TM  5-6115-323-14 ating   times.   Consider   installation   of   the   tanks underground if the installation will be longer than temporary.  Locate  the  tanks  as  near  the  shelter as  practicable  and  be  certain  that  the  bottoms  of the  tanks  are  not  lower  than  four  feet  (120  centi- meter) from the fuel pump on the installed gener- ator  set.  Connect  the  fuel  line  from  the  external source  to  the  auxiliary  fuel  valve. (5) Support.  Be  certain  that  the  bearing  sur- face  used  can  support  the  weight  of  the  generator set. (6) Foundation.  Since the unit is of the porta- ble   type,   no   foundation   should   normally   be   re- quired.  However,  position  the  unit  on  reasonably firm, dry ground using planks, timbers, or a suita- ble  gravel  base,  as  available  conditions  warrant. Provide  for  water  drainage  away  from  the  unit. (7)  Mounting.  Position  the  unit  so  that  it  is situated  in  a  level  plane  and  so  that  the  frame  is supported  on  its  entire  bottom  surface.  If  neces- sary, the frame may be secured to a suitable base. c. Grounding   Procedure. WARNING Do   not   rely   on   grounding   or   safety devices   to   prevent   accidents.   Electrical circuits   and   equipment   are   potentially hazardous.   Personnel   should   always   ex- ercise  caution  to  prevent  injury  or  pos- sible  death  due  to  electrical  shock. Generator   sets   shall   be   grounded   in order  to  prevent  shock  due  to  defective insulation,   or   external   electrical   faults. Poor   grounding   can   endanger   person- nel,   may   damage   equipment,   and   can create  interference  in  communication  or electronic   circuits. (1)   Install   one   of   the   following   items   as   a grounding  device: (a) Drive a ground rod to 8 feet. (b)  Drive  a  ground  pipe, steel,  to  a  depth  of  at  least  8 underground  pipe  may  be  used a depth of at least 3/4  inch  copper  or feet.   An   existing in  an  emergency. (c) Bury a  1/4 inch  thick  iron  or  steel  plate, approximately  18  inch  x 18  inch  size,  with  ground cable attached, to a depth of at least 4 feet. (d) Bury a ¹/16  inch  thick  aluminum  or  cop- per  plate  approximately  18  inch     x 18  inch  size, with  ground  cable  attached,  to  a  depth  of  at  least 4 feet. (e)  Position  a   1/4  inch  thick  iron  or  steel 4-2 plate, or 1/16 inch thick aluminum or copper plates, approximately  18  inch  x 18 inch size, on the hard ground  or  bedrock  beneath  the  trailer  stand  or roll the wheel of a trailer or truck until it comes to rest on top of the grounding plate. (f) Saturate  the  area  around  the  grounding device  with  water  to  increase  conductivity. (2)  Ground  cables  should  be  copper.  Braided cable is the best, but No. 6 AWG gauge (or larger) copper wire will suffice. (3)   Connect   the   ground   cable   from   the grounding  device  to  the  generator  set  frame ground stud (figs. 1–1 and 1-3) and tighten the nut securely. d.  Electrical  Connections.  All  internal  electrical connections  for  proper  operation  of  the  generator sets  have  been  made  by  the  manufacturer.  If  it appears  that  changes  have  been  made  in  the wiring,  refer  the  matter  to  Direct  Support  (Inter- mediate)  maintenance. (1)  Power  transmission  cables  (model  MEP- 015A)   (AC  unit).   Use  cable  with  a  minimum  wire size  of  No.  12  AWG.  This  size  will  give  a  voltage drop of about 1 volt per 25 ft. (750 centimeters) of cable when the unit is operated at full load. If the distance to the load is great, increase the wire size to No. 10 or No. 8 to minimize voltage drop. (2)  Power  transmission  cables  (model  MEP- 025A)  (DC  unit).   When  the  DC  unit  is  used  for battery  charging,  the  battery  cables  will  normally be  both  adequately  sized  and  short.  However, other  installations  may  at  some  time  be  made. Use,  as  a  minimum  size,  cable  of  No.  4  AWG  for distances up to 25 ft. (750 centimeters). For longer distances, No. 3, No. 2, or No. 1 AWG sizes should be used. (3)  Power   output   connections.   Turn  the  load switch  (AC  Unit)  or  circuit  breaker  (DC  Unit)  to the OFF position and connect the power transmis- sion  cables  at  the  load  terminals.  Refer  to  figure 2-3. CAUTION When   connecting   the   power   cables   on the   DC   unit,   observe   the   polarity   mark- ings   on   both   the   load   and   the   generator set   and   make   the   connections   in   the correct  relationship  (+  to  +  and  –  to  –). When   connecting   the   AC   Unit,   the   ter- minal   relationship   (LI   and   L2)   to   the equipment   may   be   important   to   some equipment   with   which   the   unit   may   be used.   When   the   relationship   is   impor- tant,  match  the  terminals  to  the  load  (Ll