Bonding of metal air ducts required?

[PracticingEngineer]

NEC 250-104 & -110 seems to describe parameters around HVAC duct bonding but doesn't actually spit it out. Is it really required?

 

[condenseddave]

I believe that it is in certain instances, but I cannot recall exactly what conditions must exist to make it a requirement.

 

[Yeldud]

Bonding ductwork is not done in general practice for commercial work, because there is no hazard from static buildup inside the ductwork. However when handling combustible fumes, or dusts, there is a real hazard from static buildup in the ductwork, especially for non conducting plastic ductwork. Under these conditions one sometimes will make the duct interior static conducting, and will ground that inner liner, or one can run a grounding strap inside the duct to drain off static. On metal duct systems bonding straps may be needed to connect adjacent sections of duct accross the joints, due to the (relatively) high electrical resistance at the joint. Good luck

 

[VEEKRISH]

Had to do this once. We were ventilating a soap manufacturing plant. The alcohol fumes had to be vented out and this was done via a Lightning Arrester. The client insisted that we also bond the duct, just in case. Only one instance in the last twenty five years.
Normally for commercial sort of HVAC Ducts, there is no bonding done.

 

[FCIBSE]

We always bond them in Hong Kong in accordance to the British Standard(BS) to avoid possible electrical shock when maintenence personnel has to repair some electrical devices while he might have his body physically in touch with the duct.