Water heater junction box
What's wrong here?
- The white conductor is used as a hot without being re-identified
- A 240 V water heater circuit must include a neutral conductor
- 10 AWG copper is too small for a 4500 W water heater
- Nothing. This installation is compliant
Show the answer and the code reference
The answer
The white conductor of the 10/2 cable is being used as an ungrounded conductor (spliced to the red whip conductor) with no tape or other re-identification.
Correct choice: 1. The white conductor is used as a hot without being re-identified
In a 240 V circuit made with 2-wire cable, both insulated conductors are hot, so the white is carrying 120 V to ground. 200.7(C)(1) allows the white conductor in a cable assembly to be used as an ungrounded conductor only if it is permanently re-identified by tape, paint, or other effective means at its termination and wherever it is visible and accessible, with a color other than white, gray, or green. Without it, the next person in the box reasonably assumes the white is a grounded conductor and treats it as dead.
How to fix it
Wrap the white conductor with black or red tape around the full circumference near each end, in this box and at the breaker in the panel, so it is plainly marked as ungrounded.
Code references
NEC 2023 200.7(C)(1) — Use of Insulation of a White or Gray Color or with Three Continuous White or Gray Stripes — Circuits of 50 Volts or More
A white or gray conductor in a cable assembly may be used as an ungrounded conductor only if it is permanently re-identified by marking tape, painting, or other effective means at its termination and at each location where it is visible and accessible. The re-identification must encircle the insulation and be a color other than white, gray, or green.
Drills citing 200.7(C)(1)NEC 2023 422.13 — Storage-Type Water Heaters
A fixed storage-type water heater with a capacity of 450 L (120 gal) or less is considered a continuous load for sizing branch circuits, so the branch circuit is sized at not less than 125 percent of the nameplate rating.
Drills citing 422.13
2026 NEC:not yet checked Confidence: low
Minnesota
Minnesota adopted the 2023 NEC without amendment as the Minnesota Electrical Code (Minn. Rules 1315.0200; Minn. Stat. 326B.35), effective July 1, 2023, so 200.7 and 422.13 apply as published. That edition governs permits filed through Aug. 16, 2026; permits filed on or after Aug. 17, 2026 fall under the 2026 NEC; see the 2026 NEC note on this drill for how the cited section fares there.
How Minnesota adopts the NECWhy the other choices are wrong
- A 240 V water heater circuit must include a neutral conductor. A straight 240 V load has no neutral connection. A 2-conductor cable with ground is correct for this heater.
- 10 AWG copper is too small for a 4500 W water heater. 4500 W at 240 V is about 18.8 A; at 125 percent (422.13) that is about 23.4 A, well within 10 AWG copper on a 30 A breaker (240.4(D)(7)).
- Nothing. This installation is compliant. Using the white of a cable as a hot is allowed only when it is permanently re-identified at every termination and every place it is visible and accessible (200.7(C)(1)). This white is bare of any marking.