Neutral ground continuity after subpanel conversion

Short answer: the continuity you read is supposed to be there. Once an automatic transfer switch takes over as the first point of disconnect, the neutral-to-ground bond moves with the neutral into that switch. Your ohmmeter in the old main panel then reads that remote bond straight through the feeder, and under 1 ohm is a healthy number. The panel itself is right when three things hold: every ground on a bar bolted to the enclosure, every neutral on the insulated bar with the bonding screw out, and the bare rod wire pulled from the panel. The sections below give each reading, the places bonds hide, and the fix.

Why does a converted subpanel still read neutral-to-ground continuity?

The bond is still there, just one panel upstream: a transfer switch that moves the neutral makes the generator side a separately derived system, so the single legal bond sits at the switch and your ohmmeter reads it through the feeder, usually 0.5 ohm or less.

The NEC treats that switch as the start of a new source. A separately derived system gets exactly one bond of its own, and the bond belongs at the switch. Every panel downstream is a subpanel from that moment, with an isolated neutral bar and an enclosure-bonded ground bar.

The meter cannot tell a local bond from a remote one. It reads the whole metal loop: neutral bar, feeder neutral, bond at the switch, ground bar, feeder EGC (the equipment grounding conductor), back to your probes. One reading covers all of it, which is why the number alone decides nothing.

Construction matters as well. On many 200 A load centers both bars start insulated from the can and tied together by a jumper strap behind the main lugs. One screw rarely frees everything on that strap; each connection needs its own removal. The fundamentals sit in subpanel neutral and ground bonding and the grounding and bonding guide.

What should the meter show in a converted panel?

Four readings decide it: under 1 ohm between the bars with the feeder connected, open between them with the feeder neutral lifted, under 0.1 ohm from the ground bar to bare enclosure metal, and open from the neutral bar to bare metal once the neutral is lifted.

Meters and leads differ, so short the leads together and note the offset first. A 0.3 ohm reading on one meter and 0.7 ohm on another can both be healthy. A longer feeder adds loop copper without changing the verdict: at 80 ft [24 m] each way the loop still holds under 0.02 ohm of metal.

What keeps the bars bonded after the bonding screw is out?

Five things turn up, most often first: a bonding screw or strap still seated, a neutral bar still riding its bonding strap, a ground wire landed in the neutral bar, a neutral landed in the ground bar, and a bond somewhere downstream, usually an appliance or a neighboring panel.

1. The bonding screw or strap is still seated. On many panels the screw threads into a strap welded to the neutral bar. Back it out fully and confirm the bar lifts free of it.
2. The neutral bar still rides its mounting strap. Some constructions bond the bar through the strap behind the main lugs even with the screw out. Unbolt the bar from the strap; on a few panels the strap itself has to come off.
3. A ground wire sits in a neutral lug. One 12 AWG ground on the neutral bar bridges the two systems through the branch wiring and the ATS bond. The lifted-neutral test catches it.
4. A neutral sits in a ground lug. The same bridge in reverse, and it also puts neutral current on the ground system.
5. A bond lives downstream. A 3-wire range or dryer cord ties neutral to its chassis by design, and a neighboring subpanel with its bond still in reads the same at your meter.

Both answers you may have heard are right, just for different panels. A factory bonded ground bar needs the bonding screw out and nothing more. A panel with insulated bars only needs a bonded ground bar added.

How do you test isolation without pulling the panel apart?

Lift the feeder neutral and the panel tells the truth: with the power off and the feeder neutral disconnected at the panel, neutral bar to ground bar should read open, while anything under 1 ohm means a bond is still hiding inside this enclosure.

De-energize the panel, lock it off, and verify absence of voltage before any lug comes loose.

1. Short the meter leads together and note the offset.
2. Tag the feeder neutral and lift it from the neutral bar; leave the EGC landed.
3. Meter from the neutral bar to the ground bar. Open is the healthy verdict; write it down.
4. Meter from the neutral bar to a filed bright spot on the enclosure. Expect open here too.
5. Meter from the ground bar to the same spot. Expect under 0.1 ohm.
6. When steps 3 or 4 show continuity, pull branch conductors a handful at a time until the reading opens. The last set you pulled holds the bridge.
7. Reconnect the neutral at the torque marked on the lug, restore power, and read neutral to ground at a loaded receptacle: near 0 V, and under a couple of volts even on a long run.

Worked example: why the connected reading lands near 0.2 ohm. Take a common case: a 200 A load center, 40 ft [12 m] of feeder to the switch in 2/0 copper, and a short bond strap inside the switch.

• Copper: the NEC's dc resistance table lists 2/0 copper at 0.097 ohm per 1000 ft at 75 °C. Copper rises about 0.39 % per °C, so a 20 °C panel room trims it 21 %: 0.097 × (1 - 55 × 0.0039) = 0.076 ohm per 1000 ft.
• Loop: 40 ft of feeder neutral + 40 ft of feeder EGC + about 5 ft of strap and bus = 85 ft.
• Copper in the loop: 85 ÷ 1000 × 0.076 = 0.0065 ohm.
• Terminations: six lugs and the bond strap add roughly 0.1–0.3 ohm in field conditions.
• Meter: 0.1–0.3 ohm with the feeder connected. That is the remote bond talking, and it says nothing about this panel until the neutral is lifted.

What is the fix in the former main panel?

Three moves finish the conversion: land every ground on the bar that bolts to the enclosure, land every neutral on the insulated bar with the bonding screw out and the strap free, and pull the duplicate rod wire so the copper EGC is the only return path.

Give the grounds a bar that bonds to the can. A factory ground bar kit for that panel family bolts into prepared holes and carries its listed bonding connection with it, and the kit's own small screws are part of that listing. An add-on bar takes the bolted treatment: file the paint off the contact surface and clamp with a bolt and nut. NEC 250.12 requires nonconductive coatings such as paint and enamel to come off threads and contact surfaces at grounding connections, unless the fitting is designed to skip that. NEC 250.96(A) says the same thing at system scale: metal parts serving as equipment grounding conductors are bonded together so they can safely conduct any fault current likely to be imposed on them. Bonding the ground bus to the enclosure and ground bar placement on the wall versus the plate cover the hardware.

Keep every neutral on the insulated bar and sweep both bars for misplaced wires. One 12 AWG conductor in the wrong lug undoes the whole afternoon, and the meter test above finds it in seconds.

The 2/0 ground from the transfer switch is a feeder EGC, and the NEC sizes feeder EGCs from the overcurrent device ahead of them in Table 250.122. A 2/0 run on a 200 A switch sits well above that minimum, so the wire size is right and the landing is what matters: bonded bar, stripped contact surface, lug inside its marked range. Removing a neutral-ground bond in an outdoor subpanel walks the same conversion outdoors.

Why remove the ground rod wire from the converted panel?

Because earth is a poor return and the code says so: NEC 250.4(A)(5) rules the earth out as an effective ground-fault current path, and a bare 4 AWG wire left on the subpanel quietly becomes a parallel neutral return the moment any neutral-to-case connection creeps back.

NEC 250.54 gives a driven rod at a remote enclosure a name: auxiliary electrode. It may be connected to the equipment grounding conductor, and it works alongside it, but it never replaces the conductor back to the bond. Earth cannot compete with copper. The worked example above put 0.0065 ohm in an 85 ft copper loop, while a rod-to-earth path reads in the tens of ohms.

The bare wire also builds a parallel road. When any neutral-to-case connection exists downstream, neutral current divides between the feeder neutral and the ground system, and the rod wire is one of the roads it takes. That shows up as stray voltage on the bonded parts near the rod. Pull the conductor at the subpanel end and cap it; the service-side electrode conductor stays. The same arithmetic sits behind parallel neutral current in metal raceway.

How do you keep the separation from drifting back?

Label and record, then the next service cannot undo it: write NEUTRAL, ISOLATED on the insulated bar and GROUND, BONDED on the enclosure bar, keep the readings in the panel file, and land grounds on the bonded bar from the first wire of every new circuit.

• Label both bars at eye level, so the next person with a screwdriver reads before turning.
• File the meter readings with the panel papers: open at the lifted neutral, under 0.1 ohm bar to can, and the date.
• Re-run the lifted-neutral test after any generator or transfer switch service. Bonds creep back at the switch far more often than panels drift on their own.
• Set every new panel up as a subpanel from day one, with grounds on the bonded bar and neutrals isolated.

When does a converted panel need a ground bar kit or a new panel?

Order parts when the panel has no enclosure-bonded bar to take the grounds: the maker's ground bar kit bolts into provided holes and carries a listed bonding connection, and a panel whose neutral bar cannot be separated from its strap is a candidate for replacement, not another phone call.

That last row is our kind of work: custom stainless enclosures are cut to your size and layout in 304 or 316L and delivered in 10 business days from your approval of the drawing.

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