Members ShiftChange564 Posted February 11, 2009 Members Share Posted February 11, 2009 Looking for a good cheap testing tool I can use to check voltages, grounds, etc... I keep running into ground loops when I use more than one 120 volt outlet for my larger multi-rack rig. I don't think I'm ready to jump on the 240 volt single phase bandwagon yet. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 11, 2009 Members Share Posted February 11, 2009 A circuit tester is not going to give you the information you need to diagnose a ground loop problem. Ground loops are generally an issue because the design of the interconnect wiring has not been well engineered to minimize exposure to the effects that ground loops cause. This can be as simple a sbeing thorough about using all balanced interconnects, using 1:1 isolation transformers on equipment that needs isolation, insuring the pin 1 on XLRs is not tied to the shell, etc. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 11, 2009 CMS Author Share Posted February 11, 2009 It's still a good idea to have a simple $7 outlet tester to see if the thing's working, grounded, and not phase-reversed. See your local hardware store, or one of the big box stores for this. But definitely consider what Andy wrote...it'll take you a long way toward a quiet rig in most venues. You can't control the venue wiring, but you can control yours. Link to comment Share on other sites More sharing options...
Members Coaster Posted February 12, 2009 Members Share Posted February 12, 2009 .... and not phase-reversed.. i'm suprised how often i find this. what is the correct protocol for dealing with this in places where it is inappropriate to 'make it right'? Link to comment Share on other sites More sharing options...
Members burdizzos Posted February 12, 2009 Members Share Posted February 12, 2009 I usually mention it to the club owner and find a properly wired receptacle for my 50 foot 12/3 extension cord. If I'm ahead of schedule, I offer to fix it, but I've never been taken up of the offer. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 12, 2009 CMS Author Share Posted February 12, 2009 I've found the proper protocol is to tape off the dysfunction outlets and notate on the tape the dystfunction. Only use the outlets that test-out properly. Bringing the problem (s) to the venue management will only result in a come-back look like a cow looking at a new gate... so there's no point in that. Guarenteed your tape will still be there over the same outlets 5, 10, 20, or even 30 years later... as I can testify to. Yep, yep, yep (with a ...I love that cow/gate line!) and.....yep. Many of us here can safely and completely repair/rewire bum outlets, but we're not in that business, and to do so in a commercial venue requires that you be in that business, with all licensing, permits, liability insurance, and permissions that go with it. Hence why the management will give you 'that look' if you bring it up. Mostly, you're talking, and they're seeing $$$$$$$$$$ where your face should be. Link to comment Share on other sites More sharing options...
Members burdizzos Posted February 12, 2009 Members Share Posted February 12, 2009 Yep, yep, yep (with a ...I love that cow/gate line!) and.....yep. Many of us here can safely and completely repair/rewire bum outlets, but we're not in that business, and to do so in a commercial venue requires that you be in that business, with all licensing, permits, liability insurance, and permissions that go with it. Hence why the management will give you 'that look' if you bring it up. Mostly, you're talking, and they're seeing $$$$$$$$$$ where your face should be. I started carrying around the business cards of a Master Electrician that works for me. He's got his own private company and hustles on the side for extra income. I'm sure he'd love nothing more than to come out and rewire a few receptacles... For no less than $150. At the places where swapped neutrals and hots are most common, a licensed electrician won't touch {censored} unless they pay him to fix all of the serious problems due to liability. I know that I wouldn't touch anything as a licensed electrician in a bar that used 16/3 orange extension cords as power drops on their "stage" unless they paid me to bring the whole thing up to code. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 12, 2009 Members Share Posted February 12, 2009 A swapped neutral/hot will not cause the kind of noises that the OP describes. In fact it will function normally, except that it violates safety protocol. Specifically on Edison base lamps the shell will be hot. It should still be corrected absolutely. All pro audio gear is transformer isolated on the AC line side. Link to comment Share on other sites More sharing options...
Members burdizzos Posted February 12, 2009 Members Share Posted February 12, 2009 A swapped neutral/hot will not cause the kind of noises that the OP describes. In fact it will function normally, except that it violates safety protocol. Specifically on Edison base lamps the shell will be hot.It should still be corrected absolutely.All pro audio gear is transformer isolated on the AC line side. That isn't limited to lights. Some rack gear will have a hot chassis with a swapped hot/neutral. I found that out the hard way, which is why I promptly invested in a receptacle tester for the gig bag. It's rare that I will see that, the most common problem is a missing ground. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 12, 2009 CMS Author Share Posted February 12, 2009 I started carrying around the business cards of a Master Electrician that works for me. He's got his own private company and hustles on the side for extra income. I'm sure he'd love nothing more than to come out and rewire a few receptacles... For no less than $150.At the places where swapped neutrals and hots are most common, a licensed electrician won't touch {censored} unless they pay him to fix all of the serious problems due to liability. I know that I wouldn't touch anything as a licensed electrician in a bar that used 16/3 orange extension cords as power drops on their "stage" unless they paid me to bring the whole thing up to code. Which then begs the question; how'd the place get its C.O. in the first place? When's the last time it was (or was it ever) inspected? Oh well, I suppose if you can ship salmonella-tainted peanut products all over the US, you can run a bar with some dangerous electric....until someone dies. And that's the bottom line. Little ever changes until someone dies. You don't see a traffic light at an intersection until you've driven past a few fatals at that spot. Sad. Link to comment Share on other sites More sharing options...
Members burdizzos Posted February 12, 2009 Members Share Posted February 12, 2009 Which then begs the question; how'd the place get its C.O. in the first place? When's the last time it was (or was it ever) inspected?Oh well, I suppose if you can ship salmonella-tainted peanut products all over the US, you can run a bar with some dangerous electric....until someone dies. And that's the bottom line. Little ever changes until someone dies. You don't see a traffic light at an intersection until you've driven past a few fatals at that spot. Sad. Given the very unlikely possibility that someone will die as a result of an improperly wired receptacle, I'm confortable with the current level of local gov't bureaucracy. The fact is that I can make a call and get a fire marshall/electrical inspector into a place if I feel they have a serious safety issue or if the club owner is a total dick when I tell him that he has improper wiring. Public safety policy must serve both the taxpayers and the people who pay the taxes. A city would bankrupt itself trying to make the place safe for idiots unless there was some kind of risk management factored in. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 12, 2009 CMS Author Share Posted February 12, 2009 Given the very unlikely possibility that someone will die as a result of an improperly wired receptacle, I'm confortable with the current level of local gov't bureaucracy. The fact is that I can make a call and get a fire marshall/electrical inspector into a place if I feel they have a serious safety issue or if the club owner is a total dick when I tell him that he has improper wiring. Public safety policy must serve both the taxpayers and the people who pay the taxes. A city would bankrupt itself trying to make the place safe for idiots unless there was some kind of risk management factored in. I was speaking more to the more serious electrical atrocities I've witnessed than specifically only a reversed receptacle. The stuff like extension cords run as permanent feeds (even seen 'em *in* walls!) to the stage as you mentioned. But even a reversed recep makes me wonder if the place was ever inspected prior to occupancy. And it makes me wonder about the rest of the wiring...reversing phase is a cardinal sin of electricians. It doesn't take more than 5 min to test all of the outlets in any gin mill. They don't reverse on their own after that..... Link to comment Share on other sites More sharing options...
Members burdizzos Posted February 12, 2009 Members Share Posted February 12, 2009 Swapping a hot and a neutral probably happens when a receptacle gets broken and the bar owner gets the bar back to fix it. The ground is easy to figure out, but the other two aren't as obvious. If an idiot is given a 50/50 chance, 90% of the time, he will get it wrong. Extension cords as permanent feeds don't really bother me that much. It just looks crappy and doesn't inspire confidence in the wiring that it is plugged into. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 12, 2009 CMS Author Share Posted February 12, 2009 Swapping a hot and a neutral probably happens when a receptacle gets broken and the bar owner gets the bar back to fix it. The ground is easy to figure out, but the other two aren't as obvious. If an idiot is given a 50/50 chance, 90% of the time, he will get it wrong. Extension cords as permanent feeds don't really bother me that much. It just looks crappy and doesn't inspire confidence in the wiring that it is plugged into. I tend to look at things like this as little nuggets of info...clues as to how my day, night and future will likely go. If the place is tight, clean, and looks like it'll be there tomorrow, there's a 0.01% better chance the owner isn't going to stiff me or be a raging hardon. If the wiring looks like it was installed by my brother in-law using kitchen implements, and the place generally looks as if it was used as a foreign set for The Unit, my day could get 'interesting'. I've seen brand new wiring with all manner of problems. As an example I ran a shop that had a renovation/expansion. The contractor hired some fly-by-nights, and one of my guys was nearly electrocuted because of a wiring fault. I went over the rest of it personally, and found a dozen problems, 3 of them possible killers. Got the inspector in (AGAIN) and had the work flagged, which was a contractual requirement to get the contractor to fix it (nice huh?) right. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 13, 2009 Members Share Posted February 13, 2009 That isn't limited to lights. Some rack gear will have a hot chassis with a swapped hot/neutral. I found that out the hard way, which is why I promptly invested in a receptacle tester for the gig bag.It's rare that I will see that, the most common problem is a missing ground. I can't think of a single piece of rack gear that has a hot chassis. If it did, the ground pin bonding would automatically trip the breaker. In fact, all rack gear that I know of is transformer isolated from the AC mains and there is absoluetly no direct neutral or hot connection to the chassis. There would be no way of getting any safety approvals for a direct connection. Link to comment Share on other sites More sharing options...
Members Coaster Posted February 13, 2009 Members Share Posted February 13, 2009 the designers of these outlets gave us a clue; in this case the clue is simply "black gold" Link to comment Share on other sites More sharing options...
Members Coaster Posted February 13, 2009 Members Share Posted February 13, 2009 maybe we should engrave on these shmucks foreheads then; reversed of course so they can read it in the mirror? Link to comment Share on other sites More sharing options...
Members Dark Ice Posted February 13, 2009 Members Share Posted February 13, 2009 Correct, because most hacks would automatically assume black is neg and white is pos. I liked the old british convention. Red is live and Black is neutral. Nobody could guess that wrong Steve. Link to comment Share on other sites More sharing options...
Members Keyrick Posted February 13, 2009 Members Share Posted February 13, 2009 Ground loops are generally an issue because the design of the interconnect wiring has not been well engineered to minimize exposure to the effects that ground loops cause. Absolutely. Most commercial electricians, and many electrical engineers who work in commercial construction, don't think about grounding issues other than standard code requirements, which are based on equipment protection and life saftey. I have worked on projects where the electrical contractor was to have installed an isolated ground system and they rarely get it correct. "After all, a ground is a ground, whether you home run it per design, or you splice it at the first convienent location!" is a paraphrased sentence I have heard more than once. And in most club locations, power for the band is an afterthought. There are folks out there who know how to do it correctly. Some places are just fine. Even in a properly wired system by code, you can get noise by a difference in induced potential on grounds from recepticles that are on different circuits. The only way to really test for it is to do a current analysis of the Main Switch gear and distribution panels. Most sound guys aren't gonna do that! So the best advice I can provide is to echo a recomendation in an earlier post which stated that you get a bunch of isolation transformers from Andy. I did and they work just fine! Rick Link to comment Share on other sites More sharing options...
Members JohnnyGraphic Posted February 13, 2009 Members Share Posted February 13, 2009 O.K. Not to sound like an idiot, but when you say isolation transformer, are you talking about DI's? And, to minimize the ground loops, use XLR connections wherever possible right? 1/4" TRS may or may not work. Right? Thanks for being patient! Johnny Link to comment Share on other sites More sharing options...
Members burdizzos Posted February 13, 2009 Members Share Posted February 13, 2009 I can't think of a single piece of rack gear that has a hot chassis. If it did, the ground pin bonding would automatically trip the breaker. In fact, all rack gear that I know of is transformer isolated from the AC mains and there is absoluetly no direct neutral or hot connection to the chassis. There would be no way of getting any safety approvals for a direct connection. I don't know what to tell you. I had 110 on my rack case at one point because of a swapped hot and a neutral. Something in there had the neutral tied to ground. I'll never know because I no longer have any of that gear. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 13, 2009 CMS Author Share Posted February 13, 2009 And, to minimize the ground loops, use XLR connections wherever possible right? 1/4" TRS may or may not work. Right? Thanks for being patient!Johnny Electrically there's no difference between an XLR and a TRS...both have 3 contact points so a balanced signal CAN be carried through either. Whether the signal is balanced or not when you're using a TRS depends on the gear. Be sure it's balanced, and not for example, stereo, or a TS connection. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 13, 2009 CMS Author Share Posted February 13, 2009 I don't know what to tell you. I had 110 on my rack case at one point because of a swapped hot and a neutral. Something in there had the neutral tied to ground. I'll never know because I no longer have any of that gear. Was it a vintage tube amplifier? I've seen them wired with no ground and the neutral tied to the chassis and of course a non-polarized 2-prong plug. May as well call it a widow-maker. Link to comment Share on other sites More sharing options...
Members burdizzos Posted February 13, 2009 Members Share Posted February 13, 2009 Was it a vintage tube amplifier? I've seen them wired with no ground and the neutral tied to the chassis and of course a non-polarized 2-prong plug. May as well call it a widow-maker. Ewww, tubes? The only tube amp I own is a '68 Bassman that I've been meaning to repair for the last ten years. It won't fit in a rack case. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 13, 2009 Members Share Posted February 13, 2009 Sorry for the confusion, the isolation transformer I was referring to in this case was the AC power transformer which is UL (or agency) listed as an isolating device in that everything on the secondary side is isolated from the primary AC wiring. It's a defacto safety requirement in all developed countries. There will be no (practical) current flow between a chassis and any secondary conductor... in fact the leakage current is governed by agency rules. Burdizzos, think about this for a minute... if the chassis is solidly grounded there can be no voltage on the chassis regardless of what connector is connected to the chassis. If the hot was connected it would open the overcurrrent protection device. If the neutral was connected to the chassis you would have a current proportional to the difference in voltage between the neutral and ground divided by the impedance to ground. Generally this is in the 10's of mA. I'm saying the situation you describe is impossible unless the chassis bond is defective, the ground wiring is defective, the neutral-ground bond atthe service panel is defective or it's an ungrounded chassis with a defective power transformer. Isolated grounding schemes are commonly messed up. The concept is simple as hell, but the guys in the field often just don't get it. One of the big reasons for the isolated ground wiring is that conduit bonds are often noise and intermittent on a mVolt level and they touch building steel at various locations in an installation that may be hunderds of feet apart, so there can be small induced currents that generate ground potentials across different receptacles. I always inspect the IG installations that I design during the rough-in and finish stages, and discuss with the lead electrician that I will be inspecting so it's to their advantage to ask questions because the other option ifthey get it wrong is to start over at their cost. Link to comment Share on other sites More sharing options...
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