isolated ground
- Thread starter bench892
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Re: isolated ground
Bench: I am the wrong one to answer your question. I am the only one in the world who does not consider a transformer as a separately derived system. I call them transformers.
If you ask can a transformer supply both an isolated ground and non-isolated receptacle, the answer is yes it can supply both. The non-isolated ground can terminate at the transformer neutral/ground. The isolated ground must terminate at the single point ground for the premises.
Bench: I am the wrong one to answer your question. I am the only one in the world who does not consider a transformer as a separately derived system. I call them transformers.
If you ask can a transformer supply both an isolated ground and non-isolated receptacle, the answer is yes it can supply both. The non-isolated ground can terminate at the transformer neutral/ground. The isolated ground must terminate at the single point ground for the premises.
- Location
- Massachusetts
Re: isolated ground
One thing though, do you have the locations misplaced?
I have always been taught to bring the IG to the XO of the transformer serving that branch circuit.
Bob
Bennie I was wondering how you would answer this one?
One thing though, do you have the locations misplaced?
I have always been taught to bring the IG to the XO of the transformer serving that branch circuit.
Bob
Re: isolated ground
The section 250.146(D) The only applicable derived system would be a generator, not a transformer.
Connecting to the X-O of a transformer is two point grounding. There would be a different potential on the service ground point, and the transformer ground point, if connected according to the popular interpretation of a separately derived system.
[ June 19, 2003, 05:52 PM: Message edited by: bennie ]
The section 250.146(D) The only applicable derived system would be a generator, not a transformer.
Connecting to the X-O of a transformer is two point grounding. There would be a different potential on the service ground point, and the transformer ground point, if connected according to the popular interpretation of a separately derived system.
[ June 19, 2003, 05:52 PM: Message edited by: bennie ]
Re: isolated ground
There should be an isolated ground conductor, dedicated, for each power supply. The isolated ground should be dead ended at the equipment. If the power supply is not isolated from the enclosure, the isolated ground is not effective.
The metal conduit is the conventional equipment ground.
There should be an isolated ground conductor, dedicated, for each power supply. The isolated ground should be dead ended at the equipment. If the power supply is not isolated from the enclosure, the isolated ground is not effective.
The metal conduit is the conventional equipment ground.
Re: isolated ground
My purpose of starting the thread about the history of grounding is to determine where the interpretation of a separately derived system became a transformer.
The reference in my 1908 book...Refers to "isolated plants" This later was changed to "systems with no external connections", then to "separately derived systems".
This subject has always been in the grounding article of the NEC.
An isolated ground conductor, and a non-isolated ground conductor, should terminate at the same reference point. This is possible on a generator source, but not on a power transformer that is not the service distribution system.
A source for a premises wiring system is all inclusive, this does not imply part of the system.
A premises transformer is a component of the premises wiring system according to article 100 Definitions. Therefore a transformer, other than a source for the entire premises wiring system, is a transformer nothing else.
My purpose of starting the thread about the history of grounding is to determine where the interpretation of a separately derived system became a transformer.
The reference in my 1908 book...Refers to "isolated plants" This later was changed to "systems with no external connections", then to "separately derived systems".
This subject has always been in the grounding article of the NEC.
An isolated ground conductor, and a non-isolated ground conductor, should terminate at the same reference point. This is possible on a generator source, but not on a power transformer that is not the service distribution system.
A source for a premises wiring system is all inclusive, this does not imply part of the system.
A premises transformer is a component of the premises wiring system according to article 100 Definitions. Therefore a transformer, other than a source for the entire premises wiring system, is a transformer nothing else.
Re: isolated ground
Bennie, this is a subject I do not see eye-to-eye with you. No disrespect intended.
Here is my point of view. Lets take any power source and make an isolated ground for it. The power source can be anything like a service entrance, isolation transformer, battery plant, UPS, generator, etc. To make an IG you have to establish a ground window. The ground window is a location (usually a ground bar or Xo) that separates the isolated ground plane from the integrated ground plane. The integrated ground plane is where all the metallic parts form multiple loops, and are multi-grounded to the electrode system like a grid.
Now lets assume we are going to install a 480 VAC 3-phase delta input, 208Y/120 output transformer that we want IG installed on the feeder and branch circuits. We need to bond the output of the transformer to some kind of ground electrode to be code compliant. So for this design we choose to bond the neutral at the first disconnect device. So we run an GEC from the building steel or service ground electrode, makes no difference which by code, to the neutral bus in the disconnect device. We then install a bonding jumper from the neutral bus to ground bus, and install another bonding jumper from the ground bus to an isolated ground bus. By doing this we have installed a ground window inside the disconnect device, and established both an integrated ground plane and isolated ground plane. Now from the disconnect device we can run both EGC?s (integrated ground plane conductor), and IG?s (isolated ground plane conductors) to feeder and branch circuits as needed. This ground window forms the SPG, not the service ground. The service ground is in the integrated ground plane. The isolated ground plane is can be down stream or wherever we want it.
Here is the point. If the power source is SPG to the integrated ground plane, then it does not matter what common mode currents are flowing or what voltages are developed. The grounded conductor has a single bonding point to the electrode. All the noise in the integrated ground plane is reference to the grounded conductor at the single point. Therefore the ungrounded conductors are in phase and in common mode reference with the noise. If you were to take an oscilloscope and reference its ground to the IG buss then look at the grounded conductor and ungrounded conductors you would not see any noise, it?s irrelevant. Now as long as you do not corrupt the IG circuit downstream via multi-ground, you cannot inject any common mode noise or current other than brute force EMF/RFI.
This is the basic principle used in most telephone switching offices and radio transmission sites. Even equipment manufactured for home use like HAM radio gear and PC?s use this principle. It?s the DC power supply built into them that make the SPG via the step down transformer supplying the DC rectifiers. It?s the power source that forms the SPG not necessarily the service entrance.
Bennie, this is a subject I do not see eye-to-eye with you. No disrespect intended.
Here is my point of view. Lets take any power source and make an isolated ground for it. The power source can be anything like a service entrance, isolation transformer, battery plant, UPS, generator, etc. To make an IG you have to establish a ground window. The ground window is a location (usually a ground bar or Xo) that separates the isolated ground plane from the integrated ground plane. The integrated ground plane is where all the metallic parts form multiple loops, and are multi-grounded to the electrode system like a grid.
Now lets assume we are going to install a 480 VAC 3-phase delta input, 208Y/120 output transformer that we want IG installed on the feeder and branch circuits. We need to bond the output of the transformer to some kind of ground electrode to be code compliant. So for this design we choose to bond the neutral at the first disconnect device. So we run an GEC from the building steel or service ground electrode, makes no difference which by code, to the neutral bus in the disconnect device. We then install a bonding jumper from the neutral bus to ground bus, and install another bonding jumper from the ground bus to an isolated ground bus. By doing this we have installed a ground window inside the disconnect device, and established both an integrated ground plane and isolated ground plane. Now from the disconnect device we can run both EGC?s (integrated ground plane conductor), and IG?s (isolated ground plane conductors) to feeder and branch circuits as needed. This ground window forms the SPG, not the service ground. The service ground is in the integrated ground plane. The isolated ground plane is can be down stream or wherever we want it.
Here is the point. If the power source is SPG to the integrated ground plane, then it does not matter what common mode currents are flowing or what voltages are developed. The grounded conductor has a single bonding point to the electrode. All the noise in the integrated ground plane is reference to the grounded conductor at the single point. Therefore the ungrounded conductors are in phase and in common mode reference with the noise. If you were to take an oscilloscope and reference its ground to the IG buss then look at the grounded conductor and ungrounded conductors you would not see any noise, it?s irrelevant. Now as long as you do not corrupt the IG circuit downstream via multi-ground, you cannot inject any common mode noise or current other than brute force EMF/RFI.
This is the basic principle used in most telephone switching offices and radio transmission sites. Even equipment manufactured for home use like HAM radio gear and PC?s use this principle. It?s the DC power supply built into them that make the SPG via the step down transformer supplying the DC rectifiers. It?s the power source that forms the SPG not necessarily the service entrance.
Ed MacLaren
Senior Member
Re: isolated ground
There is actually no such thing as an "isolated" EGC in the strict sense of the word, because they all must be bonded together, and to ground, at the main distribution point, in any case.
By using a "dedicated" EGC for each sensitive load, at least it won't have to carry fault currents associated with ground faults in other loads.
A metallic raceway system, or metal-sheathed cable system in a building can actually act like a large antenna to pick up electro-magnetic "noise". Because the insulated (isolated) EGC is not bonded to the receptacle mounting means, box, or yoke, it won't pick up any noise at that point. It is permitted to be kept isolated (insulated) from the raceway system, and equipment enclosures, as far back as the main distribution center for the facility, but no further. At that point, it must be bonded to the grounded (neutral) conductor, like any other EGC.
Ed
[ June 20, 2003, 12:22 AM: Message edited by: Ed MacLaren ]
There is no simple answer to your question. The answer depends on what degree of isolation is required/desired. And there is some controversy as to how effective they are.
There is actually no such thing as an "isolated" EGC in the strict sense of the word, because they all must be bonded together, and to ground, at the main distribution point, in any case.
By using a "dedicated" EGC for each sensitive load, at least it won't have to carry fault currents associated with ground faults in other loads.
A metallic raceway system, or metal-sheathed cable system in a building can actually act like a large antenna to pick up electro-magnetic "noise". Because the insulated (isolated) EGC is not bonded to the receptacle mounting means, box, or yoke, it won't pick up any noise at that point. It is permitted to be kept isolated (insulated) from the raceway system, and equipment enclosures, as far back as the main distribution center for the facility, but no further. At that point, it must be bonded to the grounded (neutral) conductor, like any other EGC.
Ed
[ June 20, 2003, 12:22 AM: Message edited by: Ed MacLaren ]
Re: isolated ground
A service can supply both isolated grounds and non-isolated.
The purpose of the isolated ground conductor is not concerned with fault current. The normal equipment ground is for that purpose.
The purpose of an isolated ground is to avoid sharing ground conductors with another device.
The isolated ground will avoid common-impedance coupling that can impact the operation of some equipment.
The common-impedance coupling is created by line filter current flow in the ground conductor.
A service can supply both isolated grounds and non-isolated.
The purpose of the isolated ground conductor is not concerned with fault current. The normal equipment ground is for that purpose.
The purpose of an isolated ground is to avoid sharing ground conductors with another device.
The isolated ground will avoid common-impedance coupling that can impact the operation of some equipment.
The common-impedance coupling is created by line filter current flow in the ground conductor.
- Location
- Massachusetts
Re: isolated ground
The metal case of the utilization equipment is connected to the IG ground.
Think of a PC plugged into an IG outlet, if the PC power supply faults to ground it is the IG ground that will clear the fault.
As far as the NEC is concerned the IG is for fault clearing.
The metal case of the utilization equipment is connected to the IG ground.
Think of a PC plugged into an IG outlet, if the PC power supply faults to ground it is the IG ground that will clear the fault.
Re: isolated ground
Iwire, you have made a point most people do not realize about IG. Utilization equipment like a PC is not made for IG circuits. I have never seen a four-wire power plug. To make IG effective you have to make sure the utilization equipment is completely isolated from planned and incidental contact with any grounded objects or cables.
This is why it should not be used in areas like data centers. In a data center the routers, modems, servers, etc are mounted in equipment racks that are bolted to the concrete floor and interconnected with cables with ground and grounded conductors all in which corrupt the IG. It?s almost impossible to keep everything isolated except in a few very well planned and installed projects where it is required. Where it is required it is not to keep noise out as much as it is to keep lightning and external faults from flowing through the equipment.
Iwire, you have made a point most people do not realize about IG. Utilization equipment like a PC is not made for IG circuits. I have never seen a four-wire power plug. To make IG effective you have to make sure the utilization equipment is completely isolated from planned and incidental contact with any grounded objects or cables.
This is why it should not be used in areas like data centers. In a data center the routers, modems, servers, etc are mounted in equipment racks that are bolted to the concrete floor and interconnected with cables with ground and grounded conductors all in which corrupt the IG. It?s almost impossible to keep everything isolated except in a few very well planned and installed projects where it is required. Where it is required it is not to keep noise out as much as it is to keep lightning and external faults from flowing through the equipment.
Re: isolated ground
Bob: I stand corrected. I should have stated...The impedance of an isolated ground conductor is higher than a normal ground conductor.
The primary purpose is for voltage reference. A fault may trip the breaker or burn clear. The high impedance design is not focused on fault clearing, it is a side effect.
Bob: I stand corrected. I should have stated...The impedance of an isolated ground conductor is higher than a normal ground conductor.
The primary purpose is for voltage reference. A fault may trip the breaker or burn clear. The high impedance design is not focused on fault clearing, it is a side effect.
Re: isolated ground
Interconnected computers should not be on IG circuits. The high impedance ground makes line filters less effective.
The effects of switching creates voltage spikes on the interconnection. These spikes can destroy input logic circuits.
Another point; Unless equipment is dead ended for ground purposes, the IG makes a ground loop.
Interconnected computers should not be on IG circuits. The high impedance ground makes line filters less effective.
The effects of switching creates voltage spikes on the interconnection. These spikes can destroy input logic circuits.
Another point; Unless equipment is dead ended for ground purposes, the IG makes a ground loop.
- Location
- Massachusetts
Re: isolated ground
It kills me that the powers that be in this area do not see this.
They pay me for IG work and then plug in the rack mount equipment and make it all a waste of money.
Somewhere someone has been sold a bill of goods on this IG bull****.
Like those that are sure they need IG outlets in a wood frame house.
Bob
Dereckbc this happens more offten than not.
It kills me that the powers that be in this area do not see this.
They pay me for IG work and then plug in the rack mount equipment and make it all a waste of money.
Somewhere someone has been sold a bill of goods on this IG bull****.
Like those that are sure they need IG outlets in a wood frame house.
Bob
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: isolated ground
Bennie
That's because when the washing machine is grounded it causes the iron in the water to go to the nearest ground, I.E. the dirt LOL
Bennie
That's because when the washing machine is grounded it causes the iron in the water to go to the nearest ground, I.E. the dirt
LOL - Status