2. If you do not find the trouble, or open, by a visual check, use a voltmeter to determine whether the circuit  is  live  (operating)  up  to  the  point  of  the component. A  SHORT  CIRCUIT  results  when  two  bare conductors  of  different  potential  come  into  contact  with each other. If a conductor inadvertently contacts a metallic part of a wiring system, such as a motor frame or  conduit,  the  system  is  sometimes  said  to  be GROUNDED  instead  of  having  a  short  circuit. Grounds or short circuits can be (1) solid, (2) partial, or (3)  floating.  This  situation  presents  a  serious  safety hazard  because  the  machinery  may  be  in  operation, even  though  it  has  a  short  circuit.  This  condition  is especially true in motors and some appliances. A solid ground or short circuit is one in which a full- voltage reading is obtained across the terminals of a blown fuse when the load is disconnected from the circuit. The circuit resistance, in this case, is quite low, and the current is quite high so that the fuse will blow. A partial short or ground is one in which the resistance between the phase wires, or between the phase  wire  and  the  ground,  is  partially  lowered. However, enough current still remains to blow the fuse. Grounds of this type are generally more difficult to locate than are solid grounds. A floating ground is a condition in which the resistance of the defect in a system varies from time to time.  Grounds  of  this  type  may  be  present  in  an electrical system for some time before their existence becomes known. A floating ground is indicated when fuses are blown on the phase side of a circuit a number of times, and a circuit test shows no defects in the system. In grounds of this type, fuse trouble may not occur for several days. Then the ground recurs, and the fuses are blown again. The   procedures   used   to   repair   the   troubles mentioned thus far are usually fairly simple. In the case of an open, short, or ground in NM cable, the bad section from box to box can simply be replaced using the same procedures outlined for installation. Another method would be to cut the cable at the trouble spot, install junction boxes, and add a short piece of cable to replace the bad section. Although the latter is the cheapest, it may  not  be  possible  if  the  trouble  is  concealed. Remember, you must have at least 6 inches of free conductor in a junction box to make the splices. Once you find out where the trouble is in a conduit system, the repair procedure is even easier. All that is required is to pull the open, shorted, or grounded conductor out and replace it with a new one. This replacement  can  be  done  by  attaching  the  new conductor to the one that is to be removed. In any case, a little common sense and knowledge of the NEC© requirements will dictate the action you should take. METERS Many times a visual inspection does not uncover an apparent problem; therefore, you must advance to troubleshooting   with   meters.   In   electrical troubleshooting, you will use voltmeters, ohmmeters, ammeters,  and  the  meter  that  incorporates  many meters—the multimeter. When using a voltmeter, you have to connect the power to the circuit before testing. On the other hand, you cannot use the ohmmeter on an energized circuit. You need to start voltmeter tests at the power input end of the circuit, whereas you start ohmmeter tests at the ground  end Electrical circuit troubles develop either in the wiring or in the operating unit. If you analyze the problem carefully and take systematic steps to locate it, not only will you save much time and energy, but you will also prevent damage to expensive equipment. Either dead circuits or live circuits can be tested with  instruments.  Circuit  defects  can  sometimes  be located more easily by one method than the other, depending upon the type of circuit and the trouble. To test a dead circuit, disconnect the device from the outlet or disconnect switch. Equipment for this method of testing includes such units as ohmmeters and battery-powered test lamps. Asuitable continuity tester can be made easily from a flashlight in an emergency. An ohmmeter that contains its own batteries is excellent for continuity testing. A basic factor to consider in choosing continuity test equipment is to use relatively low-voltage  instruments,  reducing  the  danger  of sparking. WARNING When  connections  are  made  in  the presence of combustible vapors, sparking is a serious fire hazard. When  you  test  live  circuits,  energize  the  circuit under test from the power source. Generally, you will test with a voltmeter. Make certain that the voltmeter is designed for the type of current to be tested and has a 5-38