automatically connect the movable element to the ground buses. These
connections shall make before the main disconnecting devices upon
insertion, and break after the main disconnecting devices upon withdrawal.
Grounding shall conform to[IEEE C37.20.1][IEEE C37.20.2][IEEE C37.20.3]
except that the ground bus shall have a continuous current-carrying
capacity not less than 25 percent of the continuous rating of the power
supply circuit breakers.
2.5.7
Molded Case Circuit Breakers
2.5.7.1
General
Molded case circuit breakers shall conform to the applicable requirements
of NEMA AB 1 and NEMA AB 3, shall be fully rated, and shall have voltage
ratings and interrupting ratings stated. For circuit breakers of the same
ampere frame size, 3 pole and 2 pole circuit breakers shall be the same
width as 3 single pole and 2 single pole circuit breakers respectively.
The circuit breakers shall be manually-operated and shall have trip-free
operating mechanisms of the quick-make, quick-break type. All poles of
each breaker shall be operated simultaneously by means of a common handle,
and shall be enclosed in a common molded plastic case. The contacts of
multi-pole breakers shall open simultaneously when the breaker is tripped
manually or automatically. The operating handles shall clearly indicate
whether the breakers are in "On", "Off", or "Tripped" position. The
circuit breakers shall be of the individually-mounted, stationary type,
shall all be products of the same manufacturer, and shall be
interchangeable when of the same frame size. Each circuit breaker shall be
provided with mechanical pressure type terminal lugs for single-conductor
stranded copper cables of the size required by the specifications or shown.
2.5.7.2
Trip Units
The circuit breakers shall be of the automatic type provided with
combination thermal and instantaneous magnetic trip units. Instantaneous
magnetic trip units shall be set at approximately 10 times the continuous
current ratings of the circuit breakers.
2.5.7.3
480-Volt AC Circuits
Circuit breakers for 480-volt AC circuits shall be rated 600 volts AC, and
shall have a minimum NEMA interrupting capacity of [14,000] [_____]
symmetrical amperes at 600 volts AC.
2.5.7.4
120-Volt and 208-Volt AC Circuits
Circuit breakers for 120-volt and 208-volt AC circuits shall be rated not
less than 250 volts DC, and either 120/240 or 240 volts AC, and shall have
a minimum NEMA interrupting capacity of 10,000 symmetrical amperes.
2.5.7.5
125 Volt DC Circuits
Circuit breakers for 125 volt DC circuits shall be 2-pole rated 125/250 or
250 volts DC, and shall have a minimum NEMA interrupting capacity of 10,000
amperes DC.
SECTION 16404A
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