Residual Voltage Warning

Merry Christmas
A

Ashu

Member
Location
Hunt Valley, USA
Occupation
Electrical Engineer
We have a drive in our electrical enclosure which has a residual voltage warning label before servicing. A UL inspector mentioned that we need to have a similar warning label on the enclosure where this drive is mounted per NFPA 79 2024, section 6.5.1 below:
6.5 Protection Against Residual Voltages.
6.5.1 Live parts having a residual voltage greater than 60 volts
after the supply has been disconnected shall be reduced to
60 volts or less within 5 seconds after disconnection of the
supply voltage.
Exception No. 1: Exempted from this requirement are components
having a stored charge of 60 microcoulombs or less.
Exception No. 2: Where such a provision would interfere with the
functioning of the equipment, a durable safety sign drawing attention
to the hazard and stating the delay required before entry to the enclosure
is allowed shall be displayed at an easily visible location on or immediately
adjacent to the enclosure containing the capacitance.

I believe this code applies to the enclosure of the device which has the residual voltage (i.e. drive enclosure which already has this label as shown in the picture) and not that it is also required to the enclosure where this device is mounted. Will appreciate advise on this matter.
 

Attachments

  • Drive_REsidual voltage.jpg
    Drive_REsidual voltage.jpg
    33.8 KB · Views: 2
YASKAWA dealer here: The residual is the charged cap bank connect to the bus. Most drives are designed to dissipate in about 3-4 min. I've been hit by residual drive outputs. Ouch.
 
Although the drive is containing the capacitance, the enclosure is containing the entire drive, which therefore the enclosure is also containing the capacitance. If removing the enclosure cover leaves exposed live parts that are energized by the capacitors, I think you need the warning label on the enclosure.

Is anyone aware of a similar requirement for remote enclosures that have live parts energized due to capacitance? I've seen drives where the branch circuit conductors remain energized due to the capacitors, so the panelboard with the branch circuit breaker has the load side of breaker remain energized for a few minutes after the breaker is switched off.
 
I agree with label on the enclosure. I'm not sure if dead grounding the leads will damage the drive. I've never tried that, I just wait.
 
You must log in or register to reply here.
Top