Grounding is the part of a van electrical build most people guess at. It is also the part that, done wrong, causes GFCIs to trip, battery monitors to lie to you, and — in a bad case — cables to melt or panels to energize. Here is what actually needs to happen, and why.
Your van chassis is your ground. Bond the DC negative bus to the chassis at exactly one point near the battery. Bond the AC safety ground to the chassis at exactly one point (at the shore inlet or at the inverter — pick one).
Never bond neutral to ground inside the van; that belongs to the shore pedestal or the inverter. Every chassis bond goes to bare metal with a star washer, and the bond conductor is sized for fault current — not signal current.
Safety note: grounding affects shock and fire safety. The principles below follow ABYC E-11 (the closest thing we have to a mobile standard) and NEC Article 551 for the AC side. If you are building something with shore power, an inverter over ~1500W, or anything you are not confident about, have a licensed installer review the work before you energize it.
The word “ground” gets used three different ways in electrical systems, and conflating them is where almost every van grounding question goes off the rails.
Forum posts that say “just ground everything to the chassis” are using the word as shorthand, and sometimes it works — but the shorthand hides the two rules that actually matter:
Once you have those two bonds set up correctly, almost every “weird” grounding symptom — floating voltages, phantom shunt readings, nuisance GFCI trips — goes away. If you want a refresher on voltage, current, and what the chassis is physically doing, the electrical fundamentals page covers it.
The DC bond is a single conductor running from the house-battery negative bus (or negative busbar) to a clean point on the vehicle chassis. It exists for one reason: if a positive conductor shorts to the vehicle frame, the short needs a low-impedance path back to the battery so the main fuse blows immediately.
ABYC E-11 (the marine standard — the closest thing we have to a real “mobile” spec) gives two approaches for the DC grounding conductor:
In practice: if your positive feeder is 4/0 with a 300A class-T fuse, your chassis bond should be 4/0 or 3/0 (one AWG size smaller). Do not use 6 AWG on a 400A system — it will not clear the fault before the insulation melts. For wire-sizing specifics on the positive side, see fundamentals → wire thickness.
If you bond the negative bus to chassis in two places, current can flow through the chassis between those two bond points as a parallel return path. This causes three real problems:
Battery negative goes to chassis at one bond point, all loads return to battery negative through the bus bar, not through the chassis. Click the wires to see gauge sizes.
Educational estimates only — not a substitute for a licensed electrician. Verify against ABYC E-11 and manufacturer specs before installing. See full disclaimer.
BETA — Educational estimate, not an engineered design.
Verify all wire gauges, fuse and breaker ratings, run lengths, and system sizing against ABYC E-11, manufacturer spec sheets, and a licensed electrician before installing or energizing. Ampacity uses ABYC E-11 single-conductor, free-air, 105 °C-insulation copper (typical marine BC-5W2); resistance is NEC Ch. 9 Table 8 at 75 °C; system is nominal 12 V DC and 120 V AC. Wire rated below 105 °C, ambient-temperature derating, and bundle derating are not applied. No code-compliance review or engineering sign-off is provided or implied.
Source: morevanlessmoney.com/tools/electrical/diagram · Full terms: morevanlessmoney.com/legal/terms
If you are using a battery-monitor shunt — a Victron SmartShunt, a Renogy 500A, any of them — the shunt works by measuring every amp of current that passes through it. That means every negative conductor in the system has to be on the system side of the shunt, including the chassis bond.
If the chassis bond is on the battery side of the shunt, any current that returns via the chassis (alternator charging, a DC-DC charger with its own chassis return, an inverter bonded to chassis) will bypass the shunt completely. Your monitor will read a fraction of actual usage.
The failure mode is quiet: the state-of-charge looks reasonable for weeks, then one day the battery is mysteriously empty despite the monitor reading 60%. The shunt was honest about the current it saw; it just never saw most of it.
Your AC system has three wires: hot (black), neutral (white), and safety ground (green or bare). The safety ground normally carries no current. Its only job is to be a low-impedance return path if a hot wire shorts to something metal — like the case of your inverter, or the armor of the shore cable. When that happens, fault current rushes through the green wire back to its source, trips the breaker, and de-energizes the fault before anyone touches it.
In a van, “the source” is either the shore pedestal (when plugged in) or the inverter (when off-grid). Either way, the safety ground ultimately needs to reach the vehicle chassis so that a fault on any exposed metal surface has somewhere to go.
You bond the AC safety ground to the chassis in exactly one place. Two common options:
NEC 551 (the RV article) requires the panelboard-to-chassis bonding conductor to be at least 8 AWG copper. For the green safety-ground wire running inside an AC circuit, NEC Table 250.122 sets the minimum size by the circuit's overcurrent protection: a 30A circuit uses 10 AWG copper minimum, and a 50A circuit is also 10 AWG. Many RV shore cords use symmetric conductors (e.g., a 50A cord built 6/6/6/6) for voltage-drop reasons, but 10 AWG is the code minimum for the EGC.
For the inverter's case-to-chassis bond — the conductor from the inverter's chassis-ground lug to vehicle steel — size it for DC fault current. If the DC positive feeder shorts to the case, the fault clears through this bond, and the fault current is set by the DC main fuse, not the AC breaker. The ABYC 135% rule that sizes the main DC negative bond applies here too. A 3000W 12V inverter on 4/0 AWG with a 300A class-T fuse needs a 2/0 or 3/0 AWG chassis bond, not the 10 AWG the AC side alone would justify. Match or exceed whatever the inverter manual specifies — many premium inverters call for 1/0 or 2/0 directly.
For deeper treatment of shore inlets, transfer switches, and AC wiring, see the shore power guide. For picking an inverter and understanding its ground lug, see inverters.
Neutral-ground (N-G) bonding is the one rule that trips up even experienced builders. The rule:
N-G bonding happens at exactly one point, at the current AC source. Never in the van wiring itself.
If you are wiring an AC panel, the neutral bus must be isolated from the ground bus — they look identical, and they bolt down the same way, but the bonding jumper that comes with the panel has to be removed on a van install. For full treatment of shore vs. inverter power and how transfer switches handle the bond, read shore power.
Classic symptom: the battery monitor reads 20% of actual usage. The builder added a “just in case” chassis bond at the inverter location in addition to the one near the battery. Remove the extra bond; there can be only one.
Often done by accident — the builder left the factory N-G jumper in a breaker panel, or bonded the neutral bus to the enclosure. Plug into a GFCI-protected shore outlet and the GFCI trips instantly, because a portion of the return current now flows back through the ground conductor. Worse: on an unprotected outlet, a hot-to-ground fault in the van can energize the chassis.
Looks fine. Often meters fine through the bolt threads. Does not reliably clear a fault. Paint, powder coat, and underbody coatings are insulators; galvanizing is conductive but builds up surface oxides that raise contact resistance. Grind down to bare steel, use a star washer, then weatherproof the outside of the joint.
These are separate systems. Wiring the green AC ground wire into a DC negative bus defeats the AC safety ground — a hot-to-case fault will energize your 12V system instead of tripping the AC breaker. Always run a dedicated AC safety ground.
A 10 AWG “ground wire” off a 4/0 positive feeder will vaporize before the fuse trips. The bond has to carry peak fault current long enough for the overcurrent device to open. Size to ABYC (same as positive, or one size smaller), not to “what looked about right.”
Every negative conductor — including the chassis bond — has to be on the system side of the shunt. Otherwise the current that returns through the chassis is invisible to your monitor.
Walk through this before energizing. If you cannot check every box, find out why before you close up the van.
One more time, because it is worth repeating: if any part of this is unclear or your install is non-standard (multiple batteries in separate bays, 24V system, dual inverters, mobile-home-style sub-panels), get a licensed RV or marine electrician to review the grounding design before you energize. The cost of an hour of review is trivial compared to a cable fire or an energized chassis.