Grounding and bonding computer electronics

[don_resqcapt19]

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.

While such systems are permitted by 640.9(A)(2), the actual systems are covered by Article 647

 

[don_resqcapt19]

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?

The IG rule permits that grounding conductor to run back to the location of the system or main bonding jumper, whichever applies, while the standard EGC must terminate where in the enclosure where the branch circuit originates.
How you actually install the IG is a design issue...as long as it provides the required fault clearing path, the code does not care.

 

[PowerdT]

You run both a EGC and an IG.

That is going to be very hard on existing infrastructure.

 

[don_resqcapt19]

That is going to be very hard on existing infrastructure.

There is no real reason to install an isolated ground. It really does not have any function in the real world.

 

[PowerdT]

There is no real reason to install an isolated ground. It really does not have any function in the real world.

You mentioned long time ago you installed IG to an industrial distributed control system which prevents the equipment from frying.

We know that the fault protection system which has the branch circuit with EGC in same raceway also provide protection to personal and equipment.

So are you saying IG is not going to help with the noise? If this doesn’t solve, probably isolator transformer is what helps

 

[mtnelect]

When I was doing traffic signal work for the County of Los Angeles, we started converting our controllers from electromechanical to digital. We were installing "170 Controllers" which were all solid state. Our electrical service started on a utility pole and went underground to the controller where we installed a second ground rod. After installing several cabinets, we started getting calls that the intersections were going on "Flash". I discovered that there was a difference in potential between the two ground rods. So, I disconnected the second ground rod at the controller cabinet and pulled a grounding conductor back to the service, and that corrected the problems.

 

[jim dungar]

There is no real reason to install an isolated ground. It really does not have any function in the real world.

Most installations need a separate/dedicated grounded conductor, but our industry slanged this into being the same thing as the extremely rare 'isolated ground'.

 

[PowerdT]

Most installations need a separate/dedicated grounded conductor, but our industry slanged this into being the same thing as the extremely rare 'isolated ground'.

What do you mean by separate/dedicated? Are you referring no connection to transformer Xo?

 

[jim dungar]

What do you mean by separate/dedicated? Are you referring no connection to transformer Xo?

No.
A conductor that has a path directly from the outlet back to a common bonding point cor the source, such as the neutral point of a Wye transformer. As opposed to a path that contains different materials and multiple connection, such as with a metal raceway connected to building steel.

Many dedicated circuits in a home wired with NM are actually separate/dedicated/isolated grounds.

 

[LarryFine]

When I have done IG installations, I ran a single IG conductor for everything on a given circuit, splicing it as I would a regular EGC, except otherwise keeping it insulated from ground as one would a neutral.

 

[PowerdT]

No.
A conductor that has a path directly from the outlet back to a common bonding point cor the source, such as the neutral point of a Wye transformer. As opposed to a path that contains different materials and multiple connection, such as with a metal raceway connected to building steel.

Many dedicated circuits in a home wired with NM are actually separate/dedicated/isolated grounds.

What if this common bonding point at the source is busbar that is used to bond other SDS, metal pipe or structural steel. Does it apply to bond the IG to this common busbar? I feel like it is some thing whether you do it at N-G or at common main busbar

 

[PowerdT]

When I have done IG installations, I ran a single IG conductor for everything on a given circuit, splicing it as I would a regular EGC, except otherwise keeping it insulated from ground as one would a neutral.

You splice because it’s for outlets. If you have more than one computer cabinets that are fed from 30A breaker each. Would you bring 12AWG IG and terminate to busbar so that u can bond from there ? I tho the min required wire is 6AWG

 

[don_resqcapt19]

You mentioned long time ago you installed IG to an industrial distributed control system which prevents the equipment from frying.

We know that the fault protection system which has the branch circuit with EGC in same raceway also provide protection to personal and equipment.

So are you saying IG is not going to help with the noise? If this doesn’t solve, probably isolator transformer is what helps

I said the installation of the isolated grounding system as specified by the manufacturer fried the equipment. When we modified it to comply with the NEC, the equipment frying stopped. There is no evidence that the isolated grounding system in compliance with the NEC helps with anything. Probably a spec that was originally written by the copper development association

Yes, I am saying that there is no evidence that the isolated ground serves any purpose with they types of equipment that are in use now. At one time when you had communications circuits that had connections to earth at both ends, they may have provided some benefit, but even that is in question.
If you actually have an electrical noise issue, the best solution would be the 120 volt circuit that has 60 volts to ground mentioned in post #12. See Article 647.

 

[don_resqcapt19]

What if this common bonding point at the source is busbar that is used to bond other SDS, metal pipe or structural steel. Does it apply to bond the IG to this common busbar? I feel like it is some thing whether you do it at N-G or at common main busbar

The code does not really care where you connect it, but permits it to run back to the location of the main or system bonding jumper, which ever you hit first.

 

[PowerdT]

Thank you everyone for your input in this thread. Much appreciated