Neutral Bar and Ground Bar Sizing: Positions, Wire Range and Bonding by Service Size, for Panelboards, Subpanels and Transfer Switches
Sep 10, 2026
Summary: Size a neutral or ground bar by three numbers: the number of terminations plus 25 percent spare, the largest conductor it must land (small positions are 14 to 4 AWG, large lugs 6 AWG to 350 kcmil or bigger), and the main neutral or grounding electrode conductor from NEC Table 250.66 or 250.102(C)(1). At the service, the neutral bar is bonded to the enclosure with the main bonding jumper and the ground bar may be the same bar; in every subpanel and separately derived system after that, the neutral bar must be isolated from the enclosure and a separate ground bar bonded to it, per NEC 250.24(A)(5) and 250.142(B). One conductor per hole unless the bar is marked for two; the bar must be listed to UL 67 or UL 467 and marked for the conductor material.
Count the positions
| Panel | Typical terminations | Bar |
|---|---|---|
| Residential subpanel, 12 to 20 circuits | 15 to 25 neutrals, same grounds | Two 14 to 4 AWG bars, 22 to 30 positions each, plus a 2 AWG to 2/0 main lug |
| Commercial 42-circuit panelboard | 42 neutrals, 42 grounds, plus feeders | Neutral: 50 positions with 250 or 350 kcmil main lug; ground: 42 to 50 positions |
| Transfer switch, 200 A | Neutral pass-through plus 2 to 4 feeders | 5 to 8 position 4 AWG to 300 kcmil bar |
| Solar combiner or inverter ground bar | One per string plus EGC | 15 to 42 position AL9CU bar, 14 to 4 AWG |
| Telecom or data center ground bar | Two-hole lugs on NEMA spacing | Copper busbar, 1/4 x 2 or 1/4 x 4 in, drilled on NEMA pattern |
Add 25 percent spare positions; a full bar is the first thing an inspector flags on a panel addition. Where more conductors than positions exist, add a second bar bonded with a listed jumper or bar-to-bar strap; never double-land conductors in a single hole unless the bar is marked for two of that size.
Match the wire range
| Bar position type | Range | Lands |
|---|---|---|
| Small screw position | 14 to 4 AWG (some 14 to 6) | Branch circuit neutrals and grounds, up to 4 AWG |
| Medium lug | 6 AWG to 2/0 or 14 to 1/0 | Subpanel feeders, GEC to a rod (6 AWG), water pipe bond |
| Large main lug | 6 AWG to 350 kcmil, or 2 AWG to 600 kcmil | Service neutral, main GEC, large feeders |
| Stud or two-hole pad | Compression lug sizes | Data center and industrial ground bars |
The main neutral lug must accept the service neutral; a 200 A service on 4/0 aluminum needs a 350 kcmil-capable lug. Bars marked AL9CU accept aluminum; copper-only bars (marked CU) do not. Both are common; read the marking.
Main conductor sizes that drive the lug
| Service or feeder | Neutral (typical) | GEC to rod (250.66(A)) | GEC to water pipe or Ufer (Table 250.66) | Supply-side bonding jumper (250.102(C)) |
|---|---|---|---|---|
| 100 A, 2 AWG Cu | 2 to 4 AWG | 6 AWG Cu | 8 AWG Cu | 8 AWG Cu |
| 200 A, 4/0 Al or 2/0 Cu | 4/0 Al or 1 AWG Cu | 6 AWG Cu | 4 AWG Cu | 4 AWG Cu |
| 400 A, 500 kcmil Cu or 600 Al | 350 kcmil Cu | 6 AWG Cu | 1/0 Cu | 1/0 Cu |
| 800 A, 2 x 500 kcmil Cu | 2 x 350 kcmil | 6 AWG Cu | 2/0 Cu | 2/0 Cu |
| 1200 A, 3 x 500 kcmil Cu | 3 x 350 kcmil | 6 AWG Cu | 3/0 Cu | 3/0 Cu |
Rod GEC never needs to exceed 6 AWG copper (250.66(A)); Ufer GEC never needs to exceed 4 AWG (250.66(B)). The lug that lands them is usually the medium position.
Bonded or isolated
| Location | Neutral bar | Ground bar | NEC |
|---|---|---|---|
| Service equipment (first disconnect) | Bonded to enclosure by the main bonding jumper | May be the same bar or a separate bar bonded to enclosure | 250.24(B), 250.28 |
| Subpanel in the same building | Isolated from enclosure; bonding screw removed | Separate bar, bonded to enclosure, EGC from the feeder | 250.24(A)(5), 250.142(B) |
| Detached building fed by a 4-wire feeder | Isolated | Bonded, plus a grounding electrode at the building | 250.32(B) |
| Generator or transformer as a separately derived system | Bonded at one point only, the system bonding jumper, usually at the source or first disconnect | Bonded | 250.30(A) |
| Transfer switch, solidly connected neutral | Pass-through, not bonded | Bonded | 250.30, 702 |
| Transfer switch, switched neutral | Switched; generator neutral bonded at generator | Bonded | 250.30(A)(1) |
The most common panel inspection failure in the country is a bonded neutral in a subpanel. The second is grounds and neutrals sharing a bar in a subpanel. An add-on ground bar kit with its own screws bonded to the enclosure is the fix for both.
Listing and installation
- Bars are listed to UL 67 (panelboards) or UL 467 (grounding); add-on kits are listed for the panel families named on the package or are generic UL 467 bars mounted with the supplied machine screws into the enclosure.
- One conductor per position unless marked; some bars permit two 14 or 12 AWG grounds in one hole when so marked, never two neutrals.
- Torque per the bar marking, typically 20 lb-in for 14 to 10 AWG screw positions and per the lug torque chart for the main lugs.
- Aluminum bars accept copper conductors; tin-plated aluminum is standard. Copper bars are specified for data centers and where copper is required by the owner.
Quick answers
Can neutrals and grounds share a bar in a subpanel? No. In a subpanel the neutral bar is isolated and grounds land on a separate bar bonded to the enclosure (NEC 250.24(A)(5)).
How many neutral positions do I need? One per circuit plus 25 percent spare; two conductors per hole are not permitted for neutrals.
What size lug for a 200 A service neutral? One that accepts 4/0 aluminum or 2/0 copper; a 6 AWG to 350 kcmil AL9CU main lug is the standard choice.
Do I bond the neutral in a generator transfer switch? Only if the generator is a separately derived system with a switched neutral; with a solidly connected neutral, the neutral passes through unbonded and is bonded only at the service.
Conversions Tech stocks aluminum neutral and ground bars from 3 to 190 positions, 14 AWG to 750 kcmil, ground bar kits and neutral lugs, plus copper busbar for data center and telecom grounding. Panel shops: blanket pricing and cross-reference on the panel shop page.
