Equipment Grounding Bar for a Data Closet?

Question

I'm building out a data closet for my home office using a Leviton structured media cabinet (plastic). Some of my equipment (routers, switches) have lugs for external grounds and use 'brick' power supplies without ground plugs.

I found a nice 6" grounding bar pre-drilled with tapped holes from an industrial supplier, and I'm planning to mount it in the cabinet. My question concerns connecting it to the home's grounding system. As part of the upgrades I have an accessible metal junction box with EMT running all the way back to the service entrance within about 8 feet of the data cabinet. Would it be acceptable practice to take a green #12 stranded wire, crimp ring terminals onto each end, and connect one end to the ground screw in the junction box and the other end with a screw to one of the tapped holes in my new grounding bar?

Answer 1

First to bond the common bonding bus in the media cabinet to the Grounding Electrode System of your homes electrical Service. To do that run a large conductor or bond strap with the same cross sectional area as the conductor from the media cabinet single point bonding busbar to the service equipment. The National Electrical Code only requires #10 American Wire Gauge (AWG) but I would suggest a bare number 4 AWG copper wire or strap of equivalent cross sectional area if you are able to pay the higher cost for the strap. The reason for using strap instead of a round conductor of the same cross sectional area as the strap is that the physical shape of a strap causes it to have a lower impedance to the passage of current during and electric anomaly such as a lightning discharge, contact between the secondary distribution conductors which supply your home with power and higher voltage wires, and current surges or voltage spikes on the utility system's distribution conductors.

At the Service Equipment enclosure connect the bonding conductor to one of the Grounding Electrode Conductors from your Service Equipment. That is often the main panel that contains the first point at which you can disconnect all power from the houses electrical system. That very first Breaker, fused pull out, or Fused Switch is the Service Disconnecting Means. That will bond the common point bonding busbar to the Grounding Electrode System of your homes electrical system.That is done to do the all important job of keeping the conductive pathways, such as Ethernet cables, as near as possible to the same voltage during a voltage spike event. If a large voltage difference develops in between the communications equipment and the Service Equipment Grounding Electrode Conductors it may equalize through your communications equipment by forcing more current through their circuits and components than they can carry without being destroyed.

[All electrical and electronic systems function because they contain magic smoke! If you let the magic smoke escape you will have to buy replacement equipment that still has it's magic smoke or install new components in your damaged equipment to replace the components from which the magic smoke has escaped. No Magic Smoke No function.]

The bonding conductor provides a much lower impedance pathway between the Grounded/(Neutral) Conductor of the Electrical utility's supply. With all of the Grounded Conductors of every circuit powering things in your home connected to that grounded conductor you want to keep the voltage as nearly the same on the grounded Conductors everywhere in your home's wiring system.

That is were this next question comes in. What do you have for electrical power receptacles in your structured media cabinet? Whatever form the mounting of those receptacles takes you want them to be protected from high voltages in the conductors supplying that circuit. That is done by installing high quality surge protection devices at the media cabinet and bonding the Equipment Grounding Conductor (EGC) of the electrical circuit to the single point bonding busbar. That is done by drilling a hole through which you can install a 10/32 bronze or copper bolt from the inside of the receptacles enclosure to the portion of your media cabinet were your single point bonding busbar is mounted. On the inside of the receptacle enclosure the EGC of the branch circuit supplying the receptacles gets bonded to this machine screw. On the outside of the receptacle enclosure you connect a bonding conductor or strap to the single point bonding busbar. This bonding connection keeps the EGC of the branch circuit as close as possible in voltage to the bonding terminals of the communications equipment. Keeping the voltage difference as low as practicable prevents the flow of destructive amounts of current through the communications equipment.

Install a high quality surge protector on every cable which enters the cabinet. That includes twisted pair cable like the ones used for wired Ethernet and coaxial cable if that is used for cable television. With Coaxial cable it is important to use Surge protectors and not just cable shield bonding blocks.

You must use a coaxial cable protector instead!

The protector provides voltage difference limiting while the shield bond connection only keeps the exterior protective braid near ground potential.

Installing surge protection for every conductive pathway into or out of your media cabinet gives you the highest likelihood of avoiding equipment damage.

Consider installing point of use protection at every device served by the communications wiring and power wiring. You do that by using plug strip protectors that also have protection for the communications media that connects to the same device. If 2 types of communications media connect to one device use a protector which protects both communications paths and the power.

I worked as a communications wireman for several years doing construction and installation coordination of remote communications equipment shelters. I also was part of 2 different crews who installed communications systems in large building such as the AOL server farm in Dulles, Virginia. My answers are based on my understanding of Soares book on Grounding, Motorola Standard R56 Standards and Guidelines for Communication Sites and National Fire Protection Association Standard 70: 2020 National Electric Code.

Tom Horne

Answer 2

The proper way is to run another single green or uninsulated wire back to your entrance panel disconnects ground. This will be where the building ground, ground rods, and electrical grounds are all connected. Condulet grounds do not work well with electronics. Over time the joints will increase in resistance causing a grounding failure. I have been down this path several times in office and factories, the direct wire always works. I also over size it and use copper.

Answer 3

Let me suggest that you run the # 10 green inside the Electrical Metallic Tubing back to the panel and bond it to the EMT at both ends.

That will minimize the impedance of the EMT while providing a redundant Equipment Grounding Conductor for the branch circuit. It needn't be larger than the #14 EGC required for a 15 ampere circuit or the 12 AWG for a 20 ampere branch circuit. Notice the Lay In Lug. Turn that straight out from the inside wall of the enclosure. Let the locknut that is on the EMT connector do it's job of holding the connector in place and bonding the connector to the wall of the enclosure by making it up wrench tight. screw the bonding bushing down as far as it will go and then turn it so that you can use both the lug terminating screw and the bonding screw of the bushing easily. The tighten the bonding screw which will make a good electrical connection. Lay the EGC in the lug and tighten the lug terminal screw.

What I was suggesting as a bonding conductor for the common bonding busbar in the media center is #4 bare or black insulated stranded wire. A bonding conductor can be terminated to a Grounding Electrode Conductor or to the Grounded/Neutral Conductor busbar inside the service equipment enclosure. The bonding conductor may not be green in color because green is reserved for Equipment Grounding Conductors (EGC)s run with individual circuits or added to existing circuits under 250.130(C). Because of the particular job you would be installing the bonding conductor to do it should leave the media cabinets and enter the Service Equipment Enclosure through a Kenny Clamp.

That bonds the Bonding conductor to the enclosure at each end so that the enclosure will not behave as a choke and add reactance to the bonding circuit thus raising the impedance of the Bonding Conductor equalization pathway needlessly. The reason for the suggested size of the intersystem bonding conductor is to keep the grounded conductors of the electrical service and the communications circuits and equipment as close to each other in voltage as possible. It takes a difference of potential, measured in volts, to cause destructive current flow. I used to express it to new people thus. "We don't care if they get up to thousands of volts as long as they're dancing to the same music and holding each other really tightly. NO SUBSTANTIAL DIFFERENCE = NO DESTRUCTIVE CURRENT FLOW.

Tom Horne