Electric Motor Control Basics - Book - Page 10
Industrial Control Basics: Part 1, Contactors
NEMA vs IEC
There are two standards for contactors: NEMA and IEC.
NEMA (National Electrical Manufacturers Association) is the largest trade association
of electrical equipment manufacturers in the United States. NEMA encouraged
manufacturers to standardize on frame sizes to allow users to confidently specify,
purchase, and install electrical components from different manufacturers without a lot
of hassle and cross-referencing. NEMA contactors also are designed with safety factors
that go beyond design ratings (oversized), up to as much as 25%. NEMA is primarily a
North American Standard.
NEMA contactors for low-voltage motors (less than 1,000 volts) are rated according
to NEMA size, which gives a maximum continuous current rating and a rating by
horsepower for attached induction motors. NEMA standard contactor sizes are
designated 00, 0, 1, 2, 3 to 9.
IEC (International Electrotechnical Commission) is a global standard. IEC contactors
are not oversized. They are smaller than NEMA contactors and less expensive. The
range of sizes offered by manufacturers is more numerous than the ten NEMA
standards. As such, they are more specific to a given application and are specified when
the operating conditions are well understood. Whereas, NEMA may be chosen when
operating conditions, such as load are not well defined.
IEC contactors are also “finger safe.” Whereas NEMA requires safety covers on
contactor terminals. Another key difference is IEC contactors react faster to overloads,
NEMA contactors are better at withstanding short circuits.
Part 1, Contactors
Basics: Part 2,
Basics: Part 3,
The Benefits of Type E/F
Basic Pump Control:
Three Phase DOL Starter
Control of an Electric Pump
Applying Motor Control
in a Wastewater
NEMA vs IEC Motor