Grounding and bonding computer electronics

[PowerdT]

I came across to few facilities that they ground computer electronics equipment with isolated grounding from the service entrance.

I thought it’s code violation per NEC. What do you guys think?

 

[infinity]

IG's are typically run either to the point where the MBJ is located in the service or to the X0 of a transformer. If they ran it all the way back to the service it's probably done correctly if all of the IG rules are followed.

 

[PowerdT]

IG's are typically run either to the point where the MBJ is located in the service or to the X0 of a transformer. If they ran it all the way back to the service it's probably done correctly if all of the IG rules are followed.

I see maybe I misunderstood IG. So what you are saying. Let’s see example- you have transformer N-G bond that GEC is bonded to main busbar. Are you saying if the IG is bonded to this busbar is correct?

 

[hbiss]

I see maybe I misunderstood IG. So what you are saying. Let’s see example- you have transformer N-G bond that GEC is bonded to main busbar. Are you saying if the IG is bonded to this busbar is correct?

An Isolated Ground is a separate insulated conductor (usually green/yellow) that runs from the ground screw on an IG receptacle all the way back to the service panel ground bar. Done properly that means through any sub panels and down 10 floors if necessary.

Contrary to opinions I have heard here, each IG receptacle must have its own ground conductor home run back to the service panel ground bar. You can't run one home run and tap off of it. That would cause noise and ground currents to circulate among the connected devices.

But the good news is IG receptacles are almost never used anymore. Iso ground might have been useful back four decades ago when IT equipment was interconnected by serial communications like RS-232 that contained a ground conductor that was connected to the connected device's chassis ground, essentially tying all chassis grounds together. Adding another path from the power receptacle grounds almost guaranteed ground loop problems. But today, ethernet networking effectively isolates connected devices from each other making iso grounding unnecessary. And of course, WiFi totally isolates everything electrically.

The only use these days might be with some audio installations.

-Hal

 

[infinity]

I see maybe I misunderstood IG. So what you are saying. Let’s see example- you have transformer N-G bond that GEC is bonded to main busbar. Are you saying if the IG is bonded to this busbar is correct?

Here's what a typical IG system would look like when there is a transformer involved.

 

[masterinbama]

common in the 80's. but they were rarely done properly. hardly any i ran across were done even close to infinitys diagram

 

[infinity]

common in the 80's. but they were rarely done properly. hardly any i ran across were done even close to infinitys diagram

I agree. We would see them in every office building and they were rarely installed correctly. This was the existing IG connection for all of the system IG-EGC's in a post office that we were modernizing. The red conductor went directly to the IG bus in the panel.

 

[masterinbama]

I agree. We would see them in every office building and they were rarely installed correctly. This was the existing IG connection for all of the system IG-EGC's in a post office that we were modernizing. The red conductor went directly to the IG bus in the panel.

View attachment 2566415

Dismantled many like this.

 

[PowerdT]

From what I have seen in these facilities, none of them are done correctly. All they have is ground rod near the electronics and bond to telecom busbar and that’s it. No green/yellow wires back to the Transformer Xo

 

[Speedskater]

Contrary to opinions I have heard here, each IG receptacle must have its own ground conductor home run back to the service panel ground bar. You can't run one home run and tap off of it. That would cause noise and ground currents to circulate among the connected devices.

Just the opposite is true.
The purpose of an IG circuit is to prevent noise, leakage, ground & lost Neutral currents from other circuits using your signal, data & control cables as a path back to the main panel Neutral.
An IG circuit circuit should use the same length Hot, Neutral & EGC wires.
An analog signal IG circuit should be designed so that the pathways from it's IG receptacle to receptacle is as short as practicable. The idea is to keep all the units chassis at about the same potential.

 

[PowerdT]

An IG circuit circuit should use the same length Hot, Neutral & EGC wires.
An analog signal IG circuit should be designed so that the pathways from it's IG receptacle to receptacle is as short as practicable. The idea is to keep all the units chassis at about the same potential.

How about in a situation where you have two SDS systems where 480V is your main and you have another 208V step down transformer.

Your electronics are fed from 208V so does that mean you need to run the IG circuit back to the 480V GEC?

U can not tap or splice IG so, can you terminate IG circuit from GEC to busbar inside electronics room?

 

[tortuga]

Every time I have done IG, wich is very few times, the IG was just like a 2nd EGC and was run with and spliced when the circuit conductors spliced.
They land on a floating ground bar in the panel, which has wire back to the transformer like pictured in post 5.
Except most if not all of the IG systems I did were 60/120V.
There is still quite a bit of noise on a EGC to this day, some occupancy sensors still use the ECG as a return conductor for their little internal power supply.

 

[don_resqcapt19]

How about in a situation where you have two SDS systems where 480V is your main and you have another 208V step down transformer.

Your electronics are fed from 208V so does that mean you need to run the IG circuit back to the 480V GEC?

U can not tap or splice IG so, can you terminate IG circuit from GEC to busbar inside electronics room?

There are no rules that say you cannot tap or splice the IG conductor.

The IG is only run back to the location of the main or system bonding jumper that supplies the circuit that supplies the equipment. If the 208 is supplied by a transformer it will go back to the location of the system bonding jumper for that transformer. However the grounding and bonding requirements will result in that being tied to the building grounding electrode system.

 

[PowerdT]

Every time I have done IG, wich is very few times, the IG was just like a 2nd EGC and was run with and spliced when the circuit conductors spliced.
They land on a floating ground bar in the panel, which has wire back to the transformer like pictured in post 5.
Except most if not all of the IG systems I did were 60/120V.
There is still quite a bit of noise on a EGC to this day, some occupancy sensors still use the ECG as a return conductor for their little internal power supply.

Does that mean you size based on the sub panel size for EGC or can be for example in this case if the electronics is on 30A breaker can bring 10AWG IG EGC ?

Also so IG is not GEC correct?

 

[don_resqcapt19]

Does that mean you size based on the sub panel size for EGC or can be for example in this case if the electronics is on 30A breaker can bring 10AWG IG EGC ?

Also so IG is not GEC correct?

The IG is sized per Table 250.122, just like any other equipment grounding conductor, unless the specs call for a larger size.
it is not a grounding electrode conductor, it is an isolated equipment grounding conductor, but an more correct name would have been insulated equipment grounding conductor as the word isolated results in a lot of confusion.

 

[PowerdT]

The IG is sized per Table 250.122, just like any other equipment grounding conductor, unless the specs call for a larger size.
it is not a grounding electrode conductor, it is an isolated equipment grounding conductor, but an more correct name would have been insulated equipment grounding conductor as the word isolated results in a lot of confusion.

Ok. If i understand all this facilities that bond 1/0AWG to independent rod or building steel are doing it wrong.

The electronic are protected already with EGC run with the feeder when/if fault occurs. To bring IG to telecom busbar and feed #6AWG to few cabinets will help improve noise

 

[don_resqcapt19]

Ok. If i understand all this facilities that bond 1/0AWG to independent rod or building steel are doing it wrong.

The electronic are protected already with EGC run with the feeder when/if fault occurs. To bring IG to telecom busbar and feed #6AWG to few cabinets will help improve noise

Yes they are doing it wrong and in violation of the requirements of the NEC.

The isolated equipment grounding conductor is still a fault clearing conductor and must follow all of the rules that apply to the normal equipment grounding conductor, except that they are permitted to be run back to the location of the main or system bonding jumper.

There is no evidence that the IG is effective and at least one study said the made the problem worse, helped solved the problem, or there was no change in about equal proportions.
A number of years ago we installed an industrial distributed control system. The manufacturer insisted on a completly isolated ground for their system. When we had thunderstorms in the area, they had board failures, and they asked us to prove their ground was completely isolated and we did while telling them that that isolation was the problem. The third thunderstorm season they let us tie the IG ground to the electrical ground together at a single point and the problem went away.
Where there are thunderstorms in the area, they can create a large voltage difference between the two grounding electrodes. This potential shows up on the equipment between the parts that are bonded to the electrical grounding system and those that are bonded to the isolated grounding system. A single point bond between the two systems eliminates the issue.

 

[tortuga]

For the handful of IG systems I was involved with the goal was to to eliminate hi noise voltage/current from the branch circuit equipment ground, such as ballasts and occupancy sensors. Not to create a second path to earth.
We use a 60/120V transformer so that the 120V IG receptacles were fed from 2 pole breakers. Each leg was hot with 60V to ground potential. These are used for recording studios, film and broadcast editing rooms, and AM radio transmitters that still use balanced and un-balanced audio cabling. I believe most of the benefits were due to the 60V to ground. Its covered in article 640.

 

[PowerdT]

The isolated equipment grounding conductor is still a fault clearing conductor and must follow all of the rules that apply to the normal equipment grounding conductor, except that they are permitted to be run back to the location of the main or system bonding jumper.

When you say IG has to follow same rules to normal EGC, size wire based on 250.122 and must be run with the feeders. How can you accomplish this with IG that has to go back to the transformer Xo, unless this is exception?

If you have like 5 or more sensitive electronics, do you pull IG for each or how can you do it?

 

[infinity]

When you say IG has to follow same rules to normal EGC, size wire based on 250.122 and must be run with the feeders. How can you accomplish this with IG that has to go back to the transformer Xo, unless this is exception?

You run both a EGC and an IG.