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Bonding wire size for a 4160V motor. For motor to skid (not EGC)

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    Bonding wire size for a 4160V motor. For motor to skid (not EGC)

    Could use some help. Not well versed in the 4160V world...

    what is is the correct wire size for bonding the motor to the skid that it’s mounted on (bonding around vibration isolation bars, customer request). this is not the EGC, the end customer is responsible for powering the motor. But I’d like to have the same size wire as the EGC to appease the customer. So I don’t know what their overcurrent protection device or settings are... looking at 250.122 it looks like I should use 10awg?

    motor data plate
    Click image for larger version

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    I have no direct experience with this sort of application, but wouldn't something like a braided bonding jumper be the 'ideal' solution?

    If so, then the effective cross section is probably so large that the minimum wire size becomes moot.

    For example:

    -Jon (who is questioning rather than suggesting)


      It would be ideal. And I even bought some braided straps for it. But the motor has a compression clamp on the side of it for regular wire, and that's what they're making us use...

      Can take a picture of it when i get back into the office tomorrow, don't have one of it on my phone


        250.112(K) Skid-Mounted Equipment. Permanently mounted electrical equipment and skids shall be connected to the equipment grounding conductor sized as required by 250.122.

        250.122 is essentially the EGC size.


          If it’s a supplemental ground and not required there is no minimum size. Need to know grounding scheme though. If it’s high resistance grounded, particularly with a ground continuity monitor, this can potentially cause it not to work correctly. High resistance grounds are the standard at 4160 instead of solidly grounded.

          Sent from my iPhone using Tapatalk


            I think I had a type when i said 250.122. (Was going from memory)
            I dont have my laptop at the moment to pull up the sections, but if i read it correctly it said it is sized off the over current set point (35amp fuse, or whatever it may be), but I dont know, and likely wont get any of the customers info.
            I dont know what the scheme is, it's on the customer at this point (till they show up next week haha). Its just a motor/pump sitting on a skid just big enough for the combo. It's for a Hydraulic pump, which has other motors and heaters that are all 480V. I never dealt with HGR, but they never mentioned any requirements in their spec sheets


              Originally posted by emiller233 View Post
              and likely wont get any of the customers info.
              Determine the largest OCPD that could serve the skid (the customer may choose smaller, but who cares) and then choose bonding conductor based on table 250.122.

              Whether it is solidly grounded or resistance grounded, it doesn't matter. Resistance grounded is only worth something for the first fault, then every fault after that, it is solidly grounded so the conductor is sized the same.


                Yup. And resistance grounding doesn't change your bonding requirements; it just changes how the system neutral is connected to your grounded/bonded metal.

                To the op:
                You may be able to get a bonding strap with a 'pin' termination on one side. One could certainly stuff braid into a ferrule (I've done this for some shielded cables in the lab) but for your situation something Jerry rigged is likely not appropriate.