(Originally published in the April 2006 Housing Journal)

Electrical Bureau Addresses Voltage Drop Clarifications

Attached is a copy of the code interpretation of the voltage drop requirement, supplied by Electrical Bureau Chief Rem Pacheco. The Electrical Bureau and TAC are currently looking at amending the 2005 NMEC Section 210.19 A that would incorporate the attached clarifications into the code.

CODE SECTION: 2005 New Mexico Electrical Code 210.19 (A) General. Voltage Drop.

Following is the interpretation of the Electrical Bureau with Electrical Technical Advisory Council (TAC) recommendation of 2005 NMEC Section 210.1(A):

  • Conductor length limitations of 75 feet and 150 feet shall apply to General Purpose Branch Circuits, 120 volts nominal between conductors.
  • General Purpose Branch Circuits that exceed 150 feet, General Purpose Branch Circuits that contain mixed conductor sizes, Individual Branch Circuits, Appliance Branch Circuits and branch circuits over 120 volts, nominal between conductors shall be sized so that the total circuit voltage drop does not exceed 5%.
  • It shall be permissible to install mixed conductor sizes in a branch circuit to compensate for voltage drop provided the total voltage drop of the branch circuit does not exceed 5% and the overcurrent protection device rating does not exceed the ampacity rating of the smallest conductor in the circuit.
  • The ampacity to be used when calculating voltage drop shall be permitted to be 80% of the General Purpose Branch Circuit overcurrent protection device rating, or the connected load of an Individual or Appliance Branch Circuit.
  • Smoke detector circuits in a single-family dwelling are exempt from the conductor length limitations since the load is minimal.
  • Lighting switch leg and switch traveler conductors are exempt from the conductor length limitations provided the voltage drop of the branch circuit does not exceed 5%.
  • The conductor resistance values of 2005 NEC Chapter 9 Table 8 may be used when calculating voltage drop and the basic voltage drop formula found in the 2005 NEC Handbook page 98 may be used.

Pacheco also stated that an electrical panel is permitted to be installed in any room of a dwelling including hallways, except clothes closets, bathrooms, cupboards, pantries or similar locations that restrict ready access (2005 NEC 240.24, 2005 NMEC 240.24 F). A panel must maintain a minimum of 3 feet working space in front of the panel and must be readily accessible for operation (2005 NEC 110.26, 240.24 A). This means an electrical panel may not be installed behind a picture or other obstruction that would make it not readily accessible.