Conductors of Different Systems

[tperry]

Hello,

My application is in a commercial building on the air handling unit mechanical floors. Performing the installation of VFD's and Motors.

Q: Can you have communication cable that is rated at 300VAC terminated in the VFD along with the main power for the VFD/Motor which is 480V 3PH? (According to 300.3 (C)(1) I cannot)

• I have been told that once you increase the voltage rating of the communication cable to 600VAC you loose plenum and riser rating.
• Is there an exception for VFD's?
• The way that I interpret 300.3 (C)(1) is "... the circuit voltage applied to any 'single' conductor..."

Thank you,

 

[Dennis Alwon]

The voltage on any one conductor on a 480/277 is 277V so a 300 volt insulation should be okay. Now you have to comply with 725.136

 

[iwire]

I really do not know the answer here but I have my doubts it is the voltage to ground they are worried about. How would that play out with ungrounded systems?

IMO all the conductors would have to rated at least 480 volts.