STP in 480V MCC

session88

Member
Location
USA
Installing a CT onto a leg of a 3-Phase motor in 480VAC MCC Bucket. The CT is going to connect to PLC AI (analog input) Card.
Going to use #16 AWG STP (shielded twisted pair) from the CT out of the MCC to the PLC.
The 24VDC Analog CT Circuit is Loop-Powered (powered by the PLC's AI Card).

Does the STP Jacket need to be rated for a minimum of 480VAC since it will be very close to the 480VAC conductors inside the MCC ?

I assume 300.3(C)(1) applies to this installation ?

Or are there any exceptions in Article 725 that would allow the STP Jacket to be rated at 300 Volts ?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Installing a CT onto a leg of a 3-Phase motor in 480VAC MCC Bucket. The CT is going to connect to PLC AI (analog input) Card.
Going to use #16 AWG STP (shielded twisted pair) from the CT out of the MCC to the PLC.
The 24VDC Analog CT Circuit is Loop-Powered (powered by the PLC's AI Card).

Does the STP Jacket need to be rated for a minimum of 480VAC since it will be very close to the 480VAC conductors inside the MCC ?

I assume 300.3(C)(1) applies to this installation ?

Or are there any exceptions in Article 725 that would allow the STP Jacket to be rated at 300 Volts ?
Not really and that is why you have the informational note below that section. You need to look to Article 725 for that installation as 4-20 mA loops are typically Article 725, Class 2 circuits.

Informational Note No. 1:
See 725.136(A) for Class 2 and Class 3 circuit conductors.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Please recognize that what you have is not a bare CT (which is often used for metering) but a CT-based 4-20ma loop current transducer.
Among other things you do not need to use a shorting jumper on the CT when the loop circuit is disconnected.
That said, it probably makes no difference to the voltage limits of the insulation.

Sent from my Pixel 4a using Tapatalk
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Installing a CT onto a leg of a 3-Phase motor in 480VAC MCC Bucket. The CT is going to connect to PLC AI (analog input) Card.
Going to use #16 AWG STP (shielded twisted pair) from the CT out of the MCC to the PLC.
The 24VDC Analog CT Circuit is Loop-Powered (powered by the PLC's AI Card).

Does the STP Jacket need to be rated for a minimum of 480VAC since it will be very close to the 480VAC conductors inside the MCC ?

I assume 300.3(C)(1) applies to this installation ?

Or are there any exceptions in Article 725 that would allow the STP Jacket to be rated at 300 Volts ?
Depends on how close they are
 
Top