Quantcast Chapter 7. Electrical Utilization Systems

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7.1 SYSTEM VOLTAGES. The most common utilization voltage in United States industrial
facilities is 480 V. Other voltage levels depend upon motor size, utility voltage available, total
load served, potential expansion requirements, voltage regulation, and cost. The system must be
capable of providing power to all equipment within published voltage limits under all normal
operating conditions.
The preferred utilization voltage for industrial plants is 480Y/277 V. Small dry-type transformers
are utilized to provide 480-208Y/120 V or 480-120/240 V service.
Some loads, particularly large motors above 200 horsepower (hp), can often be served more
economically at voltages above 600 V. When the plant primary voltage is suitable, these large
loads may be served directly at primary voltage. For example, motors over about 200 hp may be
served directly from 2400 V primary systems, motors over 250 hp from 4160 V systems, motors
over 1000 hp from 6900 V systems, and motors over 2000 hp from 13.8 kV systems. Large
motors, or a group of scattered motors, may be served directly from the medium-voltage primary
feeders or through a transformer.
section provides a discussion on the requirements and usage of equipment nameplate ratings and
the effect of deviations in the nominal system voltage from these ratings.
7.2.1 Nameplate Ratings. Utilization equipment is defined as electric equipment which uses
electric power by converting it into some other form of energy. Light, heat, or mechanical
motion are a few examples of converted energy. Each component of the utilization equipment
requires a nameplate. The nameplate must list the nominal supply voltage for which the
equipment is designed. Most utilization equipment (except motors) carries a nameplate rating
which is the same as the voltage system on which it is to be used (e.g., equipment to be used on
120 V systems is rated 120 V; equipment to be used on 208 V systems is rated 208 V, etc.). Single-Phase Motors. Single-phase motors for use on 120 V systems have been
rated 115 V for many years. Single-phase motors for use on 208 V single-phase systems are
rated 200 V, and for 240 V single-phase systems they are rated 230 V. Three-Phase Motors. Prior to the late 1960s, low-voltage three-phase motors were
rated 220 V for use on both 208 and 240 V systems; 440 V for use on 480 V systems; and 550 V
for use on 600 V systems. Nameplate ratings for new motors are 200 V, 230 V, 460 V and 575
V; for use on 208 V, 240 V, 480 V and 600 V systems, respectively.


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