I have asked them for specifics and they came back with 8 dedicated quad outlets in conduit with iso ground fed off a dedicated 200 amp panel board (panel for outlets only) 200 amp to be located near studio, the home is in framing stage with a 400 amp main panel. I guess I will folow the wise advise of mdshunk Give em what they want.
recording studio
- Thread starter normbac
- Start date
- Status
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Bob, I'm not claiming to be a proponent of all of the recommended procedures I've read about, and I agree that, with the power-transformer isolation, the audio circuits should not care how the primary conductors are supplied.iwire said:Larry how does that have anything to do with placing all the circuits on one phase?
However, my understanding is that it is better if (1) the inevitable grounded-conductor voltage drops are all in the same direction, and (2) the hots are of the same voltage, and not 240 volts apart. There is no such thing as 100% isolation.
normbac said:
Sorry but I cannot help but laugh. Let me ask a very stupid question here.
Is this a wood framed house?
If so and you run NM to plastic boxes with standard outlets you have IG. Otherwise I agree with Mark, give them what they want, take the money, and run laughing all the way to the bank before they figure it out..
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iso ?
iso ?
Isolated Grounding: A Waste of Good Copper?
By Doug Criner
A Chicago-area public high school was recently rewired to add 120-V receptacles for personal computers. The designer specified isolated grounding?with those orange-colored receptacles that seem so reassuring.
Each receptacle was served by four conductors: an AWG No. 12 black (hot), a No. 10 white (neutral, or "grounded conductor"), a No. 12 green (redundant raceway ground), and a No. 12 striped green (isolated equipment ground)?all installed within a grounded, steel conduit. Let?s consider what on Earth might be going on here.
Four Conductors
The black hot wire is about the only thing that makes absolute sense. The oversized neutral is evidently based on the possibility that harmonics, generated by nonlinear loads, such as computers, can overload the neutral conductor of a 3-phase, 4-wire, wye-connected circuit. However, for a single-phase circuit, even a 120/240-V circuit with a shared neutral, it is virtually impossible for the neutral current to exceed the phase current. Therefore, there is no reason for over-sizing the neutral.
The raceway ground conductor is not a bad idea, since it provides redundancy to the ground path provided by the steel conduit. Such a redundant ground conductor, while not required by the National Electrical Code, is often specified for peace of mind in case the conduit develops loose or corroded connections. (In an isolated-ground system, a redundant raceway ground conductor is bonded to the receptacle box, but it is not connected to the ground terminal on the receptacle.)
The isolated ground conductor is connected to the ground connector on the receptacle and can then be run back to the service ground bus, unconnected to the ground bus of intermediate panels. What is the purpose of such an isolated ground system? Interestingly, you may get several different answers, depending upon whom you ask.
Purpose of Iso-Ground?
One explanation is that some manufacturers of sensitive electronic equipment "require" that their equipment be supplied by an isolated ground system. This explanation is a little weak?first, because such a system is certainly not required by manufacturers of personal computers and, second, because equipment manufacturers are not necessarily the sole authority on power distribution.
(An example comes to mind: some equipment manufacturers once "required" that their equipment be grounded to a separate building ground rod, isolated from the building?s regular electrical ground?an unsafe practice that is prohibited by the NEC. In my opinion, equipment manufacturers should themselves be "required" to design their equipment to be compatible with any power distribution system design that meets the NEC.)
Another explanation is that an isolated ground system affords greater personnel safety against shock?which is why the orange receptacles are seen in hospital rooms, right? However, the NEC does not require an isolated ground system in hospital rooms. (The NEC does require a redundant ground conductor in the hospital?s raceway but not an isolated ground. Interestingly, the NEC allows an ungrounded system in hospitals, which is the Gold Standard of shock protection, at least for the first ground fault.)
Another theory is that in the event of a ground fault, the fault current passing through the electrical raceway can raise the voltage of the raceway, and any connected equipment grounds, enough above ground potential to be a shock hazard. Studies at the Georgia Institute of Technology do not support this concern.
Some people think that an isolated ground system somehow alleviates power quality problems caused by nonlinear power supplies. Yes, computers do introduce harmonics because their power supplies chop up the sinusoidal current. Perhaps these harmonics might, in turn, cause problems to other electronic equipment. But these harmonics are propagated through the hot and neutral conductors, and no jiggering of the branch grounding conductors will prevent this.
Another justification cited for isolated grounds has to do with the effects of ground loops, those pesky things that can play havoc with low-voltage data signals. But we?re dealing here with 120-V power, not low-voltage data, and if things are installed properly, there should be no current in the grounding path, except during a ground fault?when ground loops will be the least of our worries.
Noise Suppression
The final argument, and the only one sanctioned by the NEC, is that an isolated ground system may reduce electromagnetic noise interference from appearing on the branch circuit. (In fact, the NEC permits the use of an isolated ground system only where required to reduce electromagnetic noise interference; thus, anybody who insists there is any other reason for installing isolated grounding is caught in a Catch 22?and prohibited by the code from installing an isolated ground.)
Large currents in nearby circuits can induce small, unwanted 60-Hz voltages in the grounded raceway of another circuit and the grounded cases of any plug-and-cord equipment. Possibly, some poorly isolated equipment might be sensitive to this?certainly, old-fashioned AC-DC tube-type radios, whose filaments were connected across the AC line, were prone to an annoying 60-Hz hum.
But for most situations, this theoretical concern should be negligible, unless you happen to be located next to an arc welder. To the extent that a separate, isolated ground conductor will be shielded by its steel raceway, it logically follows that current-carrying conductors in another, adjacent circuit would also be shielded. Further, induced voltages between separate circuits are unlikely to occur when the conductors of each circuit are tightly bundled, which will cause induced voltages to be self canceling. In any case, if a redundant ground conductor is pulled inside the steel conduit, and bonded to the receptacle and box, it seems likely that any 60-Hz hum would be suppressed.
At What Cost?
So what is the cost of the over design for that high school rewiring project? Well, we don?t know the grand total, but here are the elements: (1) the cost differential between the AWG 10 and a AWG 12 neutral, (2) the cost of the No. 12 isolated ground conductor, (3) the extra cost for the orange receptacles, (4) a larger raceway to accommodate the extra conductor, and (5) the extra labor for pulling and terminating.
The question arises: why have isolated ground systems become so popular and possibly overused? Is it a plot instigated by electricians and wire manufacturers? No, I think that the name "isolated ground," even though a misnomer, sounds very appealing. A more accurate name would be "insulated ground," since the branch ground conductor is no more isolated than the phase and ground conductors are isolated. And those orange receptacles sure are impressive.
? 2001 Doug Criner
iso ?
Isolated Grounding: A Waste of Good Copper?
By Doug Criner
A Chicago-area public high school was recently rewired to add 120-V receptacles for personal computers. The designer specified isolated grounding?with those orange-colored receptacles that seem so reassuring.
Each receptacle was served by four conductors: an AWG No. 12 black (hot), a No. 10 white (neutral, or "grounded conductor"), a No. 12 green (redundant raceway ground), and a No. 12 striped green (isolated equipment ground)?all installed within a grounded, steel conduit. Let?s consider what on Earth might be going on here.
Four Conductors
The black hot wire is about the only thing that makes absolute sense. The oversized neutral is evidently based on the possibility that harmonics, generated by nonlinear loads, such as computers, can overload the neutral conductor of a 3-phase, 4-wire, wye-connected circuit. However, for a single-phase circuit, even a 120/240-V circuit with a shared neutral, it is virtually impossible for the neutral current to exceed the phase current. Therefore, there is no reason for over-sizing the neutral.
The raceway ground conductor is not a bad idea, since it provides redundancy to the ground path provided by the steel conduit. Such a redundant ground conductor, while not required by the National Electrical Code, is often specified for peace of mind in case the conduit develops loose or corroded connections. (In an isolated-ground system, a redundant raceway ground conductor is bonded to the receptacle box, but it is not connected to the ground terminal on the receptacle.)
The isolated ground conductor is connected to the ground connector on the receptacle and can then be run back to the service ground bus, unconnected to the ground bus of intermediate panels. What is the purpose of such an isolated ground system? Interestingly, you may get several different answers, depending upon whom you ask.
Purpose of Iso-Ground?
One explanation is that some manufacturers of sensitive electronic equipment "require" that their equipment be supplied by an isolated ground system. This explanation is a little weak?first, because such a system is certainly not required by manufacturers of personal computers and, second, because equipment manufacturers are not necessarily the sole authority on power distribution.
(An example comes to mind: some equipment manufacturers once "required" that their equipment be grounded to a separate building ground rod, isolated from the building?s regular electrical ground?an unsafe practice that is prohibited by the NEC. In my opinion, equipment manufacturers should themselves be "required" to design their equipment to be compatible with any power distribution system design that meets the NEC.)
Another explanation is that an isolated ground system affords greater personnel safety against shock?which is why the orange receptacles are seen in hospital rooms, right? However, the NEC does not require an isolated ground system in hospital rooms. (The NEC does require a redundant ground conductor in the hospital?s raceway but not an isolated ground. Interestingly, the NEC allows an ungrounded system in hospitals, which is the Gold Standard of shock protection, at least for the first ground fault.)
Another theory is that in the event of a ground fault, the fault current passing through the electrical raceway can raise the voltage of the raceway, and any connected equipment grounds, enough above ground potential to be a shock hazard. Studies at the Georgia Institute of Technology do not support this concern.
Some people think that an isolated ground system somehow alleviates power quality problems caused by nonlinear power supplies. Yes, computers do introduce harmonics because their power supplies chop up the sinusoidal current. Perhaps these harmonics might, in turn, cause problems to other electronic equipment. But these harmonics are propagated through the hot and neutral conductors, and no jiggering of the branch grounding conductors will prevent this.
Another justification cited for isolated grounds has to do with the effects of ground loops, those pesky things that can play havoc with low-voltage data signals. But we?re dealing here with 120-V power, not low-voltage data, and if things are installed properly, there should be no current in the grounding path, except during a ground fault?when ground loops will be the least of our worries.
Noise Suppression
The final argument, and the only one sanctioned by the NEC, is that an isolated ground system may reduce electromagnetic noise interference from appearing on the branch circuit. (In fact, the NEC permits the use of an isolated ground system only where required to reduce electromagnetic noise interference; thus, anybody who insists there is any other reason for installing isolated grounding is caught in a Catch 22?and prohibited by the code from installing an isolated ground.)
Large currents in nearby circuits can induce small, unwanted 60-Hz voltages in the grounded raceway of another circuit and the grounded cases of any plug-and-cord equipment. Possibly, some poorly isolated equipment might be sensitive to this?certainly, old-fashioned AC-DC tube-type radios, whose filaments were connected across the AC line, were prone to an annoying 60-Hz hum.
But for most situations, this theoretical concern should be negligible, unless you happen to be located next to an arc welder. To the extent that a separate, isolated ground conductor will be shielded by its steel raceway, it logically follows that current-carrying conductors in another, adjacent circuit would also be shielded. Further, induced voltages between separate circuits are unlikely to occur when the conductors of each circuit are tightly bundled, which will cause induced voltages to be self canceling. In any case, if a redundant ground conductor is pulled inside the steel conduit, and bonded to the receptacle and box, it seems likely that any 60-Hz hum would be suppressed.
At What Cost?
So what is the cost of the over design for that high school rewiring project? Well, we don?t know the grand total, but here are the elements: (1) the cost differential between the AWG 10 and a AWG 12 neutral, (2) the cost of the No. 12 isolated ground conductor, (3) the extra cost for the orange receptacles, (4) a larger raceway to accommodate the extra conductor, and (5) the extra labor for pulling and terminating.
The question arises: why have isolated ground systems become so popular and possibly overused? Is it a plot instigated by electricians and wire manufacturers? No, I think that the name "isolated ground," even though a misnomer, sounds very appealing. A more accurate name would be "insulated ground," since the branch ground conductor is no more isolated than the phase and ground conductors are isolated. And those orange receptacles sure are impressive.
? 2001 Doug Criner
electrimate
Member
- Location
- Baton Rouge, LA
I agree that isolated grounds are probably a waste of money. Better power supplies in the equipment would be a better way to address the problem.
But that is what the manufacturers of a lot of telecomm equipment do, save money on power supply filtering and state that the equipment must be powered by an isolated ground circuit.
Back to the original question. Recording studios have one big problem usually. Ground loops. They are caused by the power supplies in the equipment. Recording equipment is selected because it makes good recordings, not because it has high tech power supplies. Recording studios are often a retrofit in an existing building. Adding a single phase panel with 8 isolated circuits is a tiny investment when you consider the thousands of dollars per week of recording time that could be lost due to electrical line noise.
I helped a friend set up his small studio. I suggested runing new circuits to every room. He wanted to save money and we only ran two dedicated circuits to the tracking room - the room with the recording console. I did some recording there. When I tried to record the bass guitar tracks in another room, there was a huge ground loop problem. I was using one of the most expensive DI boxes (direct input, used for recording instruments) on the market. The ground loop was probably because the different neutral that was feeding that room. I had to run an extension cord into the tracking room and plug into the same source as the recorder to eliminate the ground loop hum.
But that is what the manufacturers of a lot of telecomm equipment do, save money on power supply filtering and state that the equipment must be powered by an isolated ground circuit.
Back to the original question. Recording studios have one big problem usually. Ground loops. They are caused by the power supplies in the equipment. Recording equipment is selected because it makes good recordings, not because it has high tech power supplies. Recording studios are often a retrofit in an existing building. Adding a single phase panel with 8 isolated circuits is a tiny investment when you consider the thousands of dollars per week of recording time that could be lost due to electrical line noise.
I helped a friend set up his small studio. I suggested runing new circuits to every room. He wanted to save money and we only ran two dedicated circuits to the tracking room - the room with the recording console. I did some recording there. When I tried to record the bass guitar tracks in another room, there was a huge ground loop problem. I was using one of the most expensive DI boxes (direct input, used for recording instruments) on the market. The ground loop was probably because the different neutral that was feeding that room. I had to run an extension cord into the tracking room and plug into the same source as the recorder to eliminate the ground loop hum.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
electrimate said:
ACK!! NO!! The ground loop was because you had, well, a loop. It has nothing to do with the neutrals. When you ran the extension cord, you get the ground from the other room, making more of a star grounding circuit. If the only connection to the grounding system is a single point, it's much harder to have a loop. Check out the Audio Cyclopedia and the Yamaha sound reinforcement handbook for discussions of signal grounds and loops.
ELA
Senior Member
- Occupation
- Electrical Test Engineer
I have spent a lot of my career dealing with " electrical noise" or EMI issues in equipment. While I agree that an Isolated ground may not eliminate problems I do understand why some people specify it.
I have worked with a number of EMC consultants and they like to state that ," ground is the sewer system of electronics".
Unfortunately the NEC requirement to earth ground equipment is often in direct conflict with keeping an electrically pristine environment. Often times one piece of equipment will conduct noise currents onto the ground wire that are then picked up by other sensitive equipment, thus causing the later to experience intermittent failures.
Equipment requiring shielded signal cables often have their shields terminated to the chassis or earth ground. The intent is to provide a "drain" for noise currents. If the ground they are connected to is polluted with noise from other equipment you can end up with more issues by terminating the shields to ground than if you left them floating.
Actually the best EMI shield is one that is terminated with 360 degree connections at each end of two interconnected metallic enclosures. In this case noise currents are prevented from entering the cable. When done in this manner there is no need to earth ground the shield. However if you do earth the shield and each piece of interconnected equipment has a PE connection now you have a ground loop which can introduce other problems.
Computers are notorious for causing ground loops when interconnected with serial ports. On RS232 serial ports the logic common is connected to the chassis and thus PE. So two computers interconnected via serial ports along with their PE connections form a ground loop. This results in data communications errors. Having an isolated ground would do nothing to help this situation. Instead the serial ports should be optically isolated to break the loop.
Having worked on a lot of EMI problems I can say that it is not a clear science. What works in one instance may not work in another. I certainly would never pretend to understand completely or over simplify the "black art" of electromagnetic compatibility.
For the sound studio I believe that an isolation transformer is the best bet. The 120/60 balanced power option even better.
I have worked with a number of EMC consultants and they like to state that ," ground is the sewer system of electronics".
Unfortunately the NEC requirement to earth ground equipment is often in direct conflict with keeping an electrically pristine environment. Often times one piece of equipment will conduct noise currents onto the ground wire that are then picked up by other sensitive equipment, thus causing the later to experience intermittent failures.
Equipment requiring shielded signal cables often have their shields terminated to the chassis or earth ground. The intent is to provide a "drain" for noise currents. If the ground they are connected to is polluted with noise from other equipment you can end up with more issues by terminating the shields to ground than if you left them floating.
Actually the best EMI shield is one that is terminated with 360 degree connections at each end of two interconnected metallic enclosures. In this case noise currents are prevented from entering the cable. When done in this manner there is no need to earth ground the shield. However if you do earth the shield and each piece of interconnected equipment has a PE connection now you have a ground loop which can introduce other problems.
Computers are notorious for causing ground loops when interconnected with serial ports. On RS232 serial ports the logic common is connected to the chassis and thus PE. So two computers interconnected via serial ports along with their PE connections form a ground loop. This results in data communications errors. Having an isolated ground would do nothing to help this situation. Instead the serial ports should be optically isolated to break the loop.
Having worked on a lot of EMI problems I can say that it is not a clear science. What works in one instance may not work in another. I certainly would never pretend to understand completely or over simplify the "black art" of electromagnetic compatibility.
For the sound studio I believe that an isolation transformer is the best bet. The 120/60 balanced power option even better.
Long winded explanation.
Long winded explanation.
The basic problem is rooted in ancient audio equipment design practices (since deprecated by AES standard 48) and has entered into the 'everyone knows' catagory of audio folklore.
The underlying problem is that the safety ground conductor on outlet A when compared with the safety ground conductor from outlet B is probably going to be at some difference in potential. This is more common in a commercial building with years of random differing electrical plant being installed, modified, removed and eroding away.
When the electric piano is plugged into outlet A, and the mixing board is plugged into outlet B in the next room, and the audio cables connected, this now provides a new ground path for those differing potentials to equalize. The problem is that the signal ground path in the audio cable is now bringing that difference current through the audio gear, and that ground current is running on a trace in the internal circuitry of the mixer and piano, only millimeters away from the trace that is carrying the signal over to the amplifier stage. Noise is induced and amplified to the quiet desperation of the sound engineer. This is a ground loop that is manifesting in a piece of gear that has the 'pin 1 problem' in it's design.
Best solution, but usually cost prohibitive, is to junk all the gear that has the pin one design fault, and replace it with good gear. Then you don't need anything special power-wise, other than enough of it.
Next best solution, and most commonly implemented is to beef up the building electrical grounding system, well beyond the minimums set in the NEC. Then provide a seperate audio power panel that all the audio gear outlets are fed from. This minimizes the differing safety ground potentials. The ground loops are still there, but since the differences are smaller, they can be more easily ignored. Misunderstandings of this dedicated audio power panel concept is what leads to the myth of 'all audio must be on the same phase'.
While there is some merit in wanting all audio power coming from the same phase, so that all gear will experience the exact same input power voltage. I submit that a decently designed power supply should be able to cope with the slightly different voltages it encounters. If the relative phase voltages are swinging so wildly that they overcome the power supplies in the equipment, then the building power system has a much more substantial problem. Trying to hide it behind single phase panelboards would be disengenous at best, and certianly would attach liability to the electrician perpetrating this.
Next thing that is commonly done by better funded operations is to feed that dedicated audio panelboard from an isolation transformer. Balanced power is simply a special case of an isolation transformer, and absent certian uncomon hazard conditions, is really a fine example of selling serpent lubricant to the gullible.
The other thing you want to do, if you cannot provide an isolation transformer, is to do your best to move electrically noisy gear to circuits that are not on the dedicated audio panelboard. This especially would be lighting dimmers, flouresent lights, copiers, laserprinters, and anything with a variable speed motor. These throw all kinds of crap onto the power supply wiring, and will leak past cheaper power supplies into the signal circuits.
To take this into the useful trick for the regular electrician. This is also probably the correct solution to all those folks buying home theater systems with twenty-dozen different expensive components. And then keep trying to solve that annoying 60 hz buzz in the sound or the hum bar in the video signal. Run in a dedicated circuit or two from the house panel, through a small isolation transformer to the system location. Beef up the building electrical ground system. Put in some blue outlets and tell them that those are special outlets that only the home theater stuff should plug into it. Should solve pretty much all the problems, as they have already had the AV guys out to go over the system a few times looking for problems. If you really want to sell them some serpent lubricant, get some of the gold plated outlets that the audiophool suppliers carry.
Back to the original poster's question. Isolated ground outlets will probably solve that particular person's noise problem. If the building has a good grounding system already in place.
--Dale
Theatrical electrician, and show power practitioner.
Long winded explanation.
The basic problem is rooted in ancient audio equipment design practices (since deprecated by AES standard 48) and has entered into the 'everyone knows' catagory of audio folklore.
The underlying problem is that the safety ground conductor on outlet A when compared with the safety ground conductor from outlet B is probably going to be at some difference in potential. This is more common in a commercial building with years of random differing electrical plant being installed, modified, removed and eroding away.
When the electric piano is plugged into outlet A, and the mixing board is plugged into outlet B in the next room, and the audio cables connected, this now provides a new ground path for those differing potentials to equalize. The problem is that the signal ground path in the audio cable is now bringing that difference current through the audio gear, and that ground current is running on a trace in the internal circuitry of the mixer and piano, only millimeters away from the trace that is carrying the signal over to the amplifier stage. Noise is induced and amplified to the quiet desperation of the sound engineer. This is a ground loop that is manifesting in a piece of gear that has the 'pin 1 problem' in it's design.
Best solution, but usually cost prohibitive, is to junk all the gear that has the pin one design fault, and replace it with good gear. Then you don't need anything special power-wise, other than enough of it.
Next best solution, and most commonly implemented is to beef up the building electrical grounding system, well beyond the minimums set in the NEC. Then provide a seperate audio power panel that all the audio gear outlets are fed from. This minimizes the differing safety ground potentials. The ground loops are still there, but since the differences are smaller, they can be more easily ignored. Misunderstandings of this dedicated audio power panel concept is what leads to the myth of 'all audio must be on the same phase'.
While there is some merit in wanting all audio power coming from the same phase, so that all gear will experience the exact same input power voltage. I submit that a decently designed power supply should be able to cope with the slightly different voltages it encounters. If the relative phase voltages are swinging so wildly that they overcome the power supplies in the equipment, then the building power system has a much more substantial problem. Trying to hide it behind single phase panelboards would be disengenous at best, and certianly would attach liability to the electrician perpetrating this.
Next thing that is commonly done by better funded operations is to feed that dedicated audio panelboard from an isolation transformer. Balanced power is simply a special case of an isolation transformer, and absent certian uncomon hazard conditions, is really a fine example of selling serpent lubricant to the gullible.
The other thing you want to do, if you cannot provide an isolation transformer, is to do your best to move electrically noisy gear to circuits that are not on the dedicated audio panelboard. This especially would be lighting dimmers, flouresent lights, copiers, laserprinters, and anything with a variable speed motor. These throw all kinds of crap onto the power supply wiring, and will leak past cheaper power supplies into the signal circuits.
To take this into the useful trick for the regular electrician. This is also probably the correct solution to all those folks buying home theater systems with twenty-dozen different expensive components. And then keep trying to solve that annoying 60 hz buzz in the sound or the hum bar in the video signal. Run in a dedicated circuit or two from the house panel, through a small isolation transformer to the system location. Beef up the building electrical ground system. Put in some blue outlets and tell them that those are special outlets that only the home theater stuff should plug into it. Should solve pretty much all the problems, as they have already had the AV guys out to go over the system a few times looking for problems. If you really want to sell them some serpent lubricant, get some of the gold plated outlets that the audiophool suppliers carry.
Back to the original poster's question. Isolated ground outlets will probably solve that particular person's noise problem. If the building has a good grounding system already in place.
--Dale
Theatrical electrician, and show power practitioner.
dalesql said:
Dale while I agree with some of your comments, "beefing up" the ground is a complete waist of time and money. While the problem is related to ground issues, “beefing up” does very little if anything at all. As you noted the problem is from minute potential differences along the path of a common EGC used with receptacles being daisy chained together on a common circuit. The ground potential differences are caused from the power supplies in each piece of equipment leaking minute currents into the EGC from the RF filter capacitors on the AC line connected L-G and N-G. The filters leak b/c of the nature of the unbalanced AC system using a grounded circuit conductor as the common return conductor and unsymmetrical imbalance with ground used as a reference point.
There are a few ways to eliminate the problem but the key to all of the techniques is forming a Single Point Ground (SPG) and incorporating dedicated AC circuits to power the various pieces of equipment. No matter how much current the equipment leaks into the EGC, when the SPG is employed with dedicated circuits, it is impossible for any ground potential voltage differences to occur. So how does one do that? Well it depends on the situation.
For the OP, they are constructing a new house, so it is very simple. Since it is wood framed construction, you just simple run dedicated quad circuits from the service panel to the point of use using NM cable, plastic boxes, and plain ole Solid Ground quad receptacles. By the very nature of the wood framed house and installation materials makes the circuit IG. It would be a complete waist of time and materials using special 4-conductor cable, conduit, and IGR. No special beefed up ground required, what ever the service has is more than adequate.
In a commercial or industrial application, it may not be possible to run dedicated circuits from the main panel where the N-G bond is made, or in other words a SPG. In that case you simple make a NEW N-G bond or create a new SPG. The only way to do that in compliance with NEC is by using an ISOLATION TRANSFORMER. Then you just repeat the above by running dedicated circuits to the point of use. Again no special beefed up ground, just a NEC compliant ground run from the Xo of the transformer to the nearest ground electrode.
If you were to use a plug-n-cord rack mounted isolation there is no need for any grounding, as the EGC supplied by the primary circuit would bond the Xo inside the transformer to create a new SPG. All that is really needed in this type of application is a single dedicated 240 circuit to plug the transformer into, making it a very inexpensive option over a hard wired premise wiring system.
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
One other point: using interconnects with balanced lines that do not use the shield as signal reference goes a long way towards reducing noise pickup. Of course, the equipment must be equipped for this, with XLR connectors being the most common type.
dereckbc said:
In new construction, or in well maintained modern commercial buildings, you would be entirely correct. But what about the 100+ year old building? or the building that someone created a new service sometime in the past, and used the water pipe as the ground. Later on, that water pipe got replaced with a PVC pipe and that water pipe upstairs no longer has path to earth ground. I see this often enough that when I suspect any grounding problem, I go and inspect the building ground system for problems.
In retrospect, instead of using the phrase beefing up the ground, what I really meant was bringing the ground up to modern standards. Last year, I worked on a place where some prior tenant was using the iron pipe of the outside storm drain as their ground connection for an electrical panel. Ground wire went out through the wall and bonded to the old pipe on the third or fourh floor. Single point grounding or setting up a mesh grounding scheme would address the ground loop issue. If the problem relates to RFI/EMI, then that ground needs a really good connection to mother earth. I'm in a fairly urban area, with lots of radio and TV transmitters, so RFI and EMI are often a component of the overall problem.
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