An essential part in the life of an electrician is performing
load calculations. Determining what size conductors and
overcurrent protective devices to install is something most
electricians do on a daily basis. Specifications for calculating
branch-circuit, feeder and service loads are in Article 220 of
the National Electrical Code (NEC). This article is divided into
five parts. Part I covered general requirements for calculation
methods (Electrical Contractor, March 2006). Branch-circuit load
calculation methods are covered in Part II. Calculation methods
for feeders and services are covered in Parts III and IV. Part V
provides calculation methods for farms. This month’s column is
the second part in a series dedicated to clarifying the load
calculation requirements stipulated in Article 220. Sections
220.3 and 220.5 are included in the general specifications in
Article 220. New to the 2005 edition of the NEC is 220.3 and
Table 220.3. Other articles contain load-calculation
requirements in specialized appli-