What 393.28 means in plain language
When an inspector writes you up under 393.28, they've determined that electrical wiring somewhere on your commercial motor vehicle is installed incorrectly, isn't properly secured, or lacks adequate protection from heat, abrasion, or other damage. The rule covers the entire wiring system — from the cab back through the chassis and into any trailer connections your tractor is pulling.
The practical concern behind this regulation is fire and electrical failure. Wiring that isn't routed, secured, or protected correctly can chafe against metal edges, overheat, or arc — creating the conditions for a short circuit or a cab fire. Inspectors are looking for bare conductors, unsupported wire runs, missing grommets where wires pass through metal panels, and connections that aren't adequately insulated or protected.
This is a relatively subjective call compared to something like a cracked brake drum. The inspector is exercising judgment about whether the installation meets a reasonable standard of protection. That means documentation of recent electrical repairs and a tight pre-trip inspection of visible wiring can matter a great deal if you contest the citation.
What our enforcement data actually shows
Here's the first piece of information most drivers want: 393.28 is not OOS-eligible under normal circumstances, and our inspection records back that up. Across all 6,422 all-time citations in our database, only 102 resulted in a vehicle being placed out of service — a 1.6% OOS rate. To put that in context, the all-FMCSR average OOS rate across every code we track is 31.4%. This code comes in dramatically below that average, meaning in the overwhelming majority of cases — 6,320 out of 6,422 — the driver kept rolling after the citation was written.
That said, it isn't zero. In the last 12 months, our database recorded 1,480 citations for 393.28, and in just the last 90 days, 347 citations were issued. Those are active, current enforcement numbers, not historical artifacts. Looking at the monthly trend, citations have been running between 103 and 163 per month for most of the past year, with January 2026 (157 citations) and February 2026 (163 citations) representing the highest recent months. The volume tells you that inspectors across the country are actively writing this code — it ranks #300 out of 3,036 FMCSR codes by all-time citation volume, which puts it solidly in the upper tier of commonly cited violations.
The CSA severity weight is 3, which is on the lower end of the severity scale. The citation will still land on your CSA record and contribute to your carrier's Vehicle Maintenance BASIC score, so don't dismiss it — but it's not a 10-point violation.
Who gets cited most
Looking at the last 180 days of our inspection records, Texas dominates the citation count by a wide margin, with 739 citations — far ahead of any other state. Illinois comes in second with 21 citations, and Iowa third with 6 citations. The OOS-rate variation across those top states is worth noting: Texas sits at just 0.3% OOS, while Illinois comes in at 19.0% and Iowa at 16.7%. That's a spread of more than 16 percentage points, which is material. If you're running through Illinois or Iowa and get flagged for a wiring issue, the data suggests inspectors in those states are more likely to make an OOS determination, even though the national rate is low.
On the carrier side, our data shows fleets such as RUBEN CARLOS TREVINO SANCHEZ (USDOT 1649689) with 65 all-time citations and RS TRANSFER SA DE CV (USDOT 1156825) with 35 all-time citations appearing at the top of the citation counts. The concentration of citations at specific DOT numbers underscores that wiring issues tend to be systemic — a fleet-wide maintenance culture problem rather than a one-off bad day.
Freightliner trucks (FRHT) account for 1,123 of all-time citations under this code, with Kenworth (KW) at 619 and Peterbilt (PTRB) at 415. Given that Freightliners make up a large share of the total fleet population, the raw numbers aren't surprising — but they do signal that drivers operating any of these platforms should be especially diligent.
How severe is this compared to similar codes
Within the Vehicle Maintenance category, 393.28 is a relatively minor enforcement event by both volume and OOS impact. Compare it to 393.9(a) — Inoperable required lamps, which carries 660,737 all-time citations and a 15.4% OOS rate. That's more than 100 times the citation volume of 393.28, and a dramatically higher OOS risk. Similarly, 396.3(a)(1) — Inspection/repair/maintenance general sits at 236,919 citations and a 45.3% OOS rate — a code where nearly half of all citations result in a vehicle being parked.
Closer to home, 393.11 — Lighting devices/reflectors has 179,734 citations and a 1.8% OOS rate, which is the most comparable peer code in terms of OOS exposure. The pattern across these comparisons is consistent: 393.28 is a real violation that goes on your record and costs CSA points, but it doesn't carry the immediate operational shutdown risk that general maintenance and brake-related codes do.
How to avoid it
The co-occurring violation pattern in our 90-day data is a roadmap for where to look during your pre-trip. These codes appeared on the same inspections as 393.28 most frequently:
- Check every exterior lamp before you move. 393.9 (Inoperable Required Lamp) appeared in 160 shared inspections with 393.28 in the last 90 days. A burned lamp is almost always a wiring symptom — don't just swap the bulb and move on. Look at the connector and socket for corrosion or bare wire.
- Walk the brake air lines. 393.45B2UV (Brake tubing/hoses inadequate) showed up in 94 shared inspections. While that code addresses the tubing itself, inspectors who find damaged air lines are also scanning adjacent wiring harnesses. Inspect both together on your pre-trip.
- Look for fuel system issues. 396.5B (Fuel system leak) co-occurred in 85 shared inspections. Fuel and exposed wiring in the same area is an obvious fire hazard — if you spot a fuel odor or wet spot near a wiring bundle, flag it immediately.
- Inspect wiring visible in the engine compartment and frame rails. Pay attention to any wire that runs near an exhaust component. 393.83G (Exhaust discharge) appeared in 56 shared inspections, and exhaust heat is one of the most common causes of insulation breakdown.
- Confirm your periodic inspection documentation is on the truck. 396.17C (No proof of periodic inspection) co-occurred in 53 shared inspections. If you also can't produce inspection records, a minor wiring citation turns into a paperwork violation stack.
- On Freightliner, Kenworth, and Peterbilt equipment specifically, be aware that the high citation volumes for these makes mean inspectors are familiar with common wiring failure points on each platform — connectors at the back of the cab, trailer harness pigtails, and chassis ground straps are worth a deliberate look every pre-trip.