Datacenter
Data center grounding and the signal reference grid field guide
Bond every metal part into one network, build the signal reference grid right, and size the conductors so the whole plane sits at one potential.
Direct answer
Data center grounding and bonding ties every metal part, racks, cable tray, raised floor, conduit, and building steel, into one common bonding network at a single potential. Beyond the NEC fault-clearing ground, it adds a signal reference grid for a low-impedance reference across a broad frequency range. TIA-607 and IEEE 1100 govern the design.
Key takeaways
- Data center grounding ties every metal part (racks, tray, raised floor, conduit, building steel) into one common bonding network at a single potential.
- The smallest TIA-607 bonding conductor is generally 6 AWG copper; the mesh ties to the secondary busbar with 1/0 or larger.
- Use mesh (multipoint) bonding, not single-point: above roughly 10 MHz conductor inductance turns one path into a high impedance.
- TIA-607 hierarchy runs PBB (TMGB) to SBB (TGB) via the telecommunications bonding backbone; bonding conductor color is green.
- Bond on clean bare metal with listed two-hole lugs; a lug over paint, powder coat, or anodizing connects to nothing.
Data center grounding and bonding, defined
Data center grounding and bonding is the system that ties every piece of metal in the room into one electrically common network, so there is no voltage difference between any two surfaces the equipment or a person can touch. Grounding is the connection to earth. Bonding is the connection between parts. The data center cares about both, but the work that sets it apart from an ordinary building is the bonding.
The system does two jobs that pull in different directions. The first is the safety ground the NEC demands: a low-impedance fault path back to the source so a line-to-ground fault trips the breaker fast, and a connection to earth for lightning and surge. That is the equipment ground, and it is non-negotiable. The second job is the one the NEC does not require and the data center adds anyway. The sensitive electronics need a stable, low-impedance reference across a wide band of frequencies, and they need every chassis, cabinet, and shield sitting at the same potential so noise current has nowhere to flow.
Bond everything together well enough and there is no potential difference to drive a noise current and nothing for a fault or a surge to lift unevenly. That equipotential plane is the whole point. The companion guide on ground resistance and bonding testing covers how you prove the bonds and the earth connection after they are in. This guide is the design and the install.
Why is data center grounding more than the NEC minimum?
The NEC, NFPA 70 Article 250, gives you a grounded, bonded, fault-clearing system, and a building wired to that standard is safe. It is also not enough for a room full of high-speed electronics. Article 250 is written around the 60 Hz fault and the lightning event. It says almost nothing about the megahertz-range noise and the equipotential reference that decide whether a server farm runs clean.
So the data center treats the NEC as the floor and builds a supplemental bonding network on top of it. The reference for that supplemental work is ANSI/TIA-607 for the telecommunications bonding and grounding, and IEEE 1100, the Emerald Book, for powering and grounding sensitive electronic equipment. Neither one replaces the NEC. They sit above it. The TIA-607 busbar that serves a telecom room still bonds back to the service grounding electrode system the NEC requires.
The practical line is this. The NEC ground keeps people alive and clears faults. The supplemental bonding network keeps the electronics happy and keeps a surge from tearing across the room. A design that stops at the NEC minimum passes inspection and still leaves the owner with a noise problem and an uneven surge path nobody can see until something resets at 2 a.m.
What is the common bonding network (CBN)?
The common bonding network, the CBN, is the set of all the metal in the building that is intentionally or incidentally tied together to form one bonding network, connected to the grounding electrode system. It is the structural steel, the rebar, the metallic plumbing, the AC equipment grounding conductors, the conduit, the cable tray, the busbars, and the bonding conductors that link them. In a data center the CBN always has a mesh topology, because you want many parallel paths, not one.
Inside the computer room, the design intent is a mesh bonding network, sometimes written MESH-BN or mesh-CBN. This is a deliberate grid built into the equipment space out of the racks, the cable tray, the raceway, and a network of bonding conductors, so the whole floor sits at a uniform potential. IEEE 1100 is the reference that walks through how to build it. The mesh is what makes the difference between a room where everything is bonded and a room where everything is bonded to the same low-impedance plane.
Think of the CBN as the parent and the signal reference grid as the part of it built specifically for the equipment. Every rack, tray, and floor section bonds into the CBN, and the CBN bonds to earth through the grounding electrode system. Done right, you cannot find two points in the room with a meaningful voltage between them.
What is a signal reference grid (SRG)?
The signal reference grid, the SRG, is a grid of copper conductors, usually run under the raised floor and bonded to everything around it, that gives the equipment one low-impedance reference across a broad frequency range. It can be bare copper conductors on a grid, flat copper strap, the bolted raised-floor understructure itself where it qualifies, or in heavy cases a copper sheet. The grid is what matters, not the exact material.
Why a grid and not a single wire to ground? Frequency. A single conductor is a fine reference at 60 Hz and useless at 30 MHz, because at high frequency the conductor's inductance dominates and even a short length becomes a high impedance. Spread the reference into a mesh and the parallel paths drop the impedance and shorten the distance from any point to the nearest grid conductor. A typical install connects to the floor understructure at every fourth pedestal on a 2 ft by 2 ft floor, and that spacing keeps the conductor lengths short enough to hold a reference from DC up to roughly 30 MHz, which covers most of what the equipment puts out. IEEE 1100 treats grid density between about 2 and 4 ft as the target.
The SRG gives noise current a short, low-impedance return so it does not wander through signal cables and chassis. It contains the electromagnetic fields between source and reference instead of letting them radiate into the next rack. Its noise role mattered most in the era of unbalanced signaling, coax and RS-232. With balanced Ethernet and fiber the noise benefit has shrunk, but the equipotential job, holding the whole floor at one potential for fault and surge, has not.
Single-point vs mesh (multipoint) grounding
Old practice grounded sensitive electronics at a single point, one connection to ground per system, to avoid ground loops. That works at low frequency. It falls apart above a few megahertz, and it is why the data center moved to mesh.
Here is the physics. A single-point ground forces all the return current through one path, and at high frequency that one conductor's inductance turns it into an impedance, so different chassis end up at different potentials and the noise current you tried to control flows through the signal wiring instead. Modern digital equipment switches at 100 MHz to 300 MHz and higher. At those frequencies conductor length is the enemy, and a single ground point is the longest possible path. The IEEE 1100 guidance reflects the move: above roughly 10 MHz the case for single-point grounding breaks down and multipoint bonding to a solid reference plane wins.
Mesh, or multipoint, bonds the equipment to the grid at many points, so every path is short and the parallel combination is low impedance across the whole band. The honest caveat is that pure multipoint can create low-frequency ground loops, which is why some systems still use a controlled single-point connection inside a defined zone. For the data center floor as a whole, mesh is the answer. The single-point religion is what you unlearn.
What is TIA-607 and the telecommunications bonding backbone?
ANSI/TIA-607 is the standard that defines the bonding and grounding infrastructure for telecommunications and data spaces. It is the document a structured-cabling or data center spec points to when it calls out the busbars and the conductors that tie them together. The current revisions are TIA-607-D and the newer TIA-607-E, and the terminology changed over the versions, which trips up anyone who learned the old names.
The hierarchy is a busbar tree linked by a bonding backbone. At the top is the primary bonding busbar, the PBB, which is the connection to the electrical service grounding electrode system. From the PBB, the telecommunications bonding backbone, the TBB, runs through the building's backbone pathways and ties to the secondary bonding busbars, the SBBs, in the telecom and equipment rooms. The TBB exists to equalize potential between those rooms, so a surge or a fault does not lift one room relative to another.
If you trained on the older revisions, the PBB was the telecommunications main grounding busbar, the TMGB, and the SBB was the telecommunications grounding busbar, the TGB. The TBB kept its name. The conductor color is green, or green with a yellow stripe, so an inspector can pick the bonding system out of a tray full of cable on sight. The exact busbar sizes and the TBB sizing table live in the standard, and the project spec or the engineer can call for more than the minimum, so confirm the revision the project adopted before you cut conductor.
The bonding busbars: PBB, SBB, and the rack ground bar
Everything in the bonding network lands on a busbar somewhere, and the busbars form the tree. Get the hierarchy right and the rest of the install has somewhere to go.
The primary bonding busbar, the PBB or TMGB, is one per building, usually in the main telecom or electrical room, bonded to the service grounding electrode system with a short, heavy conductor. The secondary bonding busbar, the SBB or TGB, is one per telecom room or equipment area, fed from the PBB by the telecommunications bonding backbone and serving as the local landing point for everything in that space. Down at the cabinet, a rack bonding busbar, the RBB, is the vertical or horizontal copper bar mounted in the rack that the equipment in that rack bonds to.
Two details an inspector and a commissioning agent both check. First, the busbar is mounted on insulators standing off the wall or the rack, so it is connected to ground only through its intended bonding conductor and not incidentally through the mounting. Second, the connections are two-hole listed lugs, not single-hole, because a single bolt lets the lug rotate and loosen. Predrilled busbars come with the NEMA two-hole pattern for exactly this reason. A single-hole lug on a bonding busbar is a rookie tell and a callback waiting to happen.
Bonding the racks and cabinets to the grid
Every rack and cabinet bonds to the common bonding network, and TIA-607 wants that bond direct, not borrowed through the equipment grounding conductors of whatever happens to be plugged in. A rack that relies on a PDU's ground for its bonding is one tripped cord away from floating.
The clean method is a rack bonding busbar in the cabinet. The equipment inside bonds to the RBB with unit bonding conductors, the UBCs, and the RBB bonds down to the SRG or the mesh with a rack bonding conductor, commonly 6 AWG or larger. Where there is no RBB, each cabinet bonds to a rack bonding conductor or straight to the grid with a listed two-hole compression lug. The connection rides on bare metal: the rack's powder coat or paint gets removed under the lug, or you use a listed paint-piercing washer or a thread-forming bonding screw rated for it.
This is where most of the field failures live. Painted surfaces under lugs and missing rack bonds are among the most common findings when an inspector walks a modular or prefab data center. The lug looks bonded. The paint underneath means it is bonded to nothing. Doors and side panels on a cabinet need their own bonding jumpers too, because a hinge or a latch is not a reliable bond, and the door is what a tech touches. Bond the frame, bond the doors, bond the panels, and land it on bright metal.
Raised floor and understructure bonding
The access floor is both a structure and a candidate signal reference plane, and the bonding depends on which one it is. A raised floor is a grid of pedestals supporting panels, often with stringers bolting the pedestals together, and a bolted-stringer understructure can serve as part of the SRG where the design qualifies it. A stringerless floor, or one with loose mechanical joints, cannot be trusted as a reference and needs a dedicated copper grid under it.
Where the understructure is the grid, the bonding has to reach it consistently. Pedestals get bonded to the SRG conductors, commonly at a regular interval such as every fourth pedestal on a 2 ft floor, so no part of the floor is far from a bonded point. Where a separate copper grid is laid, it runs on roughly 2 to 4 ft centers, bonded at the crossings, and the floor pedestals tie into it.
Two field truths. A painted or anodized pedestal is not a bond, same as a painted rack, so the connection lands on clean metal or a listed clamp made for the pedestal. And the floor moves: panels lift for cabling work for the life of the building, so the bonds have to be on the structure, not on anything that gets pulled and set back. The detail covering the raised access floor itself, its load and layout, is a separate topic; here the only question is whether the metal under your feet is one bonded plane or a field of isolated posts.
Cable tray and conduit bonding
Cable tray and conduit carry the cabling and they are also metal in the room, so they bond into the CBN like everything else. The catch with tray is the joints. Tray comes in sections, and the splice plates that hold two sections together are a mechanical connection, not a guaranteed electrical one. Paint, anodizing, and a few loose bolts mean a tray run can be electrically broken every 10 ft even though it looks continuous.
So you bond across the joints. A listed bonding jumper, commonly 6 AWG, jumps each splice, or the tray is assembled with listed bonding splice plates rated to carry the bond through the joint. Then the tray run itself bonds to the CBN at intervals. Where tray is used as an equipment grounding conductor at all, it has to be listed and identified for that use, and the splices have to be made up to carry fault current, which is a higher bar than just holding the sections together.
Conduit is the same idea with different hardware. Threaded rigid conduit made up tight is generally a good bond by itself. EMT relies on its fittings, and a loose setscrew connector or a missing locknut is a broken bond, so concentric and eccentric knockouts get bonding bushings and bonding jumpers where the NEC requires them. The principle does not change across either one. A mechanical joint is not an electrical joint until you prove it.
Bonding the lightning protection and the SPD ground
Lightning protection and surge protection only work if they are bonded into the same grounding system as everything else, and the failure mode when they are not is violent. A lightning protection system, NFPA 780, with its own ground that is separate from the building's grounding electrode system creates two grounds at different potentials. A strike then drives a huge voltage between them, and that difference flashes over through whatever is in between, which is your equipment. NFPA 780 and the NEC both require the lightning system and the building grounding to be bonded together for exactly this reason.
Surge protective devices follow the same rule from the other direction. An SPD diverts transient energy to ground, and it can only hold the clamped voltage as low as the impedance of its ground path allows. Long, looped, or high-impedance SPD leads throw away the device's rating, and an SPD bonded to an island instead of the common network lifts that island during the event. The SPD installation guide covers the lead-length and clamping side of this in detail; from the grounding side the requirement is one bonded system, short paths, no islands.
The unifying idea across lightning, surge, and fault is equipotential. During the event you cannot keep the whole system at zero volts, the energy is too large, but you can keep everything rising and falling together so there is little difference across anything sensitive. That is what bonding the lightning and surge grounds into the CBN buys you. Separate grounds are not safer. They are the hazard.
Is an isolated or dedicated ground better for sensitive equipment?
No. The belief that sensitive equipment wants its own private earth, separated from the dirty building ground to keep noise out, is wrong, it is dangerous, and the standards moved away from it. A truly isolated ground builds a voltage difference between the equipment and everything around it, which is the exact noise path and shock hazard you were trying to remove.
The confusion comes from a term. IEEE 1100 describes an isolated bonding network, sometimes called an IBN, and the name misleads people. It is not isolated from the building grounding system. It is insulated so that it connects to the rest of the grounding infrastructure at one controlled point, not floated off on its own. There is always a bond back to the building ground. The NEC isolated-ground receptacle is a different and narrower thing: it gives an insulated equipment grounding conductor back to the panel, but that conductor still returns to the same grounded system. It was never permission to build a separate earth.
On the data center floor the mesh has won and the isolated-island approach is out. If a spec or a vendor still asks for a dedicated, separated ground for a piece of gear, push back and get the engineer to reconcile it with the bonding network, because installed as written it creates the potential difference it claims to prevent. The bonding-testing guide spends more time on this myth and how to catch an island with a ductor.
Conductor sizing for the bonding network
The bonding conductors are sized by the standard and the spec, and the floor under all of it is the NEC minimum. The smallest bonding conductor in a TIA-607 system is generally 6 AWG copper. Everything else sizes up from there based on its job and its length.
Working down the tree: the telecommunications bonding backbone, the TBB, is sized by its length per the TIA-607 table, starting at 6 AWG and growing as the run gets longer, because a longer conductor has more impedance to overcome. The mesh bonding network in a computer room is commonly bonded to the room's secondary busbar with a 1/0 conductor or larger, and each cabinet or rack bonds to the mesh with 6 AWG or larger. A supplementary bonding grid laid as bare copper runs 6 AWG round wire or 2 in wide copper strip, bonded at the crossings on roughly 10 ft centers, with a 1/0 connection up to the busbar.
Two rules keep the sizing honest. The bonding conductors are copper, green or green-with-yellow jacketed where insulated, and bare where they are the grid itself. And the bonding conductor that doubles as part of the fault path, like an equipment grounding conductor upsized when the phase conductors grow, follows the NEC proportional rule on top of whatever TIA-607 asks for, so the larger of the two requirements governs. These are recommended and minimum values; the project specification and the engineer can call for heavier, and where they do, the spec wins.
- TBB
- Telecommunications bonding backbone, the conductor from the PBB to the SBBs, sized by length, minimum 6 AWG
- RBC / UBC
- Rack bonding conductor to the grid and unit bonding conductor from equipment to the rack busbar
- Mesh-BN
- Mesh bonding network in the equipment room, commonly 1/0 to the busbar and 6 AWG to each rack
Connections and workmanship: exothermic, listed lugs, clean metal
A bonding network is only as good as its worst connection, and the connection is where the work gets won or lost. Two families of connection do the job. Exothermic welds, the molded copper-to-copper fusion you make with a graphite mold and a charge, give a permanent, irreversible, low-resistance bond that does not loosen and does not corrode, which is why the buried grid and the grounding electrode connections favor them. Mechanical connections, listed compression lugs and listed clamps, give a connection you can take apart, which is what you want at a busbar or a rack you will service.
The rules that separate a passing bond from a failing one are not complicated. Use listed connectors rated for the conductor and the application, and for ground and bonding terminations that means listed for grounding, not a generic lug. Land on clean, bare metal: paint, powder coat, anodizing, and mill scale all get removed under the lug, or you use a listed paint-piercing device made for it. Torque the connection to the value on the lug or the busbar, because an under-torqued bonding lug backs out under thermal cycling and a corroded or loose bond drops voltage and makes heat right at the joint.
The thing that ages a bonding system is corrosion at the dissimilar-metal connections and at anything outdoors. Copper to aluminum, copper to galvanized steel, any of it exposed to moisture, sets up galvanic corrosion that eats the bond over years. Use the right listed connector for the metals involved, apply the antioxidant the connector calls for, and keep the painted-over and corroded joints off your install, because that is the connection that reads fine on day one and opens silently in year five.
Proving the grid: resistance and bonding continuity
Installing the bonding network is half the job. Proving it is the other half, and the two measurements are different instruments answering different questions.
Ground resistance, the path from the grounding electrode system to earth, is measured in ohms with a fall-of-potential test, and a data center spec often calls for a low number such as 5 ohms or 1 ohm at the signal reference grid. Bonding continuity, the path between two metal parts, is measured in milliohms with a low-resistance ohmmeter, the ductor, which pushes real current through the joint so a corroded bond cannot hide the way it does from a multimeter's tiny test current. A bond that reads a few milliohms is solid. One that reads in the ohms, or jumps when you wiggle the lug, is a connection that will fail under fault or surge current.
On the SRG and the CBN, what you are testing is bonding, not earth resistance. You ductor the grid crossings and the bonds from racks, tray, raceway, and floor into the network, looking for low, consistent milliohm readings that prove the plane is actually one plane and not a dozen islands that happen to sit near each other. The dedicated bonding-testing guide walks the fall-of-potential method, the 62 percent rule, and the ductor in full. The design lesson here is to make every connection accessible enough to test, because a bond you cannot reach with a probe is a bond nobody will ever verify.
AI racks and high density: what changes
High-density and AI compute racks change the grounding conversation mostly through scale. A rack that used to draw a few kilowatts can now draw 40, 80, or more, with busways and large feeders running overhead, and bigger fault currents demand a fault path sized to match. The bonding has to carry what the new power distribution can deliver, which pushes the equipment grounding conductors and the rack bonds up in size.
The mesh philosophy does not change; if anything it matters more. Dense racks packed tight, liquid cooling manifolds, busway tap-offs, and the metal of the cooling distribution units all add conductive parts that have to bond into the same plane. A liquid-cooled rack brings piping into the cabinet, and that piping bonds too. The move toward direct-DC and battery distribution on some sites brings low-voltage DC buses where a small voltage drop or a poor bond is a larger fraction of the supply, so the bonding gets checked harder, not less.
The trap is treating a high-density retrofit as a power-only project. The feeders get upsized and the bonding gets left at the old rating, and now the fault path is undersized for the new fault current. When the rack density goes up, the bonding network sizing gets revisited in the same pass.
The maintenance the owner takes on
A bonding network is not install-and-forget, and the owner who treats it that way finds out during an event. Bonds loosen under thermal cycling, corrode at dissimilar-metal joints, and get disturbed every time a tech lifts a floor panel, swaps a rack, or reroutes a tray. The network that tested clean at commissioning drifts, quietly, and nothing in the room tells you until a fault or surge finds the open joint.
The maintenance is a periodic re-check of the bonds and the ground, on a cadence the operator sets, with a ductor on the meaningful connections and a fall-of-potential or selective test on the earth ground in the dry season when the soil reading is worst. The connections that get disturbed by work, rack bonds, tray jumpers, floor pedestal bonds, get re-verified after the work, not assumed. A torque check on the busbar lugs catches the ones backing out before they open.
The single best thing the installer leaves the owner is a record: what is bonded to what, with what conductor, by what connection, and what each one read at acceptance. Without it, the next person testing in year five has no baseline to compare against and no way to know whether a reading drifted or was always that way. The record is the maintenance program's starting point.
What to document
Undocumented bonding leaves every future maintainer and troubleshooter guessing at what is actually tied to what. The record answers the question that comes up during every incident and every retrofit: is this part actually bonded, to what, and how. Capture it at acceptance, while the connections are open and visible, because once the floor panels are down and the cabinets are loaded, half of it is no longer reachable to inspect.
Record each element, what it bonds to, the conductor size and type, the connection method, and the acceptance reading for that bond or ground. Tie every bond to the busbar tree so a reviewer can trace any rack back to the SBB, the TBB, the PBB, and the grounding electrode system. Where a conductor was upsized over the minimum, note why, so the next person does not undersize the replacement.
| Element | Bonded to | Conductor size | Connection type |
|---|---|---|---|
| Equipment in rack | Rack bonding busbar (RBB) | Unit bonding conductor, per equipment | Listed two-hole lug, paint removed |
| Rack / cabinet frame | SRG or mesh-BN | 6 AWG or larger (RBC) | Two-hole compression lug on bare metal |
| Cabinet doors and panels | Rack frame | Listed bonding jumper | Listed jumper, both ends |
| Rack bonding busbar (RBB) | Secondary bonding busbar (SBB) | 6 AWG or larger | Listed lug, insulated standoff |
| Secondary busbar (SBB / TGB) | TBB to PBB, and mesh-BN | Often 1/0, TBB sized by length | Exothermic or two-hole lug |
| Primary busbar (PBB / TMGB) | Service grounding electrode system | Per length, heavy | Exothermic or listed lug |
| Signal reference grid / mesh | Secondary busbar | 1/0 or larger | Listed connector at crossings |
| Cable tray section | Adjacent section and CBN | 6 AWG bonding jumper | Listed jumper or bonding splice plate |
| Raised floor pedestals | SRG / understructure | Per design interval | Listed clamp or lug, bare metal |
Common mistakes
- Using a single-point or isolated ground for high-frequency equipment, where conductor inductance makes the single path a high impedance above a few megahertz.
- Leaving racks and cabinets unbonded to the grid, or bonding them only through a plugged-in PDU's equipment grounding conductor.
- Bonding a lug over paint, powder coat, or anodizing, so it looks bonded and connects to nothing.
- Not jumpering cable tray and conduit sections across the joints, leaving a run electrically broken every few feet.
- Running the lightning protection or an SPD to a separate ground instead of bonding it into the common bonding network.
- Undersizing the bonding conductors below the TIA-607 and NEC minimums, or leaving them small after a high-density power upsize.
- Single-hole lugs on busbars and rack bonds, which rotate and loosen under thermal cycling.
- Corroded or dissimilar-metal connections with no antioxidant, which read fine at acceptance and open silently years later.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The framework spans a few documents, and naming the right one for the right point is how a submittal holds up. The NEC, NFPA 70 Article 250, governs the grounding and bonding installation and sets the minimum: the equipment grounding for fault clearing and the grounding electrode system for the connection to earth. ANSI/TIA-607, in its current revisions, defines the supplemental telecommunications bonding and grounding, the PBB and SBB busbars, the telecommunications bonding backbone, and the conductor sizing for them. IEEE 1100, the Emerald Book, is the recommended practice for powering and grounding sensitive electronic equipment, and it is the source behind the common bonding network, the mesh, the signal reference grid, and the single-point-versus-multipoint guidance.
On the surrounding topics, NFPA 780 covers lightning protection and the requirement to bond it to the building grounding system, and NEC Article 242 with UL 1449 govern the surge protective devices, both treated in depth in the companion surge guide. IEEE 80 is the substation grounding safety reference that large data center yards with their own medium-voltage gear borrow for step and touch potential. NETA acceptance testing specifications give the pass criteria a commissioning agent tests to.
Two honest cautions. Section and table numbers and even the busbar names shift between editions and TIA revisions, so confirm them against the revision the project adopted and the local code amendments before citing them on a submittal. And the project specification and the engineer's design can call for more than any of these minimums, so where the spec is stricter, the spec governs.
Units, terms, and conversions
The bonding and grounding world mixes acronyms and unit systems, and a spec, a drawing, and a vendor sheet can each use a different name for the same thing.
Ground resistance to earth is in ohms; bonding continuity is small and reads in milliohms, where 1000 milliohms is 1 ohm and a good bond is a few milliohms. Conductor size is AWG for smaller conductors and kcmil for larger ones, with mm squared on metric drawings. Grid spacing shows up in feet on most North American jobs and meters elsewhere, where 10 ft is about 3 m. The busbar names changed across TIA-607 revisions, so PBB and TMGB mean the same primary busbar, and SBB and TGB mean the same secondary busbar.
- CBN
- Common bonding network, all the building metal bonded together into one network connected to the grounding electrode system
- SRG / mesh-BN
- Signal reference grid, the grid of copper conductors giving a low-impedance reference across a broad frequency range
- PBB / TMGB
- Primary bonding busbar, one per building, bonded to the service grounding electrode system
- SBB / TGB
- Secondary bonding busbar, one per telecom or equipment room, fed by the TBB
- TBB
- Telecommunications bonding backbone, the conductor tying the PBB to the SBBs to equalize potential
- IBN
- Isolated bonding network, insulated but still bonded to the building ground at one controlled point, not a separate earth
- Equipotential
- The condition where bonded parts sit at the same potential, so no noise, fault, or surge current is driven between them
FAQ
What is a signal reference grid (SRG)?
A signal reference grid is a grid of copper conductors, usually under a raised floor and bonded to everything around it, that gives data center equipment one low-impedance reference across a broad frequency range. The mesh keeps conductor paths short, holding a usable reference from DC to roughly 30 MHz.
What is the common bonding network (CBN)?
The common bonding network is all the metal in a building, structural steel, conduit, cable tray, busbars, racks, and bonding conductors, intentionally tied together into one network connected to the grounding electrode system. In a data center it has a mesh topology so the whole room sits at one potential.
Single-point or mesh grounding: which does a data center use?
Data centers use mesh, or multipoint, bonding. Single-point grounding works at low frequency but fails above a few megahertz, where conductor inductance turns the one path into a high impedance. Modern equipment switches at 100 to 300 MHz, so short, many-pathed mesh bonding to a reference plane wins.
What is TIA-607?
ANSI/TIA-607 is the standard for telecommunications bonding and grounding, defining the busbar hierarchy and conductors for data and telecom spaces. It specifies the primary bonding busbar, the secondary bonding busbars, and the telecommunications bonding backbone tying them together. Current revisions are TIA-607-D and TIA-607-E; older versions used the TMGB and TGB names.
Does an isolated or dedicated ground reduce noise for servers?
No. A separate, isolated earth builds a voltage difference between equipment and its surroundings, which is the noise path and shock hazard you meant to avoid. The IEEE 1100 isolated bonding network is insulated but still bonded to the building ground at one controlled point. Mesh bonding has replaced the isolated-island approach.
How do you bond a server rack to the grid?
Bond the rack directly to the signal reference grid or common bonding network with a 6 AWG or larger conductor and a listed two-hole lug on bare metal, not through a plugged-in PDU. Use a rack bonding busbar for the equipment inside, and add jumpers on doors and panels.
What size conductor bonds a data center rack and the mesh?
Under TIA-607 the minimum bonding conductor is generally 6 AWG copper. Each rack or cabinet bonds to the mesh with 6 AWG or larger, and the mesh bonding network commonly ties to the room's secondary busbar with a 1/0 conductor or larger. The project specification can require heavier.
Why must lightning protection be bonded to the building ground?
A lightning protection system on a separate ground creates two grounds at different potentials, and a strike drives a large voltage between them that flashes over through your equipment. NFPA 780 and the NEC require the lightning system bonded to the building grounding system, so everything rises and falls together during the strike.
Is the raised floor understructure a valid signal reference grid?
Sometimes. A bolted-stringer access floor with solid metal-to-metal joints can serve as part of the signal reference grid where the design qualifies it. A stringerless or loosely jointed floor cannot be trusted and needs a dedicated copper grid underneath. Bond pedestals to the grid on the design interval, on bare metal.
People also ask
Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.