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Unit Removal - TM-5-3895-374-24-1_167
Maintenance After a Fault Has Occurred

TM-5-3895-374-24-1 Paving Machine Bituminous Material: Crawler Mounted Diesel Engine Driven Manual
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TM 5-3895-374-24-1 Insulation Test WARNING  There  is  a  hazard  of  electric  shock  or  burn whenever   working   on   or   around   electrical   equipment Turn off  power  supplying  this  equipment  before  working inside motor control centers. CAUTION  Do  not  megger  solid  state  devices,  capacitor units or any devices which are not designed to withstand megger voltage Disconnect these devices before testing the rest of the motor control center M-37 Before a motor control  center  s  placed  into  service,  (after  installation  or regular  maintenance)  resistance  measurements  should be   taken   Use   an   insulation    tester    (megger)    with    a potential  of  500-1000  volts  Readings  should  be  taken between  each  phase  and  from  each  phase  to  ground both  with  the  branch  disconnects  OFF"  and  "ON  The main   disconnect   should   be   ’OFF"   during   all   rmegger tests. M-37  Megger  readings  with  all  the  disconnects  "OFF" will   typically   be   5-20   megohms   Lower   readings may be observed during start-up on new equipment which has been stored in a damp area If   the   readings   are   above   one   megohm,   a   few branch units may be energized to help dry out the motor   control   center   If   additional   readings   are above    one    megohm,    additional    units    can    be energized    After     the     equipment     has     been     in operation  for  48  hours,  readings  should  be  in  the 5-20 megohm range. When     megger     readings     are     taken     with     the disconnects "ON’ (except for the main) all devices completing   circuits   between   phases   or   between phase and neutral (e.g. control transformers) must be  disconnected  Readings  may  be  slightly  lower, but  the  one  megohm  lower  limit  (during  start-up) should  be  observed.  Record  all  megger  readings below   Any   sudden   change   in   resistance   values (even   if   within   acceptable   range)   may   indicate potential    insulation    failure    Early    detection    and replacement  of  faulty  insulating  components  can help to avoid untimely failure. ‘ If  megger  readings  are  below  5  megohms  (one megohm during start-up) consult your local Square D field office M-38   Return motor control center to service. Energize main first, then each branch unit one at a time. (See Section I-17, Page 12). (Page 3-140)







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