Grounding, bonding and surge protection
Ground bars, exothermic connections, lugs and earthing kits, plus the surge protective devices that clamp transients before they reach equipment.
What is the difference between grounding and bonding, and where does surge protection fit?
Grounding and bonding do two different jobs and are routinely conflated. Grounding establishes a reference to earth; bonding ties metal parts together so fault current has a low-impedance path back to its source and a protective device actually operates. The equipment grounding conductor is not the neutral, and treating it as one is a recurring and dangerous error. Surge protection is a separate layer again, rated by where it sits relative to the main overcurrent device.
The 2 families in this category
36 documented configurations in total, with indicative lead times from 4 to 10 weeks. Each family links to its own reference page.
| Family | How it is specified | Lead time | Indicative band | Standards |
|---|---|---|---|---|
| Ground Bars & Kits18 documented configurations | Type: TMGB / TGB / Rack Kit Holes: 12 / 20 / 36 Material: Copper / Tinned Cu |
~4 wk | $22 – $640 /ea | UL 467 IEEE 1100 |
| Surge Protective Devices18 documented configurations | Type: Type 1 / Type 2 kA: 50 / 100 / 200 Voltage: 208V / 480V / 600V |
~10 wk | $180 – $5K /ea | UL 1449 |
What to settle in the specification
Telecom bonding to ANSI/TIA-607
Data center bonding for IT and telecom follows ANSI/TIA-607: a primary bonding busbar (TMGB) bonded to the building’s electrical grounding, secondary busbars (TGBs) in each telecom space, and a bonding backbone between them. Specify busbar hole patterns for the lugs that will actually land on them.
Connection method
Exothermic welds, compression connectors and mechanical connectors are all used. Below-grade and inaccessible joints are usually exothermic or compression connectors qualified for that duty (IEEE 837). Accessible joints can be bolted. Every product should be listed to UL 467.
SPD type by location
UL 1449 types are defined by where the device sits. Type 1 can go on the line side of the service disconnect, Type 2 on the load side, and Type 3 at the point of use. Installation rules are in NEC Article 242 (Article 285 in editions before 2020).
SPD ratings that matter
Compare voltage protection rating (VPR), nominal discharge current (In) and the short-circuit current rating (SCCR). The SCCR must meet the available fault current where the SPD is installed, which is set by the transformer impedance upstream.
Material and environment
Tinned copper busbars and connectors resist corrosion better than bare copper in humid or corrosive environments. Insulated standoffs keep a busbar isolated from the wall it’s mounted on, so the only bond is the one that was designed.
Common questions
What is the difference between a TMGB and a TGB?
Under ANSI/TIA-607, the TMGB (primary bonding busbar) is the main bonding point for telecommunications, bonded to the building’s electrical service grounding. TGBs (secondary bonding busbars) sit in each telecom room and connect back to the TMGB through the telecommunications bonding backbone.
What is the difference between Type 1 and Type 2 surge protective devices?
Under UL 1449, a Type 1 SPD can be installed on the line side of the service disconnect, and a Type 2 SPD is installed on the load side, usually at a switchboard or panelboard. Type 3 devices are point-of-use protection further downstream.
Should grounding connections be exothermic or compression?
Both are used. Exothermic welds form a permanent molecular bond and are common below grade. Compression connectors qualified to IEEE 837 are also accepted for below-grade use. Mechanical, bolted connectors suit accessible locations where connections may need to be inspected or changed.