Size of earthing conductor in rotating machines

Earthing connection

• Each machine is provided with earthing terminal however, the machine shall be neither earthed nor provided earth terminal when
• They fitted with supplementary insulation
• They have rated voltage up to 50 V AC or 120 V DC and are intended to do SELV circuit. 
• If the machine rating greater than 50 V AC or 120 V DC but not exceeding 1000 V AC or 1500 V DC, the terminal for earthing conductor is provided in the terminal box. 
• If the rating of machine greater than 100 kW or 100 kVA, the earthing terminal shall be provided on the frame.
• If the rotor winding and bearing of a machine is insulated, the shaft shall be electrically connected with earthing terminal unless the manufacture provided separate protection for it.

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Size of earthing conductor

The size of earthing conductor

• That of live conductor if the cross-section area of live conductor less than 25 mm²
• 25 mm² if the cross-section area of live conductor lies between 25 mm² and 50 mm²
• 50% that of live conductor if the cross-section area of live conductor exceeds 50 mm²

Cross section area of earthing conductor

Cross section area of live conductor ( mm2 )	Cross section area of earthing conductor ( mm2 )
4	4
6	6
10	10
16	16
25	25
35	25
50	25
70	35
95	50
120	70
150	70
185	95
240	120
300	150
400	185