ground ring circuit design

[james_mcquade]

i have an application in which i need some assistance please. the system is 480 volts 3 phase, 1 hp motors. wires for 10 motors will be run in (1)emt conduit. i know to derate for temperature and current carrying wires, but i am working with others and we are trying to reduce installation costs.
we have typically run a ground wire for every motor, but are interested on other options.

1. if we used 1 ground wire for all 10 motors, what would the conductor size be? i think it would be 10 motors * 2.1 amps = 21 amps or a #10 wire.
2. another suggestion is to run a ground ring loop. does anyone have an idea on how to compute the ground wire size?

thank you in advance.

james

 

[bob]

Re: ground ring circuit design

James

1. if we used 1 ground wire for all 10 motors, what would the conductor size be? i think it would be 10 motors * 2.1 amps = 21 amps or a #10 wire.

The EGC is based on table 250.122 not on the FLA of the motor. You could run one circuit for all 10 motors and use the tap rules to connect each motor to the circuit. If you used a 30 or 40 amp
breaker for that circuit the EGC would be #10 cu.

 

[james_mcquade]

Re: ground ring circuit design

bob,
thanks for your reply. i don't know what i was thinking when i posted my question.
james