Installing a ground bar in an electrical panel is a short job with a long consequence. Mounted correctly, the bar gives every equipment grounding conductor (EGC) in the cabinet a solid metallic path back to the source, so a fault trips the breaker instead of energizing the enclosure. Mounted incorrectly — one sheet-metal screw, one layer of paint left under the foot, one missing bonding screw — the same bar looks finished and performs like nothing at all. This guide walks through selecting, mounting, bonding, terminating and verifying a ground bar, with the code references and torque discipline that inspectors actually check.
Everything below assumes North American panel practice under NFPA 70 (the NEC). If you work under IEC/BS/AS-NZS rules, the mechanical steps are largely the same but the bonding arrangement differs; check your local standard and your authority having jurisdiction (AHJ) before energizing anything.
A ground bar is a listed terminal bar with multiple positions where you land equipment grounding conductors and bonding jumpers. It is not a current-carrying part during normal operation. It exists so that when a live conductor touches metal — a worn cable inside a motor, a loose hot screw in a box — the fault current has a low-impedance path back to the source, and the overcurrent device opens fast enough to clear it.
That path only works if every link in it is metallic and continuous: conductor to terminal, terminal to bar body, bar body to enclosure or bonding jumper, and back to the source. This is why what a busbar actually is matters less for instalers than its failure modes — a bar that carries current poorly during a fault is worse than no bar, because it looks complete.
Under NEC 250.8(A), equipment grounding conductors, grounding electrode conductors and bonding jumpers must terminate by one of eight listed methods. Two of them matter here: terminal bars (250.8(A)(2)) and machine-screw fasteners that engage at least two threads or are secured with a nut (250.8(A)(5)). Note what is not on that list: ordinary sheet-metal screws. NEC 250.8(B) separately rules out connections that depend solely on solder.
Gather everything before you open the panel, so you are not reaching across a live cabinet for a file.
One planning note: many inspectors expect at least 20% spare terminal capacity left over after you land every existing and planned circuit. A bar that is full on day one forces the next technician to stack conductors or leave a circuit ungrounded, and both are worse than spending a few dollars on a longer bar.
Turn off the main breaker. Verify with a non-contact tester, then confirm with your multimeter between each phase and the neutral — test your meter on a known live source first, then re-test it after, so you know the meter itself worked. In a main panel, the service-entrance lugs above the main breaker stay live even with the breaker off. Nothing protects those conductors except distance and your own discipline. If the work brings your hand or a tool near them, stop and bring in a licensed electrician.
Panels are built with specific mounting-hole patterns, and “universal” ground bars are not a safe assumption. Cross-referencing the bar to the panel brand and type (the panel label usually lists approved accessory kits) removes the temptation to drill new holes — which risks striking conductors behind the backplane and compromises the enclosure.
Beyond fit, check these parameters on the bar or its datasheet:
| Parameter | What to check | Why it matters |
|---|---|---|
| Ways (terminal count) | Current circuits plus at least 20% spare | Avoids future double-lugging and ungrounded additions |
| Conductor range | Minimum and maximum AWG, stranded vs solid | A conductor outside the listed range will not clamp reliably |
| Material rating | Cu only, or Cu/Al with anti-oxidant compound | Direct aluminium terminations need a bar identified for them |
| Conductors per terminal | Bar marking allows two, or one only | NEC 250.8 permits multiple only when the terminal is identified for it |
| Terminal torque | Printed value from the bar manufacturer | NEC 110.14(D) requires tightening to the manufacturer’s specification |
| Mounting hardware | Machine screws, engaged at least two threads | Sheet-metal screws are not an approved grounding method |
Brass bars with nickel-plated surfaces are common in this role because they resist the oxidation that raises joint resistance over years of thermal cycling. A brass bridge-type grounding bar suits cabinets that need three to fifteen positions on a compact footprint, while a double-row screw grounding bar handles higher circuit counts without growing the bar’s length.
Most manufacturers pre-punch or pre-drill mounting positions on the enclosure backplane, sometimes covered by a knockout you tap out with a screwdriver. Use them. They place the bar outside the wiring gutters, clear of the branch-circuit busbar stabs, and within reach once conductors are routed.
A location is wrong if it requires a custom hole, sits inside the bend radius of existing conductors, or forces EGCs to cross live parts on their way in. In a crowded main panel, also confirm that adding the bar will not block the panel’s listed wiring space — fill is a compliance issue as much as a neatness one.
Powder coat and paint are insulators. NEC 250.12 requires nonconductive coatings such as paint, enamel and lacquer to be removed from threads and contact surfaces, or the connection to be made with fittings designed so removal is unnecessary. In practice you either scrape the contact pad down to bright metal, or fit an external-tooth star washer under the screw head and let the teeth bite through the coating as you torque.
Then take the file to any burrs left by knocking out the mounting knockout. A sharp edge inside a panel is a long-term insult to conductor insulation, especially on the bare-copper EGCs you are about to route to this exact spot.
Set the bar on the prepared position and start the screws by hand to avoid cross-threading. If you are using a screw-terminal grounding bar with an insulating cover, confirm which part of the assembly is intended to touch bare metal — covered designs often rely on a designated bonding point rather than the whole body.
Tighten the mounting screws with real force. In a metal enclosure the bar must be bonded to the cabinet: the cabinet itself is part of the equipment grounding path. Where the bar is fitted on insulated standoffs — common in control panels where an isolated ground is specified — the bar instead receives a dedicated bonding jumper sized for its function, landed as its own listed connection.
Route bare copper or green-insulated EGCs to the bar along the panel’s sides, keeping them out of the busbar area. Strip each conductor to the length the bar’s wire guide implies — enough that no insulation sits under the screw, not so much that bare copper extends past the terminal. Insert fully, then tighten.
One conductor per terminal unless the bar is explicitly marked for more. This is where many field installations fail inspection: the same connection that looks tidy with two wires under it was listed and tested with one.
Neutrals do not belong on this bar and EGCs do not belong on the neutral bar. NEC 408.40 requires the equipment grounding terminal bar to be bonded to the metal cabinet, and prohibits terminating EGCs on the neutral terminal bar (with the narrow exceptions in 250.142 for services and separately derived systems). If you are unsure which bar in front of you is which, read our breakdown of the difference between a neutral bar and a ground bar before landing anything.
NEC 110.14(D) requires terminals to be tightened to the torque values specified by the manufacturer, using a calibrated tool where the specification calls for it. There is no single correct number to memorize: a #14 terminal position and a #2 position on the same bar can have different values, and two brands of bar with the same wire range routinely differ.
The numbers circulating online for “typical” ground bar torque should be treated as nothing more than a sanity check. Read the value off the bar marking, the panel’s label, or the kit instructions, set your torque driver to it, and work every terminal. Loose terminations are the most common cause of the heating failures described in our guide to why busbar and terminal connections overheat — the failure starts at the weakest joint, not at the conductor.
Before you close the cover, get this right, because it determines what every later measurement should read. In service equipment — the main disconnect — neutral and ground are bonded at a single point through the main bonding jumper (usually a green screw or a strap). In a downstream subpanel they must be isolated: the neutral bar floats on insulated standoffs, and the ground bar bonds to the cabinet.
| Condition | Main / service panel | Subpanel |
|---|---|---|
| Neutral-to-ground bond | Present, via main bonding jumper | Removed; bonding screw or strap not installed |
| Ground bar to enclosure | Bonded metal-to-metal | Bonded metal-to-metal |
| Neutral bar to enclosure | Bonded | Isolated on standoffs |
| Expected N–G continuity | Continuity present, low resistance | No continuity (open) |
Neutral conductors also have their own rule worth remembering while you are in here: NEC 408.41 requires each neutral conductor to terminate in an individual terminal. Two neutrals sharing one point risks disturbing another circuit’s neutral when one is removed later.
With the main breaker still off and the panel confirmed dead, set your multimeter to the lowest resistance range and test:
Those resistance figures are field-practice expectations, not NEC limits — the Code does not set a numeric pass value for this test. Treat them as a screen for gross errors: an open reading where continuity belongs, or continuity where isolation belongs, is a definite fault to chase down before restoring power. Your AHJ and the panel manufacturer’s instructions remain the authority.
Finish with a visual check — every conductor seated, no stray strands, no insulation pinched, cover screws reinstated — then re-energize and label the panel directory.
| Mistake | What actually goes wrong | Correct approach |
|---|---|---|
| Mounting with sheet-metal screws | Shallow self-cut threads lose continuity under vibration and heat cycling; not a permitted method under 250.8(A) | Machine screws engaging at least two threads, or secured with a nut |
| Bar mounted over paint | Coating insulates the bar from the cabinet it must bond to | Scrape to bare metal or fit toothed bonding washers per 250.12 |
| Two conductors per terminal | Joint was listed and tested for one; the second is unproven | Use a terminal identified for multiple conductors, or add capacity |
| EGC landed on the neutral bar | Violates 408.40 | Land EGCs only on the equipment grounding terminal bar |
| Bar left unbonded in a metal cabinet | No fault return path; enclosure can become energized | Bond bar to cabinet, or fit a listed bonding jumper |
| Terminals tightened “by feel” | Under-torqued joints heat; over-torqued ones crack or strip | Torque to the manufacturer’s printed value under 110.14(D) |
| No spare capacity | Next circuit gets double-lugged or left ungrounded | Specify at least 20% more ways than today’s circuit count |
Yes, when the enclosure has the space and the added bar does not obstruct listed wiring space. Every bar you install must still satisfy the same bonding requirement: it has to be electrically connected to the metal cabinet or to the equipment grounding conductor feeding the panel. Adding a second bar is common when the original runs out of terminal positions.
In a metal cabinet, yes — NEC 408.40 requires an equipment grounding terminal bar to be bonded to the cabinet. The exception is the intentionally isolated case, such as an isolated-grounding arrangement built to a specific design, where the bar is insulated from the cabinet and grounded at a defined single point instead.
Avoid it. Panels are not designed for random penetrations: you risk striking conductors behind the backplane, and you compromise the enclosure’s structural integrity and listed construction. Use the manufacturer’s pre-punched positions, or the mounting pattern the panel label specifies.
Count every branch circuit EGC you terminate today, add the circuits you plan to add, then choose a bar with roughly 20% more terminal positions than that sum. The bar’s conductor range also has to cover the smallest and largest EGC you land, and its listing has to cover aluminium if any of your grounding conductors are aluminium.
In a subpanel that reading is correct and desirable — it means the neutral is properly isolated. In a main panel it means the main bonding jumper is missing or loose, or your new bar is not making metal-to-metal contact with the enclosure. Do not fabricate a bonding jumper; check for the bonding screw or strap supplied with the panel and install the correct part.
A ground bar is a simple part doing unforgiving work. Match it to the panel, mount it on bright metal with listed hardware engaged at least two threads, keep one conductor per terminal unless the bar says otherwise, torque to the manufacturer’s number rather than intuition, and verify continuity before the cover goes back on. Get the main-panel versus subpanel bonding decision right and everything else follows.
Working to a specification rather than a one-off repair? Bars are available in defined way counts, conductor ranges and custom drilling patterns — specify them against your circuit schedule rather than adapting whatever is on the shelf.
