equip ground size for 150 hp 480v 3 phase mtr

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Eric42

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I have a customer who thinks that the equipment ground should be the same size as the current carrying conductors.
 
Re: equip ground size for 150 hp 480v 3 phase mtr

Try explaining that motor wiring is sized to continuously carry full load while the EGC is sized to safely carry fault current for the short time until the breaker trips.

EGC is also sized to keep the voltage drop due to fault currents flowing in the EGC below harmful levels. Motor conductors are sized to keep voltage drop at full load or during starting within a few %.

Different criteria, different applications on the same motor lead to different wire sizes for EGC and motor conductors.
 
Re: equip ground size for 150 hp 480v 3 phase mtr

Originally posted by Eric42:
I have a customer who thinks that the equipment ground should be the same size as the current carrying conductors.
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If they want to pay for it go ahead and give to them. :)

Of course that can be tough to do if it is a cable job. ;)
 
Re: equip ground size for 150 hp 480v 3 phase mtr

Originally posted by Eric42:
I have a customer who thinks that the equipment ground should be the same size as the current carrying conductors.
Click to expand...
charge him extra and forget about it. not worth arguing over something that is a safe installation, but exceeds requirements.

In many cases a seperate EGC is not even needed. the conduit can serve as the egc.
 
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