Bonding cable sheath one side

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powerplay

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A three phase 600 volt dock leveller had been hooked up by a "teck" cable (copper conductors wrapped in armour and rubber jacket) The motor connection box under the Leveller is bonded by the bare wire and bonds the sheath, but the other end of the cable is sleeved in PVC that rises up the floor into the plastic control box with the sheath stripped back in the PVC and only the 3 conductors and bond coming into the plastic control box. Everything is bonded, but the sheath is supposed to be bonded on both sides. If both sides are required to be bonded, I doubt many would put a grounding bushing where it connects to the plastic box. It is safe, functions, and seems the way people make it work. Any issues/feedback with this installation? Thanks again!
 
Floating sheath

Floating sheath

powerplay said:
A three phase 600 volt dock leveller had been hooked up by a "teck" cable (copper conductors wrapped in armour and rubber jacket) The motor connection box under the Leveller is bonded by the bare wire and bonds the sheath, but the other end of the cable is sleeved in PVC that rises up the floor into the plastic control box with the sheath stripped back in the PVC and only the 3 conductors and bond coming into the plastic control box. Everything is bonded, but the sheath is supposed to be bonded on both sides. If both sides are required to be bonded, I doubt many would put a grounding bushing where it connects to the plastic box. It is safe, functions, and seems the way people make it work. Any issues/feedback with this installation? Thanks again!
Click to expand...

What you have described is a floating shield with an EGC ending at the device within a plastic enclosure. This is acceptable for RFI/EMI protection for the cable in most cases unless the manufacturer has specified a termination connection at the circuit end in question.
 
powerplay said:
A three phase 600 volt dock leveller had been hooked up by a "teck" cable (copper conductors wrapped in armour and rubber jacket) The motor connection box under the Leveller is bonded by the bare wire and bonds the sheath, but the other end of the cable is sleeved in PVC that rises up the floor into the plastic control box with the sheath stripped back in the PVC and only the 3 conductors and bond coming into the plastic control box. Everything is bonded, but the sheath is supposed to be bonded on both sides. If both sides are required to be bonded, I doubt many would put a grounding bushing where it connects to the plastic box. It is safe, functions, and seems the way people make it work. Any issues/feedback with this installation? Thanks again!
Click to expand...
power -
I'm guessing "teck" is MC-HL or very similar. I'm also guessing the installation is Canadian - cause "teck" is mostly a Canadian term and the service is 600V. Also guessing the sheath is aluminum.

Yes, the sheath is susposed to be bonded on both ends. The fitting will be what ever corresponds to a CH TMC or TMCX and that is what one would put the grounding bushing on. As for not bonding both ends, if sheath is Al, it doesn't matter much, the internal CU grounding conductors - just not good practice. If steel, both ends have to be bonded. Otherwise, the unbonded ferrous sheath acts as a choke and cuts back on the SSC - Bad Practice. What you are describing is no different than conduits coming up into an open bottom MCC. Normal practice is hit each one with a bonding conductor.

I put in a lot of MC-HL. If the connectors don't screw into a metal box, then the connector gets a bonding bushing - same as one would do to a metalic conduit.

gndrod said:
What you have described is a floating shield with an EGC ending at the device within a plastic enclosure. This is acceptable for RFI/EMI protection for the cable in most cases unless the manufacturer has specified a termination connection at the circuit end in question.
Click to expand...
What RFI/EMI? It is a 60 hz power cable from a motor starter to a motor. In a few cases, VFD mfgs request a cable sheath be bonded on only one end - rare and not this. Not bonding both ends of the sheath is no different than not bonding both ends of a metalic conduit - uncommon.

ghostbuster said:
The cable sheath grounds are isolated at one end to prevent inductive sheath currents from flowing and heating up the cable-check your code books for more info
Click to expand...
Why would there be inductive sheath currents? Shouldn't be any different that an installation in metalic conduit.

gndrod said:
Also check your Radio Engineers Handbook for effects of ground loops and signal cross-coupling.
Click to expand...
60Hz, motor starter to motor. This is not an ARRL issue.

ice
 
iceworm said:
power -
I'm guessing "teck" is MC-HL or very similar. I'm also guessing the installation is Canadian - cause "teck" is mostly a Canadian term and the service is 600V. Also guessing the sheath is aluminum.

Yes, the sheath is susposed to be bonded on both ends. The fitting will be what ever corresponds to a CH TMC or TMCX and that is what one would put the grounding bushing on. As for not bonding both ends, if sheath is Al, it doesn't matter much, the internal CU grounding conductors - just not good practice. If steel, both ends have to be bonded. Otherwise, the unbonded ferrous sheath acts as a choke and cuts back on the SSC - Bad Practice. What you are describing is no different than conduits coming up into an open bottom MCC. Normal practice is hit each one with a bonding conductor.

I put in a lot of MC-HL. If the connectors don't screw into a metal box, then the connector gets a bonding bushing - same as one would do to a metalic conduit.


What RFI/EMI? It is a 60 hz power cable from a motor starter to a motor. In a few cases, VFD mfgs request a cable sheath be bonded on only one end - rare and not this. Not bonding both ends of the sheath is no different than not bonding both ends of a metalic conduit - uncommon.


Why would there be inductive sheath currents? Shouldn't be any different that an installation in metalic conduit.


60Hz, motor starter to motor. This is not an ARRL issue.

ice
Click to expand...

Yer spelling is as good as my subtle humor. Thanks.
 
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