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How to calculate voltage drop

To calculate the voltage drop in volts the tabulated value of voltage drop (mV/A/m) has to be multiplied by the design current of the circuit Ib, the lenght of run in meters (L) and divided by 1000 ( to convert milivolts to volts).


Voltage drop

Any design must ensure the maximum voltage drop allowed between source and point of use is not exceeded when at full load. Requirements of BS 7671 (17th Edition) limits this to:

  • 3% for lighting (6.9V),
  • 5% drop for other loads (11.5V).


Example :


The voltage drop figure for a given cable is 29mV/A/m. Calculate the voltage drop in a 15m run of this cable when carrying a load of 8A.



For Voltage drop figure see table 4D1A in appendix 6 of the On-Site Guide or Requirements for Electrical Installations: BS 7671:2008.



See also:

 


Recommended :




Megger MFT1720 17th Edition Multifunction Tester MARTINDALE ELECTRIC - SB13 - SOCKET ADAPTOR MEGGER MIT320-EN  FLUKE T5-1000, FOR VOLTAGE AND CURRENT ELECTRICAL TESTING

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