Grounding for well pump motors

[yloylo]

Working on a project where I have a multiple well pumps located 150ft apart, where the nearest motor is 300ft from the MCC and the furthest motor is 700ft. I have sized the motor cables (3 conductors & ground) appropriately based on NEC.

My question is that due to the cable lengths for each motor, is it required to have a ground rod at each motor for an equipment ground since my closest service ground is back at the MCC (700ft away)??



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[fc]

What would the ground rod be used for or what would it due for you? I like the metal casing better but for what I don't know.It would never trip the circuit breaker.
If you up your conductor size due to the distance then you would also up your EGC conductor because of the distance. That will take care of your equipment ground.

 

[yloylo]

Part of the concern is lighting. These motors are located out in the woods. If there is a lightning strike near the motor, my closest path to ground is ECG going back to the MCC panel at ~700ft away.

I want to install ground rods for this reason, but I didn't' know if there is an NEC requirement for this or not.

 

[fc]

It's not required but why would you drive a ground rod when the metal casing is already in the ground? I am taking for granted that you have metal casing in the ground. If you don't you can install a ground rod for lightning.

 

[bphgravity]

FC has good advice. Make sure you increased the EGC to the equipment proportionately to the increae in the ungrounded conductors. This will ensure the ground-fault path remains effective.

 

[yloylo]

Thanks for the assistance. This has been helpful

 

[tom baker]

If you run your motor branch circuit and its EGC thru a ten foot lenght of RMC, bonded at one end only, that will create an impedance choke on the branch circuit and its EGC and limit the lightning current back to the MCC.

 

[yloylo]

For each of these motors, I'm using VFD rated Armor cabling which is direct buried. Does this compensate for the 10ft of RMC?

The armored cable is sized at 4/0, 3 conductor, and has 3 #8AWG grounds. The well pump is submerged at 75ft below the ground. The motor leads for the pump is connected to the secondary of a fiberglass (NEMA4X) non-fused disconnect that is mounted on a concrete pad.

 

[pierre]

Would you be able to provide the brand and identification of the cable type you are direct burying?

 

[yloylo]

The type of cable is CordFlex Armored VFD cable, UL Type MC HL, 600V, 90degC

3 Conductor with 3 ground wires, continuous corrugated aluminum sheath, PVC jacket.