Inspector fails a water heater circuit because the wires inside the Romex weren't size-stamped

On size, the circuit holds up. NEC 422.13 treats storage water heaters as continuous loads sized at 125 percent of their rating, home inspector Reuben Saltzman of Structure Tech explains. A 3,500-watt heater at 240 volts draws about 14.6 amps, so the minimum is about 18.2 amps, and a 25-amp breaker on 10 AWG copper clears it. The dispute was about markings.

NEC 310.8 requires conductors and cables to carry the voltage rating, type letters, maker and AWG size, as Christel Hunter, vice president of standards at Cerro Wire, laid out in IAEI Magazine. On NM cable, that print is on the jacket. The insulated wires inside are different. UL 719, the NM product standard, allows THHN-type insulation but bars printing THHN, -B or any temperature rating on those conductors, according to a moderator on Mike Holt's forum who cited the standard. Southwire's Romex literature says the inner conductors are not listed or marked as any NEC wire type and may not be installed apart from the complete cable. Conductors running without the jacket inside panelboards and boxes to their terminals still count as part of the cable.

So the call turns on where the jacket came off. Cable stripped only inside the heater's junction box is still NM. Inner conductors pulled loose through conduit or run on their own are unmarked single wires, and the inspector has code text behind a fail. Electricians on Mike Holt's forum have argued for years that the inners should simply be marked THHN, which would end this fight.

When a call looks wrong, ask for the code section and bring the listing or the manufacturer's spec sheet before tearing anything out. Appeal routes are set locally. In Wake County, N.C., contractors go first to the chief electrical inspector, who can also adjust reinspection fees, then to a three-member appeals committee (the form is due within 10 working days of the inspection), and then to the state Department of Insurance.