Running Shielded PTC Wire in XP Conduit

cowski

Member
Location
New York
Occupation
Engineer
We're receiving a XP motor with PTCs rather than temperature switches. I asked for temperature switches but our partner in the EU did not accommodate.

The PTC seems like a thermistor and basically a analog signal. From what I can tell this is typically shielded, especially if it's run in the same conduit as the motor leads, see https://www.eng-tips.com/viewthread.cfm?qid=109074.

Is it acceptable to run a shielded 2 conductor cable in the same conduit as the motor conductors? Obviously the shield would only be grounded at one end. I'm assuming the shield would have to be trimmed back where the explosion proof seals are, so the wires can be separated and sealed.

It seems common to run PTCs intrinsically safe but that doesn't seem like an option in this case because it's embedded in the motor winding and very close to the high voltages therein. Maybe that's an argument for leaving it unshielded altogether...

Thanks,
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Not sure what part of Article 725 would permit you to place the temperature conductors in the same raceway as the power conductors.
 
You would usually need to have some cable segregation due to the different power levels of the temp cables and the power regardless of the cable shielding for noise reduction. One company I worked for had a standard where those 2 signal levels would be need to be 6" apart if both run in individual conduits
 

cowski

Member
Location
New York
Occupation
Engineer
Thanks. We ended up getting a motor with temperature switches rather than a PTC. We're running 460 AC to the temperature switches in the motor and back to a contactor in the control panel.

I'm a little worried about putting 460 on the temperature switches. Does anyone know if that's common? I need to verify that the temperature switches can handle that voltage.
 
Top