However it is not the only challenge, in addition to the power used by a load to do useful work ( termed real power ) many alternating current devices also use an additional amount of power because they cause the alternating voltage and alternating current to become slightly out-of-sync ( termed reactive power ).
32.
A small-signal AC test current " I x " is applied to the input or output node, all external sources are set to AC zero, and the corresponding alternating voltage " V x " across the test current source determines the impedance seen at that node as " R = V x / I x ".
33.
:: An extract from " BS 6231 : 2006 Electric cables . 600 / 1000 V PVC insulated cables for switchgear and controlgear wiring " here ( BS = British Standard ) says that 600 / 1000 V cables are " intended for use at alternating voltages not exceeding 600 V to earth, and direct voltages not exceeding 1000 V to earth ".
