Chapter 12 Branch Circuits and Feeders 151
Copyright Goodheart-Willcox Co., Inc.
Sample Problem 12-6
Problem: A hotel has 250 rooms, each with an area
of 400 ft2. Determine the general lighting load and
then calculate the derated load to be used for feeder
calculations.
Solution: First, determine the total area of the hotel
rooms:
250 rooms × 400 ft2/room = 100,000 ft2
The general lighting load for hotel rooms (from Table
220.12) is 2 VA/ft2. Determine the general lighting
load:
100,000 ft2 × 2 VA/ft2 = 200,000 VA
The branch circuits are required to supply the full
general load. However, the feeder can be derated using
the factors in Table 220.42.
The general lighting load must be divided into three
parts to correspond to the three different demand factors.
The first 20,000 volt-amperes have a demand factor of
50%. The next 80,000 volt-amperes (20,000 to 100,000)
have a demand factor of 40%. The final 100,000 volt-
amperes (100,000 to 200,000) have a demand factor of
30%. Each section is calculated individually:
20,000 VA × 0.50 = 10,000 VA
80,000 VA × 0.40 = 32,000 VA
100,000 VA × 0.30 = 30,000 VA
To determine the derated feeder load, add the three
totals together:
10,000 VA + 32,000 VA + 30,000 VA = 72,000 VA
The derated load used for sizing the feeder is 72,000
volt-amperes.
Receptacle Loads
The majority of receptacles installed in commercial
structures do not supply continuous loads. It is difficult to
predict what size load will be supplied at a receptacle,
unless the receptacle is dedicated (assigned a specific
purpose). The Code does not require a minimum number
of outlets for commercial buildings. Normally, many
receptacles are required.
When a receptacle is the load supplied by an indi-
vidual branch circuit, the receptacle ampere rating must
be equal to or greater than that of the branch circuit.
When there are multiple receptacles on a branch circuit,
the receptacle rating varies with the current rating. See
Figure 12-5, which reflects Table 210.21(B)(3).
Receptacles connected to a 15-amp or 20-amp circuit
are grounded. Grounded receptacles should not be used if
the circuit is not actually grounded. A GFCI receptacle
Table 220.42 Lighting Load Demand Factors
Portion of Lighting Load Demand
to Which Demand Factor Factor
Type of Occupancy Applies (Volt-Amperes) (Percent)
Dwelling units First 3000 or less at 100
From 3001 to 120,000 at 35
Remainder over 120,000 at 25
Hospitals* First 50,000 or less at 40
Remainder over 50,000 at 20
Hotels and motels, First 20,000 or less 50
including apartment From 20,001 to 100,000 40
houses without provision Remainder over 100,000 30
for cooking by tenants*
Warehouses (storage) First 12,500 or less at 100
Remainder over 12,500 at 50
All others Total volt-amperes 100
*The demand factors of this table shall not apply to the computed load of feeders
or services supplying areas in hospitals, hotels, and motels where the entire lighting
is likely to be used at one time, as in operating rooms, ballrooms, or dining rooms.
(Copyright © 2013 NFPA)