Voltage Drop: The Silent Electrical Defect That Violates More Than Just “Best Practice”

One of the most frequently overlooked defects in residential construction is voltage drop. Most municipal inspectors and even private home inspectors focus on breaker ratings, conductor size, and device installation, but they rarely ask the critical question of whether the circuit actually delivers the rated voltage to the appliance. This oversight is more than a technical quibble. It is a violation of mandatory code provisions when appliances are forced to operate outside the conditions of their listing and outside the efficiency standards required by the International Energy Conservation Code (IECC).

The 2023 National Electrical Code (NEC), adopted statewide in Texas, references voltage drop in two locations. Section 210.19(A)(1) Informational Note 4 recommends no more than a three percent voltage drop on a branch circuit and no more than five percent total when feeders and branch circuits are combined. Section 215.2(A)(1) Informational Note 2 contains the same recommendation for feeders. While these are “Informational Notes” and not enforceable by themselves, compliance ties directly into NEC 110.3(B), which is mandatory. That section requires that listed or labeled equipment be installed and used in accordance with any instructions included in the listing or labeling. Virtually all appliances, motors, and equipment used in Texas residences are UL listed, and UL standards are tested at nominal voltage plus or minus five percent. Supplying an appliance outside that range violates the UL listing, NEC 110.3(B), and the manufacturer’s installation requirements.

The 2021 International Energy Conservation Code (IECC), which is adopted in Texas, provides additional enforceable provisions that make excessive voltage drop a code violation. Section R403.1.2 requires that equipment be installed in accordance with the manufacturer’s installation instructions. This parallels NEC 110.3(B) and makes the manufacturer’s listed operating voltage range legally binding under the IECC as well. Section R403.7 requires heating and cooling equipment to be sized in accordance with ACCA Manual S and installed in accordance with the manufacturer’s installation instructions. Since efficiency testing such as SEER, EER, and AFUE ratings are performed at nominal voltage, operation below that level prevents the unit from complying with its certified efficiency. Section C405.10, while found in the commercial portion of the code, requires electrical systems to be designed to minimize voltage losses and inefficiency. Although written for commercial systems, the principle underlies the residential requirement that appliances perform at their tested efficiency, and Texas adoption of the IECC recognizes these same principles for energy performance.

When a home’s electrical system is designed or installed with excessive voltage drop, the consequences go beyond dimming lights and nuisance trips. Appliances and HVAC systems operate outside their UL listing, efficiency standards are violated, and warranties are jeopardized. In the defect litigation arena, builders often argue that because NEC voltage drop notes are not “mandatory,” they cannot be held liable. But when cross-referenced with NEC 110.3(B) and IECC Sections R403.1.2 and R403.7, voltage drop becomes a direct code violation. That makes it actionable under the Residential Construction Liability Act (RCLA) and admissible as evidence of substandard construction.

Voltage drop is not just a theoretical concern or a best practice recommendation. It is a defect that violates UL listing requirements, NEC 110.3(B) installation mandates, and IECC Sections R403.1.2 and R403.7. For attorneys litigating construction defect cases in Texas, understanding this often-overlooked issue is critical. It establishes clear grounds to demonstrate that a builder failed to deliver an electrical system capable of operating equipment safely, efficiently, and in accordance with the law.