VOLTAGE DROP CALCULATIONSMARCH 12, 2014 MOHAMED A. MOUSSA 2 COMMENTS

Q.Calculate the voltage drop of copper feeder 50 mm2 cable size,

60m length , 20.0 KVA, 230 V,1-phase. (Mention Ref. PLZ).

I(rated)=20,000 (VA)/230V=87 A

V.D% =0.81 (mv/amp/m)* X 87 A X 60 m(length) X 100(%) /230,000 mV

= 1.84% (<3%, acceptable)**.

Q.Calculate the voltage drop of copper feeder 16 mm2 cable size,

60m length , 20.0 KVA, 380 V,3-phase. (Mention Ref. PLZ).

I(rated)=20,000 (VA)/ 400V / 1.732=28.9 A

V.D% =2.2 (mv/amp/m)* X 28.9 AX 60 m(length) X 100(%) / 400,000 mV

X 0.866 = 0.83% (<3% , acceptable)**.

References:

* As per Saudi cable table: (noted that: this table can be usedcommon for

single phase but for three phase multiply by 0.866. Also this values will be

minor changed between companies).

** As per NEC 2011(215.2(A): The voltage drop of a feeder or a branch

circuit is limited to 3 percent. However, the total voltage drop of a branch

circuit plus a feeder can reach 5 percent.

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