Isolated Ground Outlets (for computers) to eliminate Ha

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JJWalecka

JJWalecka

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Do you install Isolated Ground outlets ( for computers) to eleminate Harmonics? How does this work? Every Isolated Outlet, that I have ever installed, derived from a branch circuit that was feed from a panel with a separate isolated ground bar that eventually tied into the grounding electrode conductor. I was told the only way to get a true Islotated ground was to drive a separate ground bar or create a "clean ground" through a Transformer. Is this true. I read briefly about series filters and shunt filters. Thank you for your time and effort.

Justin
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

I think the main reason for isolated ground outlets was to prevent the equipment (i.e. computer) from becoming part of a ground loop. If the computer is grounded at one outlet, and the printer is grounded at another outlet, and there is a printer cable with a grounded sheild tied to the computer and the printer, then you have a ground loop.

But I don't see any problem with a ground loop if the building is wired properly. Add an extra bond between the neutral and the ground, and then it could become a problem.

For the most part, i think isolated ground outlets are a waste. Modern electronics have modern power supplies. The power can go off for a fraction of a second (enough to see the lights flash), but my computer doesn't even shut down. Yet, we are supposed to believe that a cash register can't work right if it sees a millivolt signal on the ground. And the power supplies don't even use the ground, just the neutral and hot.

Steve
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

Justin there are allot of myths out there and allot of old requirements that have been added on too to keep them going. first a grounding conductor cannot have any effect on harmonic current. as the harmonic current is developed between the hot and neutral of the circuit supplying the load that is creating it. There can be filters or inductors that can shift this harmonic current off to the grounding conductor to relive it off the neutral but this can open another can of worms as it will cause this noise to appear on the grounding and also allow current to flow on the grounding conductors which is not a good thing. Connecting a grounding conductor to an isolated grounding electrode will not do anything for this and will not only violate the NEC but create a very bad electrocution hazard as any equipment that is connected to this ground has a ground fault, the resistance of the electrode is too high to open a breaker or fuse, and will bring all that is connected to it up to the circuit voltage. all grounding conductors "MUST BE CONNECTED TO THE SERVICE GROUNDED CONDUCTOR" (neutral) for a low impedance fault path back to the source to facilitate the operation of the OCPD that is protecting the circuit.
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

Q1. Do you install Isolated Ground outlets ( for computers) to eliminate Harmonics? How does this work?

A1. IGR cannot possible eliminate harmonics, so it does not work. The only possible use for an IGR is a possible means of keeping common mode noise from entering the EGC circuit. It has no other purpose. Its effects in order are: 1. No effect. 2. Makes the problem worse. 3. Desired effect. Do not be confused about the IGR, it cannot remove or filter any common mode noise as there are no passive or active circuits involved.

Statement: ?Every Isolated Outlet, that I have ever installed, derived from a branch circuit that was feed from a panel with a separate isolated ground bar that eventually tied into the grounding electrode conductor.

Comment: this is one of the correct ways to derive a IGR

Q3 and Statement: ?I was told the only way to get a true Isolated ground was to drive a separate ground bar or create a "clean ground" through a Transformer. Is this true?

A3. Only a half truth and half myth. The myth part is driving a rod isolated from the ground electrode system would not comply with NEC requirements and would put personnel and the equipment at great danger. The truth part is transformers and some high-end UPS systems will remove or filter out common mode noise to the tune of 140 decibels (a ratio of 100,000,000,000,000:1) in some cases. These two systems are separately derived systems that establish a new N-G bond point. From this new point, a IGR can then be used to prevent common mode noise from entering the circuit via a single point ground. As long as the single point ground is not corrupted by comming in contact with any grounded objects, no common mode current can flow to develop a common mode voltage (noise)
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

Dereck,

Can you provide some info on getting 140 db isolation. I deal with a lot of high end and I'm not really prepared for this subject if it comes up. And 140 is impressive.
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

A typical stepdown/isolation transformer provides about 90 db. To get 140 you need to use a special shielded isolation transformer or dual conversion UPS.
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

So, can I get something out of a box to achieve this?
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

Originally posted by physis:
So, can I get something out of a box to achieve this?
Click to expand...
Yes. At least on a small scale from say 500 VA up to 5 KVA. There are several manufactures that make isolatin transformers that you just simply plug into a wall then plug your equipment into the box. Most of it available from high-end A/V manufactures like Monster, Fuhrman, and others. The best I know of that makes both consumer and industrial uses balanced power systems (120/60) called Equi-Tech. Try this for a start http://www.equitech.com/
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

Steve66, Hurk27, and Dereckbc thank you very much for clearing that up.


Justin
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

There are 3 purposes for isolated ground receptacles and wiring:

1. The original coaxial cable Ethernet interconnected equipment grounds. The idea was to keep building wiring ground faults from burning up the Ethernet. I still cannot figure out how an open neutral in a service does not blow up the cable TV.

2. As mentioned above, prevention of ground loops that act as antennas for noise, radio frequency interference, and so forth.

3. For certain sensitive applications such as magnetic resonance imaging the equipment ground MUST be shielded from picking up radio stations and so forth. The MRI room has to be grounded at a single point as an isolated ground appliance. The room is made out of steel and is insulated from the building steel, metal studs, and so forth.
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

Mr. mc5w,
I see your up early this morning.I no one has offered it up yet,welcome to the MHE form sir.
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

I have to agree with Dereck, I've know IGR to just eliminate noise, and not cure harmonics. Harmonics are problem with the equipment itself, and can not be corrected with outside equipment. I believe IGR is for equipment that is sensitive to voltage flucuations like computer, or sound equipment.

What do you all think of TVSS being used in conjunction? :)

[ March 21, 2005, 10:58 AM: Message edited by: lady sparks lover ]
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

Originally posted by lady sparks lover:

What do you all think of TVSS being used in conjunction? Lady:)
Click to expand...
It's not too late to jump in, and your question is valid.

It depends on what kind of TVSS you are referring too, parallel or series.

Parallel units use SAD's, MOV's, and Gas Tubes. All these devices are passive, and by definition of passive means they do nothing. They only turn on for very short periods of time during a transient condition. And when they do trigger they basically short out. So they are not useful for filtering of any kind during normal operation.

Series units may or may not contain reactive filter components like reactors, inductors, and capacitors in addition to the SPD's (SAD, MOV, etc). There big draw back in series units is they must be rated for a prescribed load current since they are series. I have not seen many on the market.

Does that help?
 
Re: Isolated Ground Outlets (for computers) to eliminate Ha

By the way, the last time that I had to fix an open neutral in a service, the water supply was from a well. I still cannot figure out how the cable TV line did not burn up.

One thing that I had to do was to temporarily bond the copper tube that came in from the well casing. This provided more voltage stability until I could lay a temporary #2 copper ceutral on the ground and have Ohio Edison hook it up.

The repair was a bit expensive because I had to put in a 200 amp construction service. The new underground service had to go right where the old service was because there was only 3 to 4 feet between the driveway and the property line. Got the old service wrapped around the digging bar of the trencher twice!

An extra expense was that Summit County, Ohio has just outlawed direct burial services. Too many people, including this one, had too many instances of the Tree Root Circuit Breaker Method. In fact, this homeowner planted a spruce trees directly over his old service lateral.
 
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