MOV ELECTRICAL GROUND

[tvtran]

HI, I AM LAYING OUT A GROUND SYSTEM FOR A METER PUMP STATION. I HAVE A GROUND RING SYSTEM FOR THE PCR, TRANSFORMER AND METER SKID. I ALSO HAVE SOME MOV'S (MOTOR OPERATED VALVES) LOCATED ALL AROUND THE STATION. THE MOV'S ARE 480V AND IS DRAWING 5 AMPS. THE MOV'S HAVE GROUNDING CONDUCTOR PROVIDED WITH THE MOTOR FEEDER 12/4 THHN THAT IS CONNECTED TO THE PANEL INSIDE THE PCR AND IS CONNECTED TO THE GROUND RING SYSTEM, DO I STILL HAVE TO CONNECT A GROUND FROM THE MOV HOUSING TO THE GROUND RING SYSTEM.

 

[IRstuff]

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[waross]

It depends:
What are you pumping??
It this is a petro-chemical plant in North America, the American Petroleum Institute (API) codes may apply. If so, the API code may require an external ground conductor significantly larger than the NEC minimum.
Note: The purpose of the NEC ground is to provide a path for ground current that will cause operation of the protective devices in the event of a ground fault in the motor.
However, in the event of a ground fault the supply conductor and the equipment grounding conductor may for a voltage divider. The equipment grounding conductor is generally smaller than the phase conductors. In the worst instance the touch voltage on the frame of the motor may rise to over half the line to ground/neutral voltage of the circuit until the breaker or fuse clears the circuit. That is over half of 277 Volts. That may be both a life hazard and a possible ignition hazard.
The API code addresses this possible threat by requiring an additional equipment grounding conductor of sufficient size to limit the touch potential to a safe level.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tvtran]

Thanks for your reply Waross. Replying your question, "What are you pumping??", we are dealing with Crude oil. However, the equipment I am grounding are MOV's (motor operated valves). These motor valves are not used for throttling purposes as they serve mainly On-Off service application. The MOV's are 480V and is drawing 5 Amps. The MOV's have grounding conductor provided with the motor feeder 12/4 THHN cable that is connected to the panel inside the PCR and is connected to the ground ring system. Do I still have to connect a separate ground from the MOV housing to the ground ring system?

Tran

 

[waross]

That is a code issue and I don't have the API codes.
Hopefully someone with a copy of the API codes will post in.


Bill
--------------------
"Why not the best?"
Jimmy Carter