TM 55-4920-328-13 a 30-foot long interconnecting hose assembly, to the test trailer   water   system.      Refer   to   paragraph   14e(2)   for information  on  the  cooling  tower  module.    With  system power  available  from  the  generator  set,  the  following circuit   breakers   in   the   power   distribution   box   on   the auxiliary  trailer  assembly  are  closed  to  make  available 208v ac, 60 Hz, three-phase power to the four motors in the water system: Water Brake Pump CB1 Tower Fan CB2 Tower Fan CB3 Tower Pump CB4 The   INST   PWR   ON   switch   (7,   figure   1-26)   is   then depressed  to  energize  the  No.    2  power  control  panel circuits.        Under    this    condition,    the    BRAKE    PUMP START switch (8), COOLING PUMP START switch (9), TOWER FAN No.  1 switch (10), and TOWER FAN No. 2 switch (11) are then depressed to energize the coils of relays   K1   through   K4   in   the   water   system   circuitry. Energizing   the   relays   applies   electrical   power   to   the respective  motors  in  the  water  system.    The  system  is deenergized in reverse order. (c) Auxiliary trailer power distribution box. The  auxiliary  trailer  power  distribution  box  (2,  figure  1- 32) is located on the aft right side of the auxiliary trailer module  above  the  trailer  deck.    The  power  distribution box is a rectangular sheet metal enclosure approximately  48  inches  high,  20  inches  wide,  and  8 inches  deep.    The  power  distribution  box  is  provided with knock-outs on the side and bottom panels, and has two connectors on the lower front panel.  One connector J1,   identified   CONTROL,   is   used   to   interconnect   the power  distribution  box  with  the  control  circuits  in  the control    cab    module.        The    second    connector    J2, placarded POWER OUT, is used for interconnection of internal   components   with   other   control   and   indicating circuits  in  the  control  cab  module.    Three-phase,  four- wire,  208v  ac,  60  Hz  power  from  the  generator  set  is routed to the power distribution box.  (See figure 7-31.) Connection is made within the unit at four busses: OA, OB,  OC,  and  GRD.    Four  of  the  five  circuit  breakers within  the  unit,  CB1  through  CB4,  are  used  to  connect the primary power source to heavy-duty, motor starters K1  through  K4.    The  fifth  circuit  breaker  CB5  supplies primary   208v   ac   power   to   the   test   trailer   assembly. Motor starters K1 through K4 are identical in design and function  except  for  the  associated  circuitry.    Each  unit consists  of  two  normally-closed  sets  of  contacts,  three normally-open     sets     of     contacts,     thermal     overload protective    elements,    and    a    coil.        These    thermal elements  are  connected  in  series  with  the  three-phase power  circuits  to  the  motors  in  the  water  system.    The normally-closed pair of contacts in series with the relay coil open on an overload to deenergize the relay.  The other  normally  closed  set  of  contacts  open  when  the relay   coil   is   energized   and   close   when   the   coil   is deenergized. When    this    pair    of    contacts    opens    during    system operation,   the   associated   interlock   circuit   causes   a SERVICES  INOPERATIVE  alarm  and  shuts  down  the engine.  Motor starters K1 and K4 are used in the alarm circuits.        The    four    units,    identified    by    reference designation, are used in the following circuits: K1 Water System Water Brake Pump Motor K2 Water System Tower Fan No.  1 Motor K3 Water System Tower Fan No.  2 Motor K4 Water System Tower Pump Motor (2) Cooling  tower  module.    The  cooling  tower module  (figure  1-36)  is  a  centrifugal  fan  blowthrough unit    which    dissipates    heat    from    the    water    being discharged from the water brake assembly. The  cooling  tower  module  operates  as  a  part  of  the auxiliary trailer water system.  The cooling tower module is located behind the water tanks on the auxiliary trailer assembly.  (See figure 131.) The cooling tower module consists  of  a  blower  section  (8,  figure  1-36),  two  7-1/2 horsepower   fan   motors   (5)   and   drives,   and   a   heat transfer     section     (1).          The     blower     section     is     a combination  drain  pan  and  fan  arrangement  consisting of a vee-shaped sump, blow-through centrifugla fans (6) and a heavy supporting angle framework.  Three parallel fans  and  one  motor  are  mounted  on  each  side  of  the sump.  The six fans develop a converging high velocity discharge  column  of  air  which  rises  above  the  cooling tower module before dissipating into the atmosphere. The    air    discharge    pattern    prevents    recirculation    of warm,  moist,  discharge  air  back  to  the  fan  intakes  to prevent  reduction  in  cooling  tower  performance.    The vee-shaped  construction  makes  the  pan  self-cleaning; foreign matter drops to the bottom by the water flowing down  the  pan  sides.    Discharge  cowls  in  the  pan  give the cooling tower module optimum fan performance and air   distribution   through   the   heat   transfer   surface.      In addition,  the  cowls  prevent  falling  water  from  entering the  fans.    Circular  access  doors  provide  easy  entry  to pan interiors.  Removable screens (7) permit access to moving  parts  in  the  fan  assembly.    The  fan  motors, drives,  and  bearings  are  located  under  the  sloping  pan sides for protection from the elements.  A sliding motor mount  permits  easy  vee-belt  tension  adjustment.    The heat transfer section 1-67