for the hot wire and WHITE for >neutral? I always associated black wires with ground. > I think it was done that way because the average schmoe associates black with death, i.e. "don't touch that one, dummy"
mcovingt@athena.cs.uga.edu (Michael A. Covington) (01/16/91)
Ground and neutral are supposed to be connected together at the transformer. That's why there's never a substantial potential difference between ground and neutral. Incidentally, "every half cycle the voltage goes the other way" has nothing to do with it. It reverses polarity, but it's still connected across exactly the same wires. The power for your house comes out of a 220-volt-center-tapped transformer winding with the center tap grounded, and connected to Neutral. Live is _either_ of the other 2 transformer wires, depending on which circuit of your house you happen to be looking at.
dmturne@PacBell.COM (Dave Turner) (01/16/91)
In article <5884@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (Michael Bender) writes: >anyone know why they choose BLACK for the hot wire and WHITE for >neutral? I always associated black wires with ground. The standard of BLACK and WHITE for power probably predates that for other electronic wiring where BLACK is ground and RED is hot (such as that used in old vacuum tube devices). Perhaps a better question is why did the later standards ignore (and violate) the earlier one(s)? -- Dave Turner 415/823-2001 {att,bellcore,sun,ames,decwrl}!pacbell!dmturne
myers@hpfcdj.HP.COM (Bob Myers) (01/16/91)
>Ground and neutral are exactly the same thing. If you were to trace the >wires back to your breaker box, you would find bare wires (ground) and white >wires (neutral) both connected to a grounding strip. The hot wire's potential >varies from ~170V above ground to ~170V below ground. The two wires that come >from the pole are both hot, BUT, the sine waves are 180 degrees out of phase >with one another, so when one is at +170, the other is at -170, and if you >connect something to those two, you will have a 340V sine wave. (values are >peak, not RMS...RMS would be about 120 and 240). Well, they're the "same thing" before you have any current, but they're definitely NOT the same thing from that point on. The difference is that the "white wire" neutral is the *intended* return path for current on the circuit; as such, it is always, at any outlet on the branch, at some potential above ground due to the effect of such current and the resistance of the neutral wire (E=IR, right?). It is NOT "guaranteed" to be at zero volts. The "green wire" ground, though, normally carries no return current, and so is always at a lower potential - zero, unless some current is flowing in the ground wire due to a fault condition. The idea to to give the lowest possible potential on the "ground" wire in the event that a fault does occur, and so requires this wire to carry return current. >MY QUESTION is, if you don't have 3-wire connections in your house, why >can't you connect the white wire to the ground lug and conuit/boxes, etc??? See why now? You DON'T want the ground wire to normally be carrying return current, or else it would be at some potential above "ground "at the outlet. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers@fc.hp.com | sentient life-form on this planet.
murray@sun13.scri.fsu.edu (John Murray) (01/16/91)
In article <1991Jan15.142034.5801@mlb.semi.harris.com> jws@cica4.mlb.semi.harris.com (James W. Swonger) writes: >In article <5884@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (Michael Bender) writes: >> >>anyone know why they choose BLACK for the hot wire and WHITE for >>neutral? I always associated black wires with ground. >> > I think it was done that way because the average schmoe associates >black with death, i.e. "don't touch that one, dummy" US Three-phase color coding: GReen=GRound White=Neutral (white is sorta a neutral color, I guess..) Black=Phase 1 Red=Phase 2 Blue=Phase 3 Working with 50, 100,...,1200 amp AC three-phase services, I have seen these colors used a whole lot. I have also seen black=ground, red=hot... in low-voltage DC electronics. They're pretty much different critters, so the color confusion doesn't bother me much. Kinda hard to confuse black 0000 gauge with black 24 gauge wire :-) Anyway, this is where the green(or bare)=ground, white=neutral, black=hot color scheme for three wire AC cables comes from. -- Disclaimer: Yeah, right, like you really believe I run this place. John R. Murray | "Never code anything murray@vsjrm.scri.fsu.edu | bigger than your head.." Supercomputer Research Inst.| - Me
steve@nuchat.sccsi.com (Steve Nuchia) (01/16/91)
In <1948@umriscc.isc.umr.edu> robf@mcs213k.cs.umr.edu (Rob Fugina) writes: >Ground and neutral are exactly the same thing. If you were to trace the And more dangerous speculation. It probably doesn't need to be said here, but I'll feel better if I say it anyway: If you don't know that you know what you're doing, don't play around with your wiring. There. I do feel better. Now, I'll lay it all out for reference. This isn't electronics, but maybe it will enlighten some, and help others avoid being lit up :-) Power wiring is always discussed in nominal RMS, peak is of interest only when engineering insulation and protection systems. 99.999% of all wiring is done using pre-engineered components which have their voltage and current ratings tabulated in nominal RMS terms in catalogs and handbooks and such. Residential service is normally provided from overhead or buried high voltage distribution lines through a transformer serving one or several subscribers. The distribution is often a 3-phase Y, but rural branches may have only one power conductor plus the ground return. Several other arrangements can be used to suit the power company's needs. Distribution lines are typically in the 15 - 45 kV range. The distribution circuit is protected by overcurrent devices and ground-fault detection devices at the substation, but it takes one heck of a fault to open those. The subscriber transformer primary is often wired from one phase to neutral on the distribution side, but phase-to-phase is sometimes used. If you have three-phase service (normally the case only for industrial and large commercial customers) the transformer primary is attached to all three distribution phases (and maybe neutral). Autotransformer configurations are also used, I believe. The residential transformer secondary is a single phase 240 volt center tapped winding. The center tap is coupled at the pole to a ground rod and to the service drop neutral conductor. This positively limits the voltage on the service cables, relative to ground, to a few times the nominal service voltage. It also ensures that a core short will draw enough current to open an upstream protection device. The three wire single phase service entrance cable passes through the meter and into the customer's distribution panel. There the neutral is again bonded to grounds, including the frame if it is a metal building. This limits the voltage present on the interior wiring relative to ground -- if the service were not gounded the whole circuit would float. The rules for what should and should not be grounded, and where, and how, are complex. Not terribly technical, but lots of cases and exceptions have to be dealt with. In general, neutral and ground are bonded at the service entrance and kept separate throughout the rest of the interior wiring system. The cable system from the transformer to the meter, together with the transformer secondary winding, is capable of delivering some calculable short circuit current. There should be an overcurrent protection device somewhere in the circuit capable of interrupting that much current. It is typically in the 10-20 thousand amp range, and typical residential breaker box panels should have a main breaker or fuse rated to handle the maximum allowble short circuit current for a residential service drop. If the overcurrent protection device is a fuse there should also be a master disconnect switch. The distribution panel supplies the two "phases" to the branch breakers in an alternating pattern. 120V branch circuits are assigned essentially at random to the two sides of the supply, 240V circuits use dual breakers straddling the two phases. Due to I^2R losses it is best to balance the loads as much as possible, but people seldom bother. Many breaker boxes are arranged in such a way that only certain positions will accept a 240V circuit, or it will only work in certain positions. If you ever have to work inside a breaker box you should be able to puzzle out its configuration rules just by looking at it. Note that the dual breakers for 240 circuits (and tripples for 3-phase) are not just two single breakers with their handles wired together. The trip mechanisms are connected internally so they open both sets of contacts together more reliably than can be achieved by tying the handles together. Examining the interior wiring plant as a circuit, we have several loops carying varying amounts of current. Many of those loops involve the neutral conductor, some are balanced 240V loads. The neutral current on any given 120V branch circuit is the same as the supply current. The overall current in the service neutral is the difference of the currents in the two supply wires. Interior wiring is normally designed with voltage drops in the wires of no more than a couple of volts, so the neutral at an outlet is normally very near the ground potential at that outlet. Ok. Now it get interesting. Power system engineers earn their feed by saving money in normal operation and saving lives and property in fault conditions. An electrical distribution system with a fault looks very little like the nice little circuit model you might think it should resemble. Lets take three fault scenarios. Consider an open neutral in a branch circuit. That neutral conductor, on the load side of the fault, now carries 120V with the load in series limiting the current. If that condutor is exposed downstream of the fault a life-threatening hazard exists. It bears repeating that the minimum lethal dose of electric current is in the 20 mA range. A dangling neutral with a 100W bulb in series can supply 50 times that (ignoring the fact that the filament is cold). A few volts between the cold water supply and the drain pipe can kill a person in the bath tub. Consider a fault to neutral -- a common scenario. Hundreds of amps flow through a circuit designed for 15, and you get tens of volts dropped in the neutral. Not only resistive voltage drop needs to be considered -- there is a considerable inductance in the loop. Now if there are multiple connections between the neutral and various "ground" points there will be currents flowing in those grounds, which have non-negligable resistance. different pieces of the ground network will be at different potentials, and unless one controls the geometry carefully (no one does), those pieces may be close enough together for people to short themselves between them. Yes, the overcurrent protection device will open, but it will take at least a few milliseconds and possibly several hundred. Consider a fault to the chassis of an appliance. Nah, lets leave off with the above. In a ground fault scenario it doesn't make much difference how the neutral is wired. That's why we have ground fault detectors. By the way, in addition to the ground fault receptacles now available (and required for bathrooms) you can get ground fault circuit breakers for most kinds of panels. Pricey ($40ish) but it might come in handy sometime. You can also get breakers with remote control inputs or (and?) alarm outputs. Get creative. The important thing to remember is that you have to forget the idea that a wire is a node. Wires are distributed resistive+inductive circuit elements with several potential failure modes. And ground is a network, not a node. It's a lot like RF. If any of the above comes as a surprise, you should probably limit your electrical handy-man efforts to replacing dead parts in existing circuits and maybe cook-booking low current (<= 20 A) branch circuits. Find and *use* a cookbook though, don't try to wing it. And don't believe the salescritters at the hardware store either. Some know what they're talking about, but unless you know what they're talking about you can't tell them apart from the ones who don't. If you want to do something that is beyond your certain knowledge, get out the phone book and call some of the small (ie, one-man) electricians. Chances are you can find one who will agree to check your work (and/or plans). You save money and still have the comfort of a journeyman's OK. Do I need to add that you shouldn't expect to get his time for free? Finally, I've probably messed up some of the above. With probability 1, I'm misusing some technical terms. I'm not interested in being corrected about trivial things, though substantive corrections are most welcome. This is not a professional opinion. You get what you pay for. Be careful out there. -- Steve Nuchia South Coast Computing Services (713) 964-2462 "Could we find tools that would teach their own use, we should have discovered something truly beyond price." Socrates, in Plato's Republic
adrian@cs.hw.ac.uk (Adrian Hurt) (01/16/91)
In article <1991Jan14.223300.8560@cs.uow.edu.au> david@cs.uow.edu.au (David E A Wilson) writes: >bender@oobleck.Eng.Sun.COM (Michael Bender) writes: >>anyone know why they choose BLACK for the hot wire and WHITE for >>neutral? I always associated black wires with ground. > >I wondered about that too when I saw some North American terminals over here >in Australia. We used RED (now BROWN) = Active, BLACK (now BLUE) = Neutral >and GREEN (now GREEN with YELLOW stripe) ... Right, let's have some confusion. Here is what our booklet on safety regulations lists for international "standards": ------------------------------------------------------------------------------ 2 wire cable 3 wire cable Live Neutral Live Neutral Earth Great Britain Brown Blue Brown Blue Green & Yellow Canada Black* White or Black White or Green & Grey Grey Green Yellow Denmark Black* Blue Brown or Blue Green & Yellow Black Finland Black or Blue Brown Blue Green & Yellow Brown Greece Anything Grey Anything Grey Yellow except except Grey, Grey, Yellow Yellow or Blue or Blue Japan Black White Black White Red Poland Black* Blue Black Blue Green & Yellow Switzerland Anything Anything Brown Blue Green & Yellow except except Yellow Yellow and Blue and Red USA Black* White or Black White or Green or Grey Grey Green & Yellow *Black for live in 2 core cords is now being replaced by Brown. ------------------------------------------------------------------------------ My list doesn't include Australia, who being upside down use black for neutral, because it isn't in our book. So much for our book. Note that Japan is listed as using red for earth! Also note that Switzerland's entry for 2 wire cable looks nasty - taking this list literally, they could quite happily use black and white for live and neutral in any way they choose. In general, black or brown seems to always be live (except in Australia); blue, white or grey is always neutral; green, yellow or a mixture is always earth. "Keyboard? How quaint!" - M. Scott Adrian Hurt | JANET: adrian@uk.ac.hw.cs UUCP: ..!ukc!cs.hw.ac.uk!adrian | ARPA: adrian@cs.hw.ac.uk
k3tx@wells.UUCP (Dave Heller) (01/17/91)
In article <1991Jan16.035358.28312@nuchat.sccsi.com>, steve@nuchat.sccsi.com (Steve Nuchia) writes: > > And more dangerous speculation. > > If any of the above comes as a surprise, you should probably limit > your electrical handy-man efforts to replacing dead parts in existing > circuits and maybe cook-booking low current (<= 20 A) branch circuits. > Find and *use* a cookbook though, don't try to wing it. And don't > believe the salescritters at the hardware store either. Some know > what they're talking about, but unless you know what they're talking > about you can't tell them apart from the ones who don't. > > If you want to do something that is beyond your certain knowledge, > get out the phone book and call some of the small (ie, one-man) > electricians. Chances are you can find one who will agree to check > your work (and/or plans). You save money and still have the comfort > of a journeyman's OK. Do I need to add that you shouldn't expect > to get his time for free? > > Finally, I've probably messed up some of the above. With probability 1, > I'm misusing some technical terms. I'm not interested in being corrected > about trivial things, though substantive corrections are most welcome. > This is not a professional opinion. You get what you pay for. > Be careful out there. > -- > Steve Nuchia South Coast Computing Services (713) 964-2462 The only thing in Steve's posting I take issue with is his disclaimer. He hasn't messed up -=- a nice job of describing what seems to the high tech boys as something as complicated as a doorbell circuit. The routing by which some sort of energy is converted to the juice in our wall plugs, the technology and the work schedules of ALL those in the industry has to be lived with to be appreciated. The miracle is that it is kept as dependable as it is, and that there are so few instances of property damage and injuries associated. And, really, most of this latter is traceable to the Do-It-Youself-ers and the lower levels of self-defined professionals. As in every other essential field, the really good people are hard to find, but end up being the cheapest. How do you find them? Good question. They work by referral. Only the people who can't get referral and repeat business need big advertising, so in general, the bigger the yellow pages ad the poorer the quality. (The extreme is the tradesman or professional with unlisted phone. It does happen.) One good caveat: Don't pay any mind to the UL label on electrical devices. Look for the CSA (SA in a broken circle = C). The Canadians are much more realistic in deciding what's safe to use than USA. Please note that many of the cheapie switches and receptacles at the hardware store LACK the CSA marking. This is a good indication that they'd be over priced if they were FREE. I don't like the idea of the d-i-y doing his own house wiring or repairs even with cookbook in hand. I've seen too many bad, and some VERY bad results. A competent hands-on engineer certainly should be able to do any wiring work. Experience and practical engineering skills are more important than being able to read the cookbook. But the general rule should be: If y ou have to ask, don't try to do it.
ahlenius@motcid.UUCP (Mark Ahlenius) (01/17/91)
robf@mcs213k.cs.umr.edu (Rob Fugina) writes: >In article <kJhTxoE@quack.sac.ca.us> mrapple@quack.sac.ca.us (Nick Sayer) writes: >>Now ground and neutral clearly are not the same thing. I would >>expect negative side effects were I foolish enough to hook >>a light bulb between hot and ground. Actually, the bulb will work fine. By using a pig tail lamp (100w) its a good idea to make sure that the bulb works fine between hot and ground - as this checks out the ground path to make sure it is a good connection. Note that is the circuit being tested is a gfi (ground fault interrupter) this will (should) cause the unit to trip. >Ground and neutral are exactly the same thing. If you were to trace the >wires back to your breaker box, you would find bare wires (ground) and white >wires (neutral) both connected to a grounding strip. The hot wire's potential >varies from ~170V above ground to ~170V below ground. The two wires that come >from the pole are both hot, BUT, the sine waves are 180 degrees out of phase >with one another, so when one is at +170, the other is at -170, and if you >connect something to those two, you will have a 340V sine wave. (values are >peak, not RMS...RMS would be about 120 and 240). If you check a copy of the NEC (National Electric Code) you will find out that neutral and ground are not the same thing. Note that these comments really only apply to the United States code. Yes it is true (at least in the Chicago area) that the neutral wire upon entrance to a building is to be "bonded" or tied to the chasis of the circuit panel. This is usually done via a small bonding lug that comes out of the neutral bus bar and gets connected to the chasis of the panel. A wire then connects from the neutral bus to the street side of the water pipe (if metallic) or to a series of ground stakes. This is the ONLY place that neutral and ground should be in common in the building. The emt (conduit) or bx sheath, or ground wire of romax (etc.) is not intended to be a normal current carrying circuit. It is there as a safety ground such that if an appliance fails (loose wire, meltdown, etc) the ground will short out the fuse or breaker and stop any further problems. The neutral wire is intended to be a normal current carrying circuit (is sometimes called the return path - although in a.c. its ...). If you attach a neutral wire to ground anywhere else in your building, you can create ground loops which I wont go into here. >MY QUESTION is, if you don't have 3-wire connections in your house, why >can't you connect the white wire to the ground lug and conuit/boxes, etc??? A very dangerous idea. Besides being illegal (against local and national codes) it could prove very dangerous. Many appliances (like washers & dryers) have their chasis tied to earth ground. If you tie the neutral wire to the ground lug on the outlet, you have essentially tied the chasis to neutral. Because the neutral wire is current carrying, it is possible that due to resistance in the wire (IR drop) and/or poor connections that a voltage drop may exist between the neutral at the outlet and your circuit panel. Now if someone (like a small child) brushes up against the chasis and happens (and it does happen) to touch a water pipe - a nice shock can be had! Electrical work is really pretty easy stuff. And because engineers and techs have an understanding of electronics - they often think that wiring a house is the same. The problem is that there are code laws out there to protect us from unforseen and misunderstood problems. If you are not aware of these practices - PLEASE contact someone who knows. Like a licenses (but not necessarily union) electrician. If you dont know what your doing, don't. -- =============== regards 'mark ============================================= Mark Ahlenius voice:(708)-632-5346 email: uunet!motcid!ahleniusm Motorola Inc. fax: (708)-632-2413 Arlington, Hts. IL, USA 60004
jad@dayton.UUCP (J. Deters) (01/17/91)
[ Uh oh, here we go again! It's my turn, guys, I saw it first! ]
DANGER, WILL ROBINSON, DANGER.
This idea seems to make it around sci.electronics at least once a year
or so.
+------------------------+
>>>>>>>>>>>>>>>>>>>>>> | NEUTRAL IS NOT GROUND! | <<<<<<<<<<<<<<<<<<<<<<
+------------------------+
> Article <1948@umriscc.isc.umr.edu> From: robf@mcs213k.cs.umr.edu (Rob Fugina)
>In article <kJhTxoE@quack.sac.ca.us> mrapple@quack.sac.ca.us (Nick Sayer) writes:
>>Now ground and neutral clearly are not the same thing. I would
>>expect negative side effects were I foolish enough to hook
>>a light bulb between hot and ground.
[It will work, but you don't want to run it this way]
>Ground and neutral are exactly the same thing. If you were to trace the
>wires back to your breaker box, you would find bare wires (ground) and white
>wires (neutral) both connected to a grounding strip.
Neutral exists as a return path for the current. It is an active part
of the current flow. Ground, on the other hand, is there for safety.
You should never (NEVER) use ground as a designated return path for the
current. Ground exists (for among many other reasons) so that if a
device's insulation fails, there is a safe path for current to return
so that the fuse or circuit breaker can trip. You wouldn't want that
return path to be you...
>MY QUESTION is, if you don't have 3-wire connections in your house, why
>can't you connect the white wire to the ground lug and conuit/boxes, etc???
Have you ever disconnected a piece of conduit that was acting as neutral,
or even touched one while standing on a wet concrete floor? It's unpleasant,
to say the least, and it surprises the hell out of you!
-j
--
J. Deters
INTERNET: jad@dayton.DHDSC.MN.ORG We've changed our location, and
UUCP: ...!bungia!dayton!jad we are now in our new lab. Please
ICBM: 44^58'36"N by 93^16'14"W <-- update your target list accordingly.gaarder@batcomputer.tn.cornell.edu (Steve Gaarder) (01/18/91)
>>MY QUESTION is, if you don't have 3-wire connections in your house, why >>can't you connect the white wire to the ground lug and conuit/boxes, etc??? If you did this, and the neutral wire failed open for any reason, all of the metal parts of 3-prong appliances would become live, not to mention the outlet boxes, etc. Painful. Possibly FATAL. I once lived in an old farmhouse. If you've never seen farmhouse wiring, you don't know what funky wiring means. Farmers are the original do-it- yourselfers; they never hire anyone to do anything they can possibly do themselves. Splices without enclosing boxes, for example, are common. Well, one day I finished up the dishes, pulled the chain to shut off the light, and reached for the faucet to turn off the water. YOW!!!!! Hmmm... light bulb connected between chain & faucet glows to full brightness... I was lucky to be alive. After considerable prowling, I found that the whole kitchen & dining room was wired with romex with a grounding wire. This romex was fed from some romex without a grounding wire. So the grounds were all connected together, and left floating. Then, in TWO SEPARATE outlet boxes, there was a short from the hot to the ground (accidental, not wired that way). So *every* outlet box and grounding prong was live. Steve Gaarder gaarder@theory.tn.cornell.edu ...!cornell!batcomputer!gaarder
steve@nuchat.sccsi.com (Steve Nuchia) (01/18/91)
In article <896@wells.UUCP> k3tx@wells.UUCP (Dave Heller) writes: >And, really, most of this [damage] is traceable to the Do-It-Youself-ers >and the lower levels of self-defined professionals. ... >I don't like the idea of the d-i-y doing his own house wiring or >repairs even with cookbook in hand. I've seen too many bad, and >some VERY bad results. This was an amplification to a comment I had made, but I'm not sure I completely agree with the radical position. A generally competent do-it-yourselfer should be able to follow a good example safely for the most common types of branch circuits. The bad results I have seen have been the result of corner-cutting -- using the wrong size wire, passing cable through knock-outs without clamps, splicing or tapping without benefit of box, and overloading existing circuits rather than running a new one. With a dose of humility and a willingness to follow even those rules he doesn't understand the d-i-y can be safe. The problem is some of them don't even stop to wonder what the rules are. -- Steve Nuchia South Coast Computing Services (713) 964-2462 "Could we find tools that would teach their own use, we should have discovered something truly beyond price." Socrates, in Plato's Republic