154 Modern Commercial Wiring
Copyright Goodheart-Willcox Co., Inc.
Figure 12-6. The load for multiple pieces of commercial cooking
equipment can be derated in accordance with the demand
factors listed in Table 220.56.
Units of Equipment Demand Factors (%)
1–2 100
3 90
4 80
5 70
6+ 65
Feeder Demand Factors for
Kitchen Equipment
NEC NOTE 220.56
Demand factors for kitchen equipment shall be
applied to all equipment that has either thermostatic
control or intermittent use as kitchen equipment. They
shall not apply to space-heating, ventilating, or air-
conditioning equipment.
Heating and Cooling Loads
Regardless of the type of structure—residential,
commercial, or industrial—the heating load must be
computed at 100% of the nameplate rating of the unit.
Depending on the type of heating unit, the branch circuit
may require other considerations.
Fixed electric space heating is covered in detail in
Article 424—Fixed Electric Space-Heating Equipment.
This article includes fixed equipment, such as central
heating systems, boilers, heating cable, and unit heaters
(baseboard, panel, and duct heaters). For information
regarding the installation, control, and specifics about
each type of heater, refer to Article 424.
The Code also requires a disconnect for the heater
and motor controller, as well as supplementary overcur-
rent protection for any fixed electric space-heating units.
The disconnect is for safety during maintenance. The
disconnecting means must be within sight of the unit and
must disconnect all components of the heating unit,
including any overcurrent protective devices, contactors,
elements, and motor controllers.
The rules for sizing the branch-circuit wiring and
overcurrent protection are very specific. The rating on the
equipment nameplate is used to determine the load. If the
equipment operates continuously for at least three hours,
its rating must be increased by a factor of 1.25.
Fixed electric space heating shall be considered
continuous load. Several general rules must be followed
when sizing the overcurrent protective devices for branch
circuits supplying heating equipment (see Section
424.22):
• Heating equipment is protected by the branch-
circuit overcurrent protective device. This can be
a set of fuses or circuit breakers.
• Motors used in conjunction with the heating
equipment must also have overcurrent protection.
• Heating units having resistance elements exceeding
48 amps must have their load subdivided. Each of
the loads must have overcurrent protection provided
by the manufacturer. Conductors from the overcur-
rent devices to the heating unit must be sized at
125% if the load is 50 kilowatts or less.
• If the unit load for the heating equipment is greater
than 50 kilowatts, the conductors can be sized at
100% provided the heating unit has a controller
(thermostat). If this is not the case, then the
conductors must be sized at 125% of the load.
• For conditions other than those described above,
size the conductors at 125% of the load.
Sample Problem 12-10
Problem: A 30-kilowatt, 240-volt heating unit with
a 6-amp fan motor is being installed for a shoe store.
Determine the size of the THW conductors and over-
current protective device for the circuit supplying
the equipment.
Solution: First, determine the current required for
the heating unit:
I =
P
E
=
=
30,000 VA
125 A
240 V
Combining the current for the heating unit and the
motor:
Required current = 125 A + 6 A
= 131 A
The conductors must be designed for 125% of this
current (Section 424.3(B)):
Required conductor capacity = 131 A × 1.25
= 164 A
The overcurrent protective device must be the next
highest standard size (Section 240.6), which is 175 amps.
Using Table 310.15(B)(16), 2/0 AWG copper conduc-
tors are needed. The equipment grounding conductor
can be a 6 AWG copper conductor (Section 250.122).