2.13.4
Circuit Breakers
All circuit breakers shall be thermal magnetic type.
2.13.4.1
Main Circuit Breaker
Main circuit breaker shall have a maximum capacity of 150 percent of the
electrical load. The main circuit breaker shall be an external handle
mechanism mounted outside the enclosure to permit operation of this breaker
from outside the enclosure. Main circuit breaker shall be provided with
positive locking device to permit locking the operating handle.
2.13.4.2
Branch Circuit Breakers
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NOTE: Delete reference to comminutor when not
required for plant. For plants of 1.09 L/s 25,000
GPD capacity and below, the comminutor and bar
screen unit may be omitted, and in lieu thereof, a
screening basket provided in the aeration tank. For
installations in which all sewage has passed through
a comminutor and bar screen upstream of the plant, a
comminutor and bar screen unit need not be provided
as a part of the plant equipment.
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NOTE: Delete reference to mechanical aerator when
step aeration type or complete mixing type is
specified, or when not allowed for extended aeration
type. Mechanical aerator may not be suitable for
use in areas having prolonged periods of
sub-freezing temperatures when spray may form
accumulation of ice. Consideration should be given
to temperature and detention time of the liquid and
freeboard in the tank in determining temperatures
that may be tolerated. Mechanical aerator is not
suitable for extended aeration type where eventual
conversion to step aeration is contemplated.
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NOTE: Delete reference to sludge collector drive
motor for extended aeration type below 6.60 L/s
150,000 GPD capacity. For plants below 0.66 L/s
15,000 GPD capacity, hopper bottom only should be
specified for settling tanks. For plants above 4.38
L/s 100,000 GPD capacity, mechanical sludge
collectors only should be used in settling tanks.
For plants between 0.66 L/s and 4.38 L/s 15,000 and
100,000 GPD capacity, either hopper bottom or
mechanical sludge collector should be allowed as a
Contractor's option. However, of the various types
of mechanical sludge collectors, rotating sludge
collectors appear to be available for plants of 1.31
L/s 30,000 GPD and above; chain-and-flight, 1.75 L/s
40,000 GPD and above; traveling reciprocating type,
0.66 L/s 15,000 GPD and above.
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SECTION 11375N
Page 72
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