mmiles Posted November 6, 2003 Share Posted November 6, 2003 Please reply if you can help me in this situation... In my business (PC-Based POS systems) this is a critical area in our "site-prep" specs. DEDICATED in our mind is an outlet that services our equipment only on it's own breaker. ISOLATED ground is such that each outlet on that circuit has a "home-run" ground wire back to the panel. The electrician, like most, got the dedicated part just fine but he, and most for that matter, struggle with the isolated ground. This is what he did. The first outlet has the home run for all conductors back to the panel. From that outlet to the remaining outlets in that run on that circuit are "daisy-chained" (all wire is 12/2). At each junction the grounds are "bonded" (4-5" tightly twisted with a 1-2" tail for the screw lug NOT just wire nut connections). This makes for one "mechanical" ground for that circuit. This is not an isolated ground in my mind. When dealing with digital electronics of any kind grounding is crucial to performance. With the solution supplied by the electrician there is "potential" for inductance, impedance and capacitance issues when the circuit is under load especially from the amp and sub woofer therefore the pre/pro (A/V computer if you will) to error or injected hum into the signal. So is the electricians method acceptable or should I insist on home run grounds? Urgent replies requested please. Regards, Mike Quote Link to comment Share on other sites More sharing options...
FirebirdTN Posted November 6, 2003 Share Posted November 6, 2003 I am no expert, but I think you are asking a little too much. Your desired "grounding" scheme may well be against the NEC code. (Maybe, maybe not, I do not know). Working in broadcast, connecting quite a large amount of digital and analog equipment, I am somewhat familiar (but not an expert) on grounding. The biggest thing I see when people refer to "grounding" is alot of folks seem to think there is only one type of "grounding", which actually is not true. There are at least 4 different and distinct purposes of grounding. They are: 1) To reference a signal. Example, the peak voltage of signal A is +5 volts, with respect to point "C" in a circuit. Or the peak voltage of signal B is +12 volts in a circuit, again, with respect to point "C". Point "C" in this case would be a reference point, or "ground", even though it may not necessarilly be at 0 volt potential with respect to "earth ground". 2) Safety ground. This applies to all equipment that has a 3-wire power cord. The "ground" lug is "earthed" thru the electical wiring to prevent a shock hazard. Ever been to an arcade that when you touched two different video game cabinets at the same time you felt a jolt? I have, and that is a faulty ground. Or maybe if you touch your washing machine and dryer at the same time you get a jolt? This situation is VERY hazardous, and under no circumstances should you EVER defeat a saftey ground. Although doing so doesn't itself usually present a shock hazard, if there is a malfunction in the equipment, a properly earth grounded applicance will either trip the breaker, or at very least keep the cabinet from becoming a shock hazard. If you defeat the safety ground, you no longer have this protection. 3) RF Shielding. In environments that have high RF fields (such as factories, or communications centers like radio, TV, etc), Often times the RF energy is so strong, it can induce current flow in wiring or electronics themselfs, and often times this energy will be demodulated by a semiconductor device operating non-linearly, and produce audible interferance. Ever heard a radio station in your telephone? 4) Surge/Lighting protection. With outdoor antennas and such, the object here is, any radiator high up in the air becomes and effective lightning rod. If the antenna structure is "earthed", the hope is, if it takes a direct lighting strike, the current will flow from the earth up thru the antenna structure, rather than from the earth, thru your equipment, and then up thru the antenna structure. There is alot more to it that just for aerials, but this is basics. Problem is, often times, these different grounding purposes become at odds with one another. What maybe good for one purpose, maynot necessarily be good for another. In your particular case, what is it exactly you are trying to accomplish? -Alan -EDIT- In your particular case, I assume you are trying to prevent a ground loop hum? I am unsure of how or even if a ground loop could afftect a digital signal (its all states of high or low voltages), but if you have any points of analog, then you could have the potential for ground loops. Is this what you are trying to prevent? Quote Link to comment Share on other sites More sharing options...
Malcolm Posted November 6, 2003 Share Posted November 6, 2003 An isolated ground receptacle is indeed permitted by NEC Section 250-146(d). Its purpose is to minimized problems caused by noise or transients on the ground. The outlet has an orange triangle on its face. The equipment ground screw on the outlet is not connected to the yoke as on standard receptacles. If one is installed in a metallic box, it must have a nonmetallic faceplate to eliminate the possibility of shock. The ground wire is run all the way back, through any subpanels on the way without grounding, to the main panel where it is grounded at the point where the system neutral is bonded to the grounding electrode (the equipment grounding bus in the main panel). If your installation does not look like this, you electrician did not do the job correctly. Quote Link to comment Share on other sites More sharing options...
Bruinsrme Posted November 6, 2003 Share Posted November 6, 2003 Mike, First I thought you had the Parasound A51, profile says a52. POS point of sale, or is it a spec computer for design? Are you looking for a isolated ground for the computer? Personally I think you need to be very concerned about the incoming voltage supply. all to many times vital computers are place on sub boxes and are not receiving enough voltage, or the powersupply of the computer is less than adequate. Voltage to a computer is more of my concern especially with my DNS and storage servers. The best way to kill a computer is to have too small of a power supply. For vital computers a UPS nd or a method of monitoring incoming voltage is imperative more so than the isolated ground, IMHO. Flourescent lights create enough transients to kill the benefits of a dedicated ground, again MHO. Voltage coming out of a recepticle is garbage, and it needs to be cleaned up for critical applications. I can understand your concerns but after seeing all sorts of various voltages running parallel to each other on the submarine sometimes I wonder if we worry about things because..... Quote Link to comment Share on other sites More sharing options...
Guest BobG Posted November 7, 2003 Share Posted November 7, 2003 Generally speaking, for audio purposes, isolated grounds are not a good idea as they encourage ground loop noise. Common ground among all ac receptacles will minimize potential ground loop noise. Quote Link to comment Share on other sites More sharing options...
Rudy81 Posted November 7, 2003 Share Posted November 7, 2003 Mike: I agree with BobG. I think it will be just fine as is. I have a dedicated 20Amp circuit to my media room, nothing I had done, it just turned out that way when I purchased the house. I'm sure it does not have any special grounding. I have not had any ground loop problems and ever since going to the unbalanced HALO outputs, I have absolutely no noise in the system. Is there any way you can temporarily set up part of your system and take a listern? Quote Link to comment Share on other sites More sharing options...
mmiles Posted November 8, 2003 Author Share Posted November 8, 2003 Malcolm is correct. The electrician got the spec from the local inspector. I to had the spec from on of the equipment manufactures I represent. Indeed there are multi "ground" issues as the broadcast gentleman (sorry I goofed and forgot your screen name) mentioned. Logic and saftey ground are the most crucial. Logic has to be clean as possible, less the .5 volts neutral to ground. Bruins I sell PC Based Point of Sale systems. I do have the big boy HALO my signature is outdated. I agree somewhat with your statements but remember the gear we use today with regulating power supplies should correct from 85 - 140v back to 120. I still say "power conditioning" (low/no common mode noise) is more vital the stabalization (constant 120v). This will also depend on your area to of course. BobG. The first way I metioned (home running and extra ground) would not have passed code. It did provide a "safety ground" but not a clean "isolated" logical ground reference of the desired 0 volts. The goal was to reduce noise and provide a good consistant logical ground and get rid any ground loop potentional. Rudy glad to hear your hum is gone dude! It kinda of a pain in the a55 to hook stuff up. Hey I guess I should test it at some point. It's been tucked away for almost 3 months now with about 4 to go! Regards, MIke Quote Link to comment Share on other sites More sharing options...
marksdad Posted November 9, 2003 Share Posted November 9, 2003 grounding is a touchy subject, not because of grounding itself, but because every engineer thinks it should be done in priority, the nec touches on the most basic concepts, actually everyone is correct, except the remark about 4 types of grounding, there are many types of grounding, as there are many applications for grounding. but for a true isolated ground, a person must set up seperate ground rods, ufers.... and than use a totally seperate ground buss, it cannot contact the remaining system in any way. i have seen seperate buss installed in pannels, isolated from the other ground, but still having a conductor terminating at the main ground buss, this is dedicated, not isolated, and when it comes right down to it a system still picks up on all system noise through the buss, isolating a ground is very difficult and expensive Quote Link to comment Share on other sites More sharing options...
FirebirdTN Posted November 9, 2003 Share Posted November 9, 2003 Ummmm....I was the one who stated there was at LEAST 4 differet purposes for grounding. And, I am possitive that my statement is accurate. There maybe even more, but the ones I listed are the ones I deal with on a daily basis in broadcast engineering. Take another look. -Alan Quote Link to comment Share on other sites More sharing options...
fini Posted November 9, 2003 Share Posted November 9, 2003 Fascinating stuff! For a truly isolated ground, you must run your ground wire to a different planet (the Moon would work here, too). I'd use a little bigger gauge than #12, though. Also, you're gonna want to sink that ground rod pretty deep, so it doesn't pull out. fini Quote Link to comment Share on other sites More sharing options...
marksdad Posted November 10, 2003 Share Posted November 10, 2003 its cheating but i have seen many cases where the rod is lain flat, this is more in line with a ufer ground Quote Link to comment Share on other sites More sharing options...
Q-Man Posted November 10, 2003 Share Posted November 10, 2003 I put in a dedicated 30 amp circuit about two years ago. I have it hooked up to my commond ground in the panel box. Quote Link to comment Share on other sites More sharing options...
mmiles Posted November 11, 2003 Author Share Posted November 11, 2003 It is against code in my state (Maryland) to have more than one "earth" ground when using one service (meter) at the home not matter how many panel boxes you have. Needless to say he (electrician) pulled it all out and re-wired. Like we say around here... "there's always enough time to do it over but never enough time to do it right in the beginning". In other words if you go the extra step and put in the extra effort at first, even though it will take longer, you will save time and aggrevation in the end. Regards, Mike Quote Link to comment Share on other sites More sharing options...
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