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Posted By Topic: Flexible cables

Aug 31 2017 08:36

Beyond compliance with section 3.3 External Influences, is there anywhere that explicitly requires motor tails to be done in flex rather than installation wiring?

Situation is 3ph DOL motor attached to a conveyor. What appears to be 7 strand circular TPS comes out of floor trunking to an isolator mounted on the conveyor. The same cable runs from the isolator to the motor terminal box. The cable is sheathed in flexible conduit and clipped to the machine at wide intervals.

I'm not so worried about the run to the isolator although, personally I would have used an enclosed conduit and conduit glands. I'm more concerned about the tail to the motor. It would never have occurred to me to use anything other than a fine stranded flexible cable given movement/vibration and that the motor could be removed during maintenance. I'd like it changed but wondering whether section 3.3 is my only support.

Aug 31 2017 08:57

There's no specific requirement for flex.

Given the description, movement isn't likely to be an issue and if there's enough vibration to matter then something's wrong with the conveyor

When I was doing industrial work, most of the motors "tails" were wired with standard cable, either TPS or conduit wire, in flexible metal conduit. Some were in Pyro (single strand), but always with a vibration loop (same as is often done for pipework). We never had a cabling problem from vibration.


Aug 31 2017 10:04

Thanks AlecK. My experience is largely manufacture for export to UL508 standards. Flex was a given. Made sense and I never questioned it. We applied the same standards to local jobs.