Externally bonding industrial motors.

[Dsg319]

I know there’s probably a good reason and I just don’t know it.

Here is the work setting. Natural gas facilities,
Station ground/bonding wire an insulated conductor routed underground bonded to all steel and equipment. Usually have some magnesium anodes in the system too. And havnt dug yet in the drawings to clarify this but most time this station ground is bonded to the GES. But this place is off grid and gets it power from a capstone (which I believe is like a micro turbine. So I’m not sure if the grounding system-is bonded to that power supplys GEC or not. Havnt yet seen if it is delta/wye. For have just been in the roughing in stage conduit,cable tray,etc

But regardless of the fact I’m trying to wrap my head around the use and point of this. We have some motors running some big cooling fans and they call for the grounding/bonding system to also be tied onto the motor itself(externally). Is there something special that it does that a EGC inside the motor doesn’t do?

 

[zbang]

Only WAGs, here-
Are the motors on VFDs?
Are they attractive targets for lightning (or generate static electricity)?

 

[Dsg319]

Only WAGs, here-
Are the motors on VFDs?
Are they attractive targets for lightning (or generate static electricity)?

They are on VFDs. And as for generating static I do not know. Maybe that’s why they spec it out?. And for lighting the motor is in a big metal cage (cooler) that is also tied into the station grounding/bonding system.

 

[Dsg319]

I as well could be thinking to much into it and may simply be just a means of electrically bonding the motor directly to the grid and surrounding steel.

 

[SSDriver]

A lot of gas and petroleum facilities want it on the outside so it can be verified and inspected without opening things up

 

[tom baker]

Or it could be an old spec from the 480 delta service days, before 377/480 with neutral and EGC

 

[augie47]

One of the industrial firms I worked with had a requirement for external grounding of motors and an operators checklist
included verifying the ground was intact. Their reasoning was a "safety feature" recognizing the importance of grounding and the fact that internal grounding could not be verified by a "sight" inspection.

 

[petersonra]

There is no really good reason for these kind of things. It is in the spec so everyone does it but no one can tell you why.

 

[petersonra]

One of the industrial firms I worked with had a requirement for external grounding of motors and an operators checklist
included verifying the ground was intact. Their reasoning was a "safety feature" recognizing the importance of grounding and the fact that internal grounding could not be verified by a "sight" inspection.

You can't verify if the circuit conductors have come loose with a "sight" inspection either.