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What is the advantage and disadvantage of combination of power transformers MV/LV grounding systems? Whether can we use the cable armor as grounding conductor in power system?
What is the advantage and disadvantage of combination of power transformers MV/LV grounding systems? Whether can we use the cable armor as grounding conductor in power system?

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[Hamid]

Section 250-118 of NEC: 1999 permits the use of various grounding conductors including tubular conduits used as cable raceway, cable armor and cable trays. Where grounding conductors are employed, it must be ensured that they are sized to withstand ground fault currents of value and duration appropriate to the circuit under consideration. If the conductor sizing is inadequate, the following may result: -Damage to the insulation of the ground conductor: In case the conductor is bare, insulation damage may occur in the phase conductor with which it is in contact. – Fusing of the ground conductor in extreme cases: Though this will result in the interruption of the fault current, it will cause the potential of the enclosure of the faulted equipment to rise beyond acceptable limits. The maximum temperature of the conductor during a fault can be calculated by the formula: For the purpose of reviewing the selection, the following value of Tm can be used: Copper fusing temperature 800

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