cl2kw@sdcc12.UUCP (06/06/87)
What are the potential effects of a neutral- ground short? While troubleshooting a problem with a PC regularly loosing its Ethernet connection, I identified several 117 VAC outlets on the circuit with neutral-ground shorts. The PC and the network interface card check out ok independently. Could the ground fault be the culprit? Could a flakey device being turned off upstream on the circuit cause the ground fault to exibit its symptoms in the abortion of the network connection? Advanced thanks for any suggestions/answers, Kevin Walsh UCSD Library Systems ...sdcsvax/sdcc12/cl2kw
rmrin@inuxh.UUCP (06/08/87)
> > What are the potential effects of a neutral- > ground short? While troubleshooting a problem with > a PC regularly loosing its Ethernet connection, I > identified several 117 VAC outlets on the circuit > with neutral-ground shorts. The PC and the network > interface card check out ok independently. > Could the ground fault be the culprit? Could > a flakey device being turned off upstream on > the circuit cause the ground fault to exibit > its symptoms in the abortion of the network connection? > > Advanced thanks for any suggestions/answers, > Kevin Walsh > UCSD Library Systems > ...sdcsvax/sdcc12/cl2kw Neutral and ground should be tied together. Look out for the outlets in which it isn't.
grr@cbmvax.cbm.UUCP (George Robbins) (06/09/87)
In article <583@inuxh.UUCP> rmrin@inuxh.UUCP (D Rickert) writes: > > Neutral and ground should be tied together. Look out for the outlets > in which it isn't. Neutral and ground should be tied together *** at or near the fusebox ***. Having them tied together at the outlet is wrong and a good indiction that you should look for more questionable and dangerous wiring practices. -- George Robbins - now working for, uucp: {ihnp4|seismo|rutgers}!cbmvax!grr but no way officially representing arpa: cbmvax!grr@seismo.css.GOV Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
baldwin@rochester.ARPA (Douglas Baldwin) (06/09/87)
In article <583@inuxh.UUCP>, rmrin@inuxh.UUCP (D Rickert) writes: > Neutral and ground should be tied together. Look out for the outlets > in which it isn't. Not according to standard electrical codes - for instance, the National Electrical Code requires neutral and ground conductors to be SEPARATE, with the ONLY connection between them being a single point at the service entrance. I think the idea is to make sure the ground conductor doesn't carry any significant current, thus avoiding noticeable voltage drops along it, thus making sure that it really is at ground potential everywhere. (I suppose a large enough voltage difference between different "ground" points could explain the original poster's problems....)
wtm@neoucom.UUCP (Bill Mayhew) (06/10/87)
It is difficult to troubleshoot the ethernet problem without a some more detailed information. The co-ax cable for the ethernet system should only be attached to an earth ground at a single point on the cable. Being grounded at only one location prevents currents from circulating in the shield of the cable and thus inducing noise. Normally, the transciever units that tap the cable are optically and/or transformer isolated to prevent multiple grounds from being formed. I`d suspect that if the interface you have has a transciever box that clamps on the cable, that there is something wrong with the cable that connects the interface with the cable tap transciever. Carefully check that the cable shield is intact. Most of the problems that I have seen are caused by a problem in the cable between the interface and the transciever tap module. One last idea is to make sure that the box on the cable tap transciever is properly put together. Sometimes nylon screws and washers, etc. are used to prevent a ground from being fromed inadverntantly between the ethernet cable and the PC. Hope this gives you some ideas... Bill NEOUCOM Division of Basic Medical Sciences (wtm@neoucom.UUCP)
larry@kitty.UUCP (06/11/87)
In article <1989@cbmvax.cbmvax.cbm.UUCP>, grr@cbmvax.cbm.UUCP (George Robbins) writes: > > Neutral and ground should be tied together. Look out for the outlets > > in which it isn't. > > Neutral and ground should be tied together *** at or near the fusebox ***. > Having them tied together at the outlet is wrong and a good indiction that > you should look for more questionable and dangerous wiring practices. The National Electrical Code (section 250-23) makes it clear that the current-carrying neutral and the earth ground wires should be bonded at one and ONLY ONE place in any electrical system: the service entrance panel (i.e., main disconnect) immediately following the meter. There are several reasons for this: 1. An open or high-impedance (i.e., faulty) neutral line in the building distribution wiring, coupled with a high-impedance (i.e., faulty) equipment ground (like poor conduit bond) could result in dangerous voltages present on the earth grounds of interior wiring. 2. Ground loops can exist in that some of the equipment (i.e., earth) ground wiring will be carrying current under normal conditions, thereby resulting in equipment grounds being at other than zero potential. 3. The result of (2) above can cause significance interference with data communications equipment. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
news@rlvd.UUCP (06/12/87)
In article <583@inuxh.UUCP> rmrin@inuxh.UUCP (D Rickert) writes: > >Neutral and ground should be tied together. Look out for the outlets >in which it isn't. Neutral and ground should NEVER be tied together. Ask yourself what is the point of having seperate lines if you are going to join them together. The reasons for keeping them separate are to do with the safety of the earth protection in the event of a Neutral fault. The short is liable to cause problems since there will be earth currents as the result, since Neutral is (almost)never at zero potential. Disclaimer- My experience relates to UK practice but I cannot imagine any reason why the US should be different. However if you dont know this problem in detail then I suggest you should seek expert advice before altering anything. Martin Loach UK JANET: mjl@uk.ac.rl.pyr-a ECF User Support, Informatics Division Amateur Radio: G8UDJ Rutherford Appleton Labs Chilton Didcot Oxon Why am I here? OX11 0QX I should have stuck to being a lumberjack.
psfales@ihlpe.ATT.COM (Pete Fales) (06/17/87)
In article <467@rlvd.UUCP>, news@rlvd.UUCP (News) writes: > In article <583@inuxh.UUCP> rmrin@inuxh.UUCP (D Rickert) writes: > > > >Neutral and ground should be tied together. Look out for the outlets > >in which it isn't. > > Neutral and ground should NEVER be tied together. Ask yourself what is the > point of having seperate lines if you are going to join them > together. The reasons for keeping them separate are to do with the > safety of the earth protection in the event of a Neutral fault. I think that part of the confusion here is that no one has ever defined what they mean by "tied together." If what you mean is "visibly connected with a wire" then, as previously stated, it is imperative that they be connected only at the service entrance. However, I suspect that the D Rickert and the original poster meant that AFTER DISCONNECTING THE MAIN CIRCUIT BREAKER, if you check neutral and ground with a ohmmeter, you will find them shorted together. In this case, you should worry if they aren't connected because the neutral is not providing you with any protection. -- Peter Fales UUCP: ...ihnp4!ihlpe!psfales work: (312) 979-7784 AT&T Information Systems, IW 1Z-243 1100 E. Warrenville Rd., IL 60566
collinge@uvicctr.UUCP (Doug Collinge) (06/20/87)
In article <467@rlvd.UUCP> mjl@pyr-a.UUCP (Martin Loach) writes: >In article <583@inuxh.UUCP> rmrin@inuxh.UUCP (D Rickert) writes: >> >>Neutral and ground should be tied together. >Neutral and ground should NEVER be tied together. What I have wanted to know for years is, why is residential service referred to ground at all? I understand why they balance and ground high-voltage transmission lines. It seems to me that, if the transformer was used to isolate the residential service from ground everyone would be a lot safer. How about it? -- Doug Collinge School of Music, University of Victoria, PO Box 1700, Victoria, B.C., Canada, V8W 2Y2 collinge@uvunix.BITNET decvax!uw-beaver!uvicctr!collinge ubc-vision!uvicctr!collinge
dsi@unccvax.UUCP (DataSpan R+D) (06/22/87)
In article <258@uvicctr.UUCP>, collinge@uvicctr.UUCP (Doug Collinge) writes: > What I have wanted to know for years is, why is residential service > referred to ground at all? I understand why they balance and ground > high-voltage transmission lines. It seems to me that, if the transformer > was used to isolate the residential service from ground everyone would I for one would much prefer the service coming into my home to be referenced to earth ground. As an engineer who (occasionally) builds broadcasting stations, I can assure you that the effects of lightning strikes are swift and dramatic. If the distribution system in the home were left in an essentially floating, balanced line condition, the danger of electrocution due to leakage from L1-L2 to a cold water pipe (say, the poorly designed toaster in the kitchen) would be minimized. The danger from fire due to extremely high voltage transients would not be minimized. It is much easier to insulate 240 VAC than a few million volts of very high current pulses from a dwelling and its occupants. Pole transformers (which actually have the secondary windings isolated, but the center tap is grounded to the case *at the pole*) would probably get internal shorts anyway just as soon as a service drop was hit, which would negate any of the advantages of balanced line operation. Increasing the insulation required for this service would drop transformer efficiency. The best solution are ground fault interrupters, in conjunction wiht the present system in use. David Anthony DataSpan, Inc
ron@topaz.rutgers.edu (Ron Natalie) (06/23/87)
It wouldn't even take lightning strokes, just passing clouds to induce enough static charge to arc accross the conductors. Lightning rods do more than attrack strokes to a benign place, they dispell charges that would cause arcs to form. -Ron
les@celerity.UUCP (Les Merrill) (06/23/87)
>What I have wanted to know for years is, why is residential service >referred to ground at all? I understand why they balance and ground >high-voltage transmission lines. It seems to me that, if the transformer >was used to isolate the residential service from ground everyone would >be a lot safer. How about it? Safety is best when the transformer is center-tapped and grounded at the utility pole. A totally ungrounded circuit is subject to accidental connection to dangerous voltages with no warnings available. Center- tapping is the way they do it, except that the basic supply voltage is 220 v. balanced to ground/neutral. You plug into one half of the supply when you use the common residential outlet. The notion of one-side-is-ground hails back to the beginnings of everything. There was a Samuel F. B. Morse who had something to do with a single-ended telegraph circuit between Washington and Baltimore (or was it Piladelphia ?) where the earth really WAS the other side of the circuit.. --les bigbang!celerity!les
levy@ttrdc.UUCP (Daniel R. Levy) (06/24/87)
In article <258@uvicctr.UUCP>, collinge@uvicctr.UUCP (Doug Collinge) writes: > What I have wanted to know for years is, why is residential service > referred to ground at all? I understand why they balance and ground > high-voltage transmission lines. It seems to me that, if the transformer > was used to isolate the residential service from ground everyone would > be a lot safer. How about it? I think the idea is that, with the common household 240-volt service (two 120-volt sides on the power transformer secondary with a tie point in between that is grounded) the center point being deliberately grounded prevents the worst case voltage to ground in the system from being any higher than 120 volts. Otherwise, if one side of the 240 became acci- dentally grounded, the other side would be (unexpectedly) 240 volts with respect to ground and would pose a (much) worse shock hazard than 120 volts. As it is, if either side of the 240 becomes accidentally grounded, a fuse blows or a circuit breaker trips instead, alerting one to the problem and causing no unexpected shock hazard. (I saw this in a rather old elementary electricity handbook, so this may or may not be on the level. But it sort of makes sense, in that an insid- ious shock hazard due to a short to ground could occur and never be detec- ted until some unfortunate person found himself between the other side of the 240 and ground.) I suppose another problem would be that of controlling the maximum DC voltage on the secondary side with respect to ground, to prevent insulation breakdown in the transformer or for that matter in any equipment serviced by the transformer which has a grounded case. Even static electricity could become a problem. -- |------------dan levy------------| Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa, | an engihacker @ | vax135}!ttrdc!ttrda!levy | at&t data systems division | Disclaimer: try datclaimer. |--------skokie, illinois--------|
collinge@uvicctr.UUCP (Doug Collinge) (06/24/87)
In article <753@unccvax.UUCP> dsi@unccvax.UUCP (DataSpan R+D) writes: >In article <258@uvicctr.UUCP>, collinge@uvicctr.UUCP (Doug Collinge) writes: >> What I have wanted to know for years is, why is residential service >> referred to ground at all? > If the distribution system in the home >were left in an essentially floating, balanced line condition, the danger >of electrocution due to leakage from L1-L2 to a cold water pipe (say, the >poorly designed toaster in the kitchen) would be minimized. The danger >from fire due to extremely high voltage transients would not be minimized. >It is much easier to insulate 240 VAC than a few million volts of very >high current pulses from a dwelling and its occupants. OK, I get your drift - but telephone companies run floating lines into houses and solve the lightning problem with surge arrestors. Why can't the power company put surge arrestors in the transformers and/or in the house? Yes, and Ground Fault Interruptors are wonderful, of course. -- Doug Collinge School of Music, University of Victoria, PO Box 1700, Victoria, B.C., Canada, V8W 2Y2 collinge@uvunix.BITNET decvax!uw-beaver!uvicctr!collinge ubc-vision!uvicctr!collinge
ken@rochester.arpa (Ken Yap) (06/24/87)
|OK, I get your drift - but telephone companies run floating lines into |houses and solve the lightning problem with surge arrestors. Why can't |the power company put surge arrestors in the transformers and/or in the |house? Yes, but the telephone company doesn't have to worry about connections that get wired up to all the electrical appliances in the house. I think capacitive transfer will probably raise the potential of the ground wire should the power line get a direct hit, making all grounded frames, like fridges, live. I remember a page in the phone book, where I grew up, warning against using the phone in a thunderstorm. Wonder if they still have that page. Ken
larry@kitty.UUCP (Larry Lippman) (06/26/87)
In article <1781@ttrdc.UUCP>, levy@ttrdc.UUCP (Daniel R. Levy) writes: > > What I have wanted to know for years is, why is residential service > > referred to ground at all? I understand why they balance and ground > > high-voltage transmission lines. It seems to me that, if the transformer > > was used to isolate the residential service from ground everyone would > > be a lot safer. How about it? > > I suppose another problem would be that of controlling the maximum DC voltage > on the secondary side with respect to ground, to prevent insulation > breakdown in the transformer or for that matter in any equipment serviced > by the transformer which has a grounded case. Even static electricity > could become a problem. Dan Levy hit the nail on the head: the most fundamental reason for grounding the secondary of an AC power distribution transformer is to ensure that any primary (i.e., high-voltage side) to secondary transformer winding fault will be of sufficient current magnitude to trip the primary side overcurrent device (i.e., high-voltage fuse). Transformer faults involving primary to secondary conduction are not uncommon, especially in transformers which are subject to overload and thereby overheat, consequently stressing the dielectric oil and the winding insulation (often paper). Needless to say, if the secondary were ungrounded, a primary to secondary fault could result in not only lethal voltages present on all interior building wiring, but would most likely cause a fire through insulation breakdown and subsequent arcing. The trend today is for electrical utilities to switch to higher distribution voltages feeding customer distribution transformers. The traditional 4160/2400 volt wye distribution is being replaced by 13200/7600 volt service. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
henry@utzoo.UUCP (Henry Spencer) (06/26/87)
> ... the telephone company doesn't have to worry about connections > that get wired up to all the electrical appliances in the house... Yup, and the phone company goes in heavily for plastic construction. On a standard phone, unless you reach underneath for the base plate, the only metal part you can touch is the dial stop, which is (I think) isolated from the working parts inside. Note also that different standards apply, to some extent. The phone system is not UL-approved and never will be, barring the day when everything is done with fiber optics instead of wires. (The high ringing voltages cannot be reconciled with UL standards, I'm told.) -- "There is only one spacefaring Henry Spencer @ U of Toronto Zoology nation on Earth today, comrade." {allegra,ihnp4,decvax,pyramid}!utzoo!henry