Nonmetallic-sheathed cable (NMC) (fig. 9-14, view  A)  is  more  commonly  called  by  the  trade name   “ROMEX,”   ROMEX  (NMC)  comes  in sizes No. 14 through 2 for copper conductors and No.  12  through  2  for  aluminum  or  copper-clad aluminum  conductors.  This  type  of  cable  comes with a bare (uninsulated) ground wire. The ground wire is laid in the interstices (intervals) between the circuit conductors and under the outside braid. The ground wire is used to ensure the grounding of  all  metal  boxes  in  the  circuit,  and  also  to furnish   the   ground   for   the   grounded   type   of convenience  outlets  that  are  required  in  Navy installations. Nonmetallic-sheathed cable is used for temporary wiring in locations where the use of conduit would be unfeasible. The use of Romex as service entrance cable, in garages, in storage battery  rooms,  imbedded  in  poured  concrete,  or in  any  hazardous  area  is  NOT  authorized. Metallic-armored  cable  (fig.  9-14,  view  B),  also called BX cable, is used in naval installations for temporary  wiring,  but  unlike  Romex,  its  use  in commercial  installation  is  restricted.  Most  city building codes restrict the use of BX cables to oil burner  control  circuits  and  the  like.  A  difficulty with BX is the fact that it tends to ground after installation.  Small  metal  burrs  on,  the  armor  can, because  of  vibration,  penetrate  the  insulation  and cause  a  ground. BX  cables  come  in  sizes  from  No.  14  to  2 AWG,  and  each  cable  may  contain  one,  two, three, or four conductors. The armor on the cable furnishes  a  continuous  ground  between  boxes. Insulation As  mentioned  earlier,  electrical  conductors  are available  with  various  kinds  of  insulating materials.  Some  of  these  are  rubber,  thermo- plastic,  and  varnished  cambric.  Special  types  of paper,  glass,  silk,  and  enamel  are  also  used  to insulate conductors, but with less frequency than those  previously  mentioned.  The  NEC^® recom- mends  insulation  of  certain  kinds  for  use  in dry,  damp,  and  wet  locations.  Underground installations, those in concrete slabs and masonry, those in direct contact with the earth, and those subject to saturation with water or other liquids are  considered  wet-location  installations. Another  factor  to  consider  in  the  choice  of insulation  is  temperature.  Different  insulations have  different  maximum  temperature  ratings. Check   the   NEC^® and   applicable   LOCAL CODES to be sure you are using the appropriate insulation  for  the  location  and  temperature considered  in  the  plans.  Some  examples  of  the composition   of   insulation,   the   location   that applies, and their maximum temperature rating follow: Type  RH  is  a  heat-resistant  compound,  that will stand higher temperature than Type R. This type  is  commonly  used  in  dry  locations.  The maximum  temperature  rating  is  167°F. Type   RHW   is   a   moisture-resistant   rubber compound for use where the wire may be subject to wet conditions. This type is used in both wet and  dry  locations.  The  maximum  temperature rating  is  167°F. Type RUH is a high grade rubber compound, consisting of 90-percent latex. This type is often used  for  direct  burial  in  dry  locations.  The maximum  temperature  rating  is  140°F. Thermoplastic  insulation  has  the  advantage  of long life, toughness, and a dielectric strength (that is,  a  capacity  for  insulating)  equal  to  that  of rubber.  It  requires  no  protective  covering  over  the insulation.   Common   types   of   thermoplastic insulation  are  Types  T,  TW,  and  TA.  Type  T  is suitable  only  for  dry  locations  with  a  maximum temperature   rating   of   140°F.   Type   TW   is moisture-resistant,  and  again,  with  a  temperature rating  of  140°F.  Type  TA  is  a  thermoplastic- asbestos compound that combines the character- istics  of  Types  T  and  TW.  This  type  has  a maximum temperature rating of 194°F. Its use is restricted  to  switchboard  wiring. Varnished cambric insulation has an insulating quality midway between that of rubber and paper. It  is  more  flexible  than  paper;  its  dielectric  strength is  greater  than  that  of  rubber.  This  type  is  not adversely affected by ordinary oil and grease. It is  manufactured  in  either  standard  type  (black finish),  or  in  the  heat-resistant  type  with  a  yellow finish.  Varnished  insulation  is  restricted  to  dry locations   in   areas   such   as   motor   leads, transformer  leads,  and  high-voltage  cables. Conduits and Fittings An electrical conduit is a pipe, tube, or other means in which electrical wires are installed for protection  from  accidental  damage  or  from  the elements. If pipes or tubing is used, the fittings depend  upon  the  pipe  or  tubing  material.  The 9-10