Neutral bar terminations are generally limited to one grounded conductor per hole. The rule exists because the terminal geometry clamps one conductor squarely and two unevenly, and because removing one conductor from a doubled terminal disturbs a circuit that is supposed to stay connected. A crowded bar is a panel that needs more terminals, not more conductors per hole.
Why grounded conductors get the strict treatment
Grounded conductors carry current in normal operation, so a poor termination heats exactly as a poor hot termination would. But there is a second reason specific to neutrals. If two circuits share a terminal and someone loosens it to remove one circuit, the other circuit loses its neutral. Losing a neutral is not merely an inconvenience; on a shared-neutral arrangement it can put loads in series across the full line-to-line voltage, and on any circuit it leaves the conductor floating at whatever potential the load presents. Keeping one conductor per terminal means one circuit at a time is affected by any work.
Equipment grounding conductors are treated differently
Here is the asymmetry that surprises people. Many bars are listed to accept more than one equipment grounding conductor per terminal, and the bar or the panel documentation states how many and of what sizes. That is permitted because grounding conductors do not carry current normally, so heating is not the concern, and because temporarily disconnecting several does not de-energise or destabilise anything. The permission comes from the listing of the specific bar, not from a general rule, so read the panel label. Never assume the reverse permission applies: a bar listed for multiple grounds is not thereby listed for multiple neutrals.
How bars get crowded
The same way breakers get double-tapped: circuits are added over the years without anyone adding terminals. Tandem breakers make it worse, because two circuits arrive in a position that has one neutral hole nearby. Subpanels installed without a separate grounding bar produce the other common version, where neutrals and grounds share the neutral bar and everything is doubled. That arrangement is wrong twice over: the conductors should be on separate bars in a subpanel, and the neutrals should have one hole each. Both faults tend to appear together because they come from the same shortcut.
Adding terminals is the fix
Most panels accept an accessory grounding bar kit that mounts to the enclosure, and fitting one frees a large number of holes on the neutral bar by moving every equipment grounding conductor to where it belongs. That is usually enough. Where neutral terminals themselves are short, some panels accept an additional listed neutral bar, which must be installed per the panel instructions and bonded or isolated as appropriate for whether the panel is service equipment or a subpanel. Pigtailing neutrals together inside the panel is not a general fix: splices in a panel are permitted in limited circumstances, and combining circuit neutrals defeats the point of separate terminations.
What to inspect on an existing bar
Look for two conductors under one screw. Look for aluminium and copper conductors sharing a terminal, which introduces dissimilar-metal problems on top of everything else. Look for discolouration around any terminal, which indicates it has been running warm. Check that the bar is bonded to the enclosure at the service and isolated from it in a subpanel, which means confirming whether the bonding screw or strap is fitted. And check that each neutral actually belongs to the circuit whose breaker sits nearby, because mixed-up neutrals between circuits are a frequent cause of arc-fault devices tripping after a panel is worked on.
What to check before you act
- Confirm one grounded conductor per terminal throughout the bar.
- Read the panel label for how many grounding conductors a terminal accepts.
- Fit an accessory grounding bar rather than doubling neutrals.
- Verify bonding status of the neutral bar for service versus subpanel use.
Common questions
Can two grounds share a hole on the neutral bar?
Only if the bar listing permits it and the panel documentation says so. The permission is specific to the product, and it never extends to neutrals.
Why does the arc-fault breaker trip after I tidied the panel?
Commonly because a neutral was returned to the wrong circuit. Arc-fault and ground-fault breakers require their own circuit neutral on the breaker pigtail.
The practical takeaway
One neutral per terminal, grounds per the bar listing, and separate bars in a subpanel. When the bar runs out of holes, add terminals rather than conductors, and check that each neutral has gone back to the circuit it came from.
References and further reading
- OSHA: wiring design and protection including grounded conductor requirements
- NFPA: National Electrical Code overview covering panelboards and terminations
- CPSC: home electrical safety checklist including panel conditions
Numerical scenarios are illustrative unless identified otherwise. Follow the exact product instructions; component ratings and local installation requirements can differ.
