This is very informative issue of the EMUSIC-D list, concerning AC grounding problems and their solutions. ================================================================================ Reply-To: Electronic Music Digest Sender: Electronic Music Digest From: Joe McMahon Subject: EMUSIC-L LOG9101E A1 To: Multiple recipients of list EMUSIC-D EMUSIC-L Digest Volume 36, Number 5 This issue's topic: Fight the (AC) Power Your EMUSIC-L moderator is Joe McMahon. Please send articles to EMUSIC-L@AUVM.BITNET. Send administrative mail to xrjdm@scfvm.gsfc.nasa.gov. Digests are distributed as discussions finish. For faster response to questions,subscribe to EMUSIC-L at LISTSERV@AUVM.BITNET. Subscribers to this list may send mail to EMUSIC-D; it will be forwarded to EMUSIC-L. Back issues are available from xrjdm@scfvm.gsfc.nasa.gov. Anonymous FTP may be available soon. ------------------------------------------------------------- Date: Thu, 10 Jan 91 12:47:00 EDT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: "William R(ay) Brohinsky" Subject: Grounding (was: Re: Team Metlay, continued: Networking Considerat Interesting that you folks should have pegged safety as first priority: I have been involved in a (sometimes heated) discussion on BIX concerning noise between a Mac and the user's stereo. Someone suggested that it was ground-loop induced (I asked for, but never recieved, a better description of the noise, but everyone seems to have decided it is ground-loop induced!) The first `do this' response involved using a third-wire-breaking adaptor to eliminate the case ground connection on the mac. I responded with an impassioned plea for safety, and the response was somewhat amazing: roughly 2/3 of the comments (an admittedly small sample) were in favor of safety first, and 1/3 felt that I was over cautious and even wrong to raise such concerns. I hope it is common knowledge, but 30V can kill! Real, honest to goodness Dead! Is this fact being taught to our up-and-coming E-musicians at the schools? I hope so... I applaud Team Metlay for their sensible priorities. I personally would prefer to see a session fail to produce a salable result to seeing any on [of] the players/techs get hurt. (maybe not good economics, but it isn't necessary for this choice to even come up with a modicum of planning!) For my part, I always tree my power. I find the power strips from Radio Shack to be just fine, and they had the added bene that, when the wind and a tree branch knocked the neutral line off my house, but left the hot line attatched, the GE-movs in the strip box fried, and protected my computer and synths! (also, my TV, VCR, Stereo, etc. I use a lot of them...) GFI's tend to trip if there's a 5ma difference between the current flowing in the hot and neutral lines. When a person is sweaty, and in a certain mood, his/her internal resistance can get as low as 600 ohms. 10ma of current through a person's chest will kill them. 5ma MAY kill them--- it isn't like 9ma won't but 10ma will! 120V can be lethal. Team Metlay were probably safer by knowing their systems and maintaining good power and case grounds than they would have been relying on the GFI! `Know your equipment, and thyself,' said he, Peloniusly. [forgive the spelling...] raybro ------------------------------------------------------------- Date: Fri, 11 Jan 91 10:22:48 GMT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: Nick Rothwell Subject: Re: Grounding >For my part, I always tree my power. Me too. I don't know how mains power is wired in houses in the US, but in the UK all the wall sockets in any room (each socket rated at 13A) are wired to a ring main, which can carry 30A; each socket therefore has two circuits to the source. I had a huge amount of mains hum when my studio was rebuilt after the Electronica gig. I've just rebuilt it again, running practically everything out of a single socket, and it's fine. Using several sockets on a ring main means that you've got ground loops around the walls of the room - not too good, I feel. When I arrived in the US and we started assembling the Team Metlay Technorubble, you know what surprised me the most? Answer: some of the absolute sh*t that people in the US draw 110V out of. Wall sockets are just cheap plastic boxes with a couple of slits and bits of brass - no shuttering on the slits or anything. Extension blocks are often cheap bits of plastic with holes punched through them. Earthing (grounding) seems to be pretty much a secondary concern ("no problem, I'll just attach it to this screw here..."), and half the sockets don't accomodate earth pins. Since the US runs at 110V rather than 240V, the voltage is less dangerous (marginally...) but there's twice the current and hence twice the risk of overheating. In the UK, plugs and extension sockets are big and bulky, but seem a lot more solid. I've just rewired all my racks for mains power with a switch on the front of each rack and an internal cooling fan ("whirrrr"), and I went over the things with a fine-toothed multimeter to make sure the connections were solid. I still have to install GFI's and surge suppression, although I can't decide whether to do this for each rack individually or have a master distribution box. Nick. ------------------------------------------------------------- Date: Fri, 11 Jan 91 10:27:00 EDT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: CHRIS@FANDMA.BITNET Subject: Grounding question This discussion of the Team Metlay setup reminded me of a wierd statement I heard recently. A couple of the guys in the band I'm in were discussing buzz and hum in the PA system, and one of the guys said he thought the system was "over-grounded" (apparently meaning we had to many pieces of equipment on the same common ground, or some such notion), and that by *lifting the ground at the wall outlet for the entire system* we would get rid of the noise. To me this sounded like a recipe for death and destruction of equipment, but I didn't have enough information to sway this guy's arguement. Has anyone on the list ever heard of a condition called "over-grounding", and if so, care to elaborate on it? I suspect that lifting the ground *would* get rid of the noise, but I personally would be afraid to touch any of the equipment once that was done. -chris ------------------------------------------------------------- Date: Fri, 11 Jan 91 15:58:47 EST Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: ronin Subject: overgrounding 'too much ground' usually means that the system is going to ground at two differnt places, with different floating ground references. when assembling an ac network, one wants as much as possible to pull all the grounds to the same place, and spike it to earth, so that all the divices see the same ground reference. otherwise, there is a danger of hum. lifting the third prong removes an extra reference from a machine that is already trying to ground itself by another path, usually the audio lines to the patch bay/mixer. unless the thing has that ac ground connection wired to its external casing, you're usually pretty safe doing this. remember, electric shock occurs when your body provides a current path to a circuit. ----------< Extremism In The Pursuit Of Good Noise Is No Vice >---------- Eric Harnden (Ronin) | V.P., Chief Engineer | Transmedia Music, inc. The American University Physics Dept.| (202) 347-8050 Washington, D.C | ------------------------------------------------------------- Date: Fri, 11 Jan 91 13:44:00 EDT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: METLAY@PITTVMS.BITNET Subject: Re: Grounding question That's a weird term for a ground loop, which is essentially what he's describing: more than one path to ground for all signals. I do NOT recommend lifting the ground at the wall! If you have a bass amp set up near you with the polarity switch set wrong, and you put on the bass and mute the strings and then touch a mic that's wired to the house PA to see if it's on-- well, let's just say that's why Uriah Heep had to audition a new bassist somne years back. There are safer ways to kill ground loops: cheater plugs at the source are stupid and dangerous. metlay ------------------------------------------------------------- Date: Fri, 11 Jan 91 13:03:00 EDT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: "William R(ay) Brohinsky" Subject: Re: Grounding question By the way: I've never heard of over-grounding either. An alternative to treeing your power connections: get a 40' roll of 3/4" braid, usually tinned copper. Also get a set of two lugs for each piece of electrical equipment large enough to hold the braid. Cut lengths of braid to go from an 8' copper pole that is driven into the ground to each piece of equipment and crimp a lug at each end. Bolt one end of each braid to the rod, and drill a hole in each piece of equipment. Use a wire brush (one of those that mount up in a power drill works very nicely!) and remove all of the paint for a 1/2" radius beyond the hole, and bolt the other lug to it. This hole should be as close as possible to the green wire connection inside of the equipment. Now, all equipment will be at very near the same potential! This worked just fine for a 10joule laser that was arcing between it's cabinets. It should work just fine for your next live E-music setup. It's also much more expensive than sensible routing of power lines in the first place, and lowers the resale value of the equipment. But it's lots safer than lifting the ground at the wall for the whole system! raybro (in a more brief mode) ------------------------------------------------------------- Date: Fri, 11 Jan 91 11:41:00 EDT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: "William R(ay) Brohinsky" Subject: Re: Grounding question Chris, Grounds are there for a reason. They come in two types, signal and power, but both types serve the same purpose: to provide a return path for the current that flows out of a current source. (note that a voltage source is also a current source: one names the potential (volts) to make current flow, the other names the measure of current motion (amps).) Ground loops happen when more than one ground path is available. Normally, a musician sees a ground loop when he has his instrument plugged into an amp (through a signal cable) and both instrument and amp have power cords which have ground lines that are common to the signal ground. Because 60Hz (50Hz in England) is such a low frequency, filter capacitors must be MASSIVE to be large enough to successfully remove AC from DC power lines in the instrument and amp circuits. This AC is normally shunted to ground. That means that it manifests itself in the (normally negligable) resistance of the return line. When the return line becomes resistive (which any real wire is, regardless of its diameter!) then a noise voltage representing the ac becomes available. Speaking JUST of power for the moment: Normally, there are 3 lines on a power connection. One is called HOT, one is called NEUTRAL. These are the _normal_ current carrying paths for the power supplies in instruments and amps. Hot is generally attached to the power source (one of the three phases from the power transformer) and the other is generally attached to `ground' in the form of a rod driven into the earth near your home. In my case, the rod is ~1/2inch thick, and 6-10 feet into the ground. The neutral line is also attached to one of the three phases from the transformer (a different one, so that you get a voltage difference between them, of course). If that ground lifts, i.e., some rodent chews through the wire connecting the fuse/breaker box neutral to the earth-rod, then the neutral side may appear to be at some voltage well above ground potential. Since your pipes tend to be metal and tend to run into the ground sooner or later, this is a life threatening problem: cross neutral to a pipe and fry! To reduce this kind of problem aboard ships of the US navy, the `HOT' and `Neutral' lines are 55volts, out of phase with each other. That way, there is 110v (nominal) between the two lines, but either one is only 55v above the voltage of the metal ship, reducing by 2 (by 4 if you consider power) the damage from a short. The damage can still be miserably bad... Once upon a time, in the US, there were only these two connections to power: hot and neutral. The metal case of, say, an appliance, would be unconnected, for safety. Unfortunately, if a heating element broke (the most common occurance, although worn insulation was a pretty common problem, too) it would tend to contact the case (being usually spring-shaped). Then, the case would be connected to hot, or neutral. Depending on the side connected (or the potential in any case) this could be dangerous. If your toster connected its case to hot, and the coffee maker connected to neutral,and you tried to move both of them at once... So NEC (the national electrical code) and UL (the underwriter's laboratory) and some other safety agencies decided to catch us up with the rest of the world. Hence, the green wire. This is truely the GROUND. Whereas the neutral can float above ground potential (as it surely does aboard ship) the ground pin MUST be a good connection to ground. An appliance/instrument/amp with a 3-prong plug will have its case attatched to the green wire, which attaches to this good ground through the third (round) prong. Now, if the element breaks, the case remains at ground potential, and all that current that could have run through you runs to ground. Yes, that may destroy things in a red- hot spray of sparks, but at least you aren't likely to be attached to it... As for signals: you usually have a signal line and a ground line. The ground may be wrapped around the signal or braided around it to provide some shielding. This is so that the ground will absorb any RF interference, and carry it off before the amp gets it. (If you hear radio stations from your speakers, check both the grounds and the quality of the signal connections. but we won't get into radio recievers from dissimilar metal connections here...) Normally, both signal and ground are connected at both ends to the signal output and ground at the instrument end, and likewise the signal input and ground at the amp end. A normal signal will travel from the instrument to the amp on the signal wire, and the return path is through the ground wire. If, however, there is another path for the ground return, you can get effects in the amp you don't want. [let me correct an earlier statement: the grounded shield blocks RF from the signal wire, usually, rather than `carrying it off' anywhere] Current flows through loops. The signal-ground return forms such a loop. If the signal ground is connected to the power ground (neutral) or the case ground (3rd prong) at both the amp and inst, then signal current can flow in the same wires that power noise is being carried off. This is the canonical ground loop. Another mechanism here (maybe even the more effective for causing troubles) is that current from the power supply ground can actually travel through the signal ground, and cause the potential difference between the signal ground and signal wire to change at 60Hz. The amplifier will amplify this difference, and hum (or if it gets distorted, buzz) comes out! The canonical fix among the incognoscenti is to break the third prong connection. This MAY break the ground loop! It certainly will reduce a level of safety in the equipment, and may cause effects from mild finger-buzzies when you touch your guitar strings or synth case to death. The canonical fix among techs who have worked in data acquisition is to lift the signal ground at the instrument input. This breaks the ground loop for the signal, while allowing ground return through the power connections. Note, that when you use this cable with a system that doesn't suffer from a ground loop, or one that doesn't have power-grounds inter- connected, you won't get any sound out of the system. That solution may be ok for DA, but I've never liked it for music: too much chance of using a knackered cable somewhere else. Very frustrating. So lets look at the actual cause of the noise: When you have a power connection, and you use power, current flows in the ground return. It will tend to take the path of least resistance. The more power you use, the more current flows. Since the ground is largely made of cable and wire, the fact that wire has a finite resistance couples with the current flow to produce a voltage, which can be measured. From one end of the ground path to the transformer, you may measure less than half of a volt. Not much, compared to 120V, but what happens when that .5 volt gets to the input of your 1v-input amp? You guessed. Power ground loops happen when the ground of system one is connected at one point in that ground return, drawing lots of current, and system two gets connected down stream from it. The grounds for the two systems will be at different potentials, depending on the current and resistance in the wires from sys1 to sys2. That voltage would cause a current to flow between sys1 and sys2 if you connected their grounds through another wire, say the signal ground... Now you have a ground loop that is causing hum. You can break the ground at sys1 in the signal wire, and there is still a ground return path. There is also all that hum current in that path: if the amp is sensitive, that current will get picked up and amplified. You've reduced the hum, but not eliminated it. ENTER THE TREE: If you ensure that both sys1 and sys2 are plugged into power VERY closely, then you can be pretty sure that any ground loops you make will not have current flowing in them (or at least not enough to worry you). SO, it is a good idea to take a multi-plug box where you are sure that all the plug connections are good, and all plugs are within a small area, and use that to plug an instrument, it's controllers and effects, and amp into. Hence the name tree: a trunk with branches. raybro ------------------------------------------------------------- Date: Mon, 14 Jan 91 11:01:45 GMT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: Nick Rothwell Subject: Re: Grounding question >ENTER THE TREE: >If you ensure that both sys1 and sys2 are plugged into power VERY closely, >then you can be pretty sure that any ground loops you make will not >have current flowing in them (or at least not enough to worry you). I can verify that this approach works. I pretty well eliminated the ground hum from my setup by rewiring each of my racks for mains and running practically everything from a single socket. The hum is extremely low indeed (even though the racks have cooling fans wired and running), and everything is properly earthed. Don't cut your earth connections. Just say no. Nick. ------------------------------------------------------------- Date: Sat, 12 Jan 91 15:51:30 EST Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: Jeffrey R Kell Subject: Re: Grounding question In-Reply-To: Message of Fri, 11 Jan 91 11:41:00 EDT from No wait a minute; Raybro mentioned a HOT and NEUTRAL side, but the neutral does NOT have a current potential with respect to ground. The "three sides of the transformer" approach is typical 3-phase wiring, but uncommon for home use. Three-phase 240v, for example, gives you 240v net in a 3-phase motor; the voltage between any phase and ground (neutral) is 120v, and between any two phases around 208v. Home wiring is true two-phase, each leg being 180 degrees out of phase with the other (as opposed to 3-phase, where they are 120 degrees out). Home wiring involves three wires to your house (count 'em if you're skeptical). Two are "hot" and the third neutral. The voltage potential between either hot side and neutral is 110-120v. The voltage potential between the two hot sides is 220-240v. The situation Ray mentioned about case grounds is true, and the same as what I described earlier; but the neutral is truly neutral with respect to ground (well, there is often a small voltage potential, but it ain't hot). And he was equally correct in that you often ended up swapping neutral/hot from the intended sides, especially with old 2-prong non-polarized plugs. The first quick-fix was the polarized plug (that's why one prong is "fatter" than the other) and the final fix was the addition of the ground wire (green) which is supposed to go to a true, honest-to-goodness earth ground at the electrical service entrance rather than relying on the service ground (neutral) connection. The problems continue to this day... our latest computer equipment installed required 3-phase power on a 5-wire circuit - 3 hot phases, 1 neutral, 1 earth ground, and a max 5v potential between neutral and ground. The ground is there as a fail-safe for the neutral (in all applications). If a rat gnaws through your hot wire, you're safe (but out of power). If its the neutral, then the current seeks out an alternate ground. ------------------------------------------------------------- Date: Fri, 11 Jan 91 11:37:18 EST Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: Jeffrey R Kell Subject: Re: Grounding question In-Reply-To: Message of Fri, 11 Jan 91 10:27:00 EDT from Okey dokey... electronics 101 :-) The big deal here is that with ordinary 110-volt power, one prong is "hot" and the other prong is "neutral" (and the extra one you broke off should be a ground) :-) In many applications, you have a chassis ground (hopefully neutral) since it makes for a cheap, easily wired system. If you touch the case and also touch ground, it won't fry you (yet) since the case is the neutral side. But then Murphy's law strikes, something goes wrong, and what can happen? * If the neutral side is shorted, the current will now seek you out as a ground and you get fried. Thus the invention of the ground wire, its a secondary neutral. * If you're playing around with plugs, you might plug it in backwards (which can be done easily enough without the ground wire). Now the case is hot, but no damage yet since the neutral is still intact. But if you touch another case with a proper plug (and neutral case) then fzzztttt... * If the building is wired for 220v then individual outlets may be on different phases (ie, for 220v you go hot-to-hot between two sides of opposing polarity). If you screw up as above you might get 220v instead of 110v, and it will *greatly prefer* you over the ground. * This 220v differential phasing is what creates ground loops. If you complete a path between grounds of *opposing* phases, you get induced eddy currents and RF fields (and a nasty 60Hz buzz). The idea is to have *everything* on a *common* ground, fed by a *common* phase of current. It doesn't *have* to all come from one outlet (if you are damned sure how and how *well* they are wired) but that's one way to be sure. And everything should be in phase. If you lift a ground you can avoid some of the ground-loop problem, but you have to be real sure there's a good ground in the overall system. I have heard recommendations to pull grounds on everything except the power amps; while this usually works, and is theoretically sound, it still isn't all that safe. If you have a ground fault, you still leave a prettly long path to ground, and you might end up well done. /Jeff/ ------------------------------------------------------------- Date: Mon, 14 Jan 91 11:39:00 EDT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: "William R(ay) Brohinsky" Subject: Re: Grounding question Jeffry Kell is quite right that home wiring is not true three phase, and almost right in that the neutral `does not have a current potential with respect to ground'. I apologize for the misstatement: my experience has been as an ET, both onboard a ship, and as a civilian for both military and industry. Since I am not always intimately focused on the power mains, I do sometimes cross the two experiences: in civilian and industrial life, the 110v line is often 117-120 volts and the neutral is supposed to be really neutral to ground. On a US navy ship, the two lines are both `hot', but there is SUPPOSED to be no connection between the generator and the ship's metal structures: hence, both sides do `not have a current potential with respect to ground'. We were always warned not to screw with safety/case grounds, though, because it was ALWAYS possible that the connection could be there. In the Nav, the possibility comes with emergancy, war, or any occurance that can shake up or damage a ship. At home, the proverbial rat in the conduit will suffice! Still and all, it boils down to this: don't mess with the green wire! raybro ------------------------------------------------------------- Date: Mon, 14 Jan 91 13:49:00 EDT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: CHRIS@FANDMA.BITNET Subject: Another grounding question Many thanks to all who responded to my question on grounding, especially Jeff and Raybro who went above and beyond the call of duty. I understand the tree design, but in my case it's not practical: we have three 800-watt amps driving the main PA and another 800-watt amp driving the monitors, in addition to two guitar amps, a bass amp, a keyboard amp and the rest of my keyboard setup all on stage. I doubt that we could drive all of that off one circuit. Even if we could, there's still the mixing board to power up, which is at the end of a 300 foot snake on the other side of the room. So, if a tree layout isn't viable, what's a poor e-musician to do? -chris ------------------------------------------------------------- Date: Mon, 14 Jan 91 14:28:00 EDT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: "William R(ay) Brohinsky" Subject: Re: Another grounding question Chris, yours is one of the systems that calls for the 3/4" braid! The idea is to get the lowest resistance cable possible (preferably insulated) and to make a `power snake'. Since the mixing board is not the highest current user, I would put all of the local plugs at the stage, and then run a special power hookup for the mixer. You should first have ONE person in the group (or with the roadies) who is responsible for power, and that one person only should be authorized to plug things in. He should also have a backup, unless the band can't play without him. This one person has to be able to use a multimeter, as a minimum. Some training in electronics is desirable, so your sound man should make a good first choice. When you arrive on site, he should ensure that there are two 30-amp services available (it should actually be arranged before arriving:-), and he should make measurements on the grounds to ensure that they do not have a resistance between the two services. (allowable is well under .1 ohm). He should have a power snake that consists of the following: -two three prong plugs, whose grounds are connected thru the low-resistance cable, which also connect to two power-distribution centers. The PDC's should be able to be placed onstage far enough apart to provide power to everything. The ground cable between the plugs must be long enough to stretch between the services. One of the three-prong plugs should also have ...actually, a picture may be better: || || L/ L/ | plug for one service | plug for other service |\________________________/|\ | 3/4" braid, jacketed | \ | | \ | | \ | power lines (3-cond) | \ | to PDC's (30-amps max) | \ | | | 3-conductor cable (5-amp) with | | | 3/4" braid(jacketed) ground | | | -------- ---------- | | | | | | | | PDC's (2) with | | | | | enough plugs for| | | | | stage equipment | | | -------- ---------- | | | long enough cable to reach to rear | of room (same length as snake + | power lines) | | / \ L__| plug for mixer Use hospital-grade (with the green dot) plugs and jacks, and don't be afraid to spend what it takes to do it right. Don't use the green wires in the 3-conductor cables (and make sure that the cable you use will handly [handle] 30 amps!) and either have an electrician build it or at least have one check it. This will ensure a few things: first off, you will have one person, at least, in the group who understands ground loops, and you will have a mechanism ready to avoid them. Second off, you will have ensured that your power distribution problems are limited to what the site offers, and you won't introduce any yourself. Third, by adding breakers to the distribution boxes, you may be able to avoid plunging the room into darkness... This is a drastic solution, but one that will guarantee a minimum of danger for the players, and a minimum of hum. raybro ------------------------------------------------------------- Date: Mon, 14 Jan 91 15:27:23 EST Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: Jeffrey R Kell Subject: Re: Another grounding question In-Reply-To: Message of Mon, 14 Jan 91 13:49:00 EDT from On Mon, 14 Jan 91 13:49:00 EDT said: >I understand the tree design, but in my case it's not practical: we have >three 800-watt amps driving the main PA and another 800-watt amp driving >the monitors, in addition to two guitar amps, a bass amp, a keyboard amp >and the rest of my keyboard setup all on stage. [...] > >So, if a tree layout isn't viable, what's a poor e-musician to do? Find somebody that really (really) knows some basic electrical wiring (if you have a friend in NECA it would help ). I would not advise doing this as a bathtub experiment. The basic idea is to build your OWN service box. A short rack on casters is great and will hold the box, cables, and outlets. It should house a fair-size distribution box with independent breakers. Have your ETech friend rig the outlets. Now, the trick part, wire the supply-side of the distribution box to a 240-v circuit breaker plug and plenty of outdoor-rated feed cable. When you arrive at a gig, go to their distribution panel, pop out an existing breaker, and pop in your plug. Whammo... an entire service, common ground, overload protected, that can handle up to the supplying panel's main breaker current rating. This is pretty common practice in mid-size road shows. The larger shows request taps directly to mains. Some shows here at our arena have requested up to 300kVa mains for lighting (that'll seriously cook your goose) and smaller, separate mains for PA (reduces dimmer pack "buzz" too). /Jeff/ ------------------------------------------------------------- Date: Mon, 14 Jan 91 16:17:00 EST Reply-To: miller@SOL.CS.ROCHESTER.EDU Sender: Electronic Music Discussion List From: Brad Miller Subject: Re: Grounding question In-Reply-To: <9101141423.AA28156@cayuga.cs.rochester.edu> Just a couple very minor points on all the mostly very accurate stuff that has already been posted: If your house has polarized plugs, the larger one is supposed to be neutral (in case you need to futz with it). Terminology: HOT carries the current from the service box to the appliance. One HOT for 120, two HOT for 220. Normally this wire is white (in 120). Local code may differ on color scheme. NEUTRAL carries the current from the appliance back to the service box. One needed for either 120 or 220. Normally this wire is black (in 120). Local code may vary on color scheme. GROUND used for safety purposes. Required (by code) for 120v lines only, but may be present as a fourth wire in 220. This wire is required to be green universally to my knowledge. The third pin (green wire GROUND) and neutral are connected together in the service box (at least according to local code), but that does NOT mean they are the "same" at the application end (where you plug something in). In particular, the GREEN GROUND is inteded to be a safety feature for the user only. That is, a metal case connected to green ground will prevent a internal HOT wire shorting to the case electrocuting the user, as has been mentioned. If a device shorts internally NEUTRAL to GROUND they are in violation of code, and create a ground loop. The only place these are to be connected are at the service box (i.e. where your circuit breakers and/or fuses are) and nowhere else. One does not normally want to use GROUND as NEUTRAL because 1) the safety feature of having separate paths is gone, and 2) a small amount of voltage might appear on the surface of appliances that are on this branch. If the user were to touch both this appliance and another on a different branch... 3) you can get a ground loop as mentioned... 4) you will trip any GFIs on the circuit, regardless of the presence of an actual fault. All cold-water metal pipes in the building must be connected to EARTH GROUND. This is normally taken from the cold water service into the building (since it's copper and well grounded), a wire is used to connect the EARTH GROUND from one side of the water meter to the other. Electrical GROUND should be connected to EARTH GROUND at one point, only, but EARTH GROUND provided by metal pipes may be used as an alternative to GROUND for user service in the building (but not for neutral). Technically this should only be needed for old construction, since newer construction all require a separate green wire GROUND be provided at each service outlet, so I don't know why one would need the EARTH GROUND provided by the pipes for service reasons. I'm not an electrician, but I had to study up on the code to rewire my basement :-). ---- Brad Miller U. Rochester Comp Sci Dept. miller@cs.rochester.edu {...allegra!rochester!miller} ------------------------------------------------------------- Date: Mon, 14 Jan 91 16:30:00 EST Reply-To: miller@SOL.CS.ROCHESTER.EDU Sender: Electronic Music Discussion List Comments: corrections added From: Brad Miller Subject: Re: Grounding question (CORRECTED VERSION) In-Reply-To: <9101141423.AA28156@cayuga.cs.rochester.edu> Just a couple very minor points on all the mostly very accurate stuff that has already been posted: If your house has polarized plugs, the larger one is supposed to be neutral (in case you need to futz with it). Terminology: HOT carries the current from the service box to the appliance. One HOT for 120, two HOT for 220. Normally this wire is WHITE (in 120). Local code may differ on color scheme. < PREVIOUS MESSAGE SAID WHITE. OOPS. IN FACT IF YOU USE WHITE, YOU ARE SUPPOSED TO WRAP EACH END IN BLACK ELECTRICAL TAPE TO SIGNAL THIS. > 220 SEEMS TO DIFFER MORE THAN 120. SOME USE BLACK/ RED GREEN - THERE IS NO NEUTRAL BECAUSE THE 2 LEGS ARE USED TOGETHER. WHITE NEUTRAL MUST ONLY BE PROVIDED IF THE TWO LEGS WILL BE USED SEPARATELY WITH RESPECT TO NETURAL (for instance stoves with convenience outlets of 120). NEUTRAL carries the current from the appliance back to the service box. One needed for either 120 or 220. Normally this wire is WHITE (in 120). Local code may vary on color scheme. GROUND used for safety purposes. Required (by code) for 120v lines only, but may be present as a fourth wire in 220. This wire is required to be green universally to my knowledge. IT MAY ALSO BE BARE. The third pin (green wire GROUND) and neutral are connected together in the service box (at least according to local code), but that does NOT mean they are the "same" at the application end (where you plug something in). In particular, the GREEN GROUND is inteded to be a safety feature for the user only. That is, a metal case connected to green ground will prevent a internal HOT wire shorting to the case electrocuting the user, as has been mentioned. If a device shorts internally NEUTRAL to GROUND they are in violation of code, and create a ground loop. The only place these are to be connected are at the service box (i.e. where your circuit breakers and/or fuses are) and nowhere else. One does not normally want to use GROUND as NEUTRAL because 1) the safety feature of having separate paths is gone, and 2) a small amount of voltage might appear on the surface of appliances that are on this branch. If the user were to touch both this appliance and another on a different branch... 3) you can get a ground loop as mentioned... 4) you will trip any GFIs on the circuit, regardless of the presence of an actual fault. All cold-water metal pipes in the building must be connected to EARTH GROUND. This is normally taken from the cold water service into the building (since it's copper and well grounded), a wire is used to connect the EARTH GROUND from one side of the water meter to the other. Electrical GROUND should be connected to EARTH GROUND at one point, only, but EARTH GROUND provided by metal pipes may be used as an alternative to GROUND for user service in the building (but not for neutral). Technically this should only be needed for old construction, since newer construction all require a separate green wire GROUND be provided at each service outlet, so I don't know why one would need the EARTH GROUND provided by the pipes for service reasons. I'm not an electrician, but I had to study up on the code to rewire my basement :-). SORRY FOR THE PRIOR ERRORS ---- Brad Miller U. Rochester Comp Sci Dept. miller@cs.rochester.edu {...allegra!rochester!miller} ------------------------------------------------------------- Date: Mon, 14 Jan 91 16:51:00 EST Reply-To: miller@SOL.CS.ROCHESTER.EDU Sender: Electronic Music Discussion List From: Brad Miller Subject: Oh foo. Rereading my "corrected" copy, I realize it still may be confusing. So in one sentence, 120 service, HOT is black. Short blade of outlet. NEUTRAL is white. Taller blade of outlet. GROUND is green or bare. Round or upside-down U blade of outlet. Whew. Next time I write the message and wait a day before posting :-). ---- Brad Miller U. Rochester Comp Sci Dept. miller@cs.rochester.edu {...allegra!rochester!miller} ------------------------------------------------------------- Date: Tue, 15 Jan 91 19:27:46 GMT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: "Benjamin M. J. Ellis :->" Subject: Re: Earth loops Yo! All this earthy stuff is very interresting, and brings back so many good (sic) memories for me 8-) There is, however, one solution no one has mentioned which also works REALLY well, and is REALLY safe!!! I discovered it when I noticed my record deck was humming... this was due, of course, to an earth loop. The problem was, there shielding of the audio cable connecting it to the pre-amp was earthed, not only that, but also the record deck motor was earthed as well but none the less, separately... problem... nice big unwanted loop, since the motor was connected to the chassis, and the chassic to the audio connector ground... etc... etc... any the at the time I wanted to fix it quickly (I had a new record to [ list to okay?!??!)... the solution was to run and EXTRA ground, later I found this invaluable in PA work... you set up, get a humm... don't know the bands equipement, have 1 hour to sound check, no time to faff around, so just run a few extra earth wires to get rid of all those unwanted potention differences (voltages)... well it works, its hap hassard, but ALOT less dangerous than "lifting the earth" eeekkk... -Benjamin U.K.C. England --------------------------------------------------------------- P.S. in the next two weeks or so I'm test the bass synth so thanks to everyone for the pick up advice, lets pray it works!!!! ------------------------------------------------------------- Date: Wed, 16 Jan 91 11:36:20 GMT Reply-To: Electronic Music Discussion List Sender: Electronic Music Discussion List From: Nick Rothwell Subject: Re: Oh foo. >HOT is black. Short blade of outlet. >NEUTRAL is white. Taller blade of outlet. >GROUND is green or bare. Round or upside-down U blade of outlet. .which confused the hell out of me last weekend when I was rewiring some American mains cables (black == live indeed...). The old British system used to be: LIVE: red NEUTRAL: black EARTH: green. Now we've adopted the European system, which is LIVE: brown NEUTRAL: blue EARTH: green/yellow stripe. Just in case this is of use sometime... Nick. -------------------------- End of the EMUSIC-L Digest **************************