HVAC Ducts

[kc8dxx]

We were recently reviewing a diaphragm pressure switch for an application, where the mounting location of the metal-cased switch was plastic. We decided in the end to move the switch from it's original location to a place where it was mounted on a grounded metal casing.

This got us to wondering about our heating ducts in houses. Are they connected in any way to earth ground? One would think so, we thought, considering the blowing air and dust might cause a buildup of static. I certainly don't recall seeing any wires in my house. I suppose the ducts are secured to the furnace, which has an equipment grounding conductor on it running to the breaker box. That's a pretty poor ground IMHO.

So I submit the question to the group. Are house HVAC ducts grounded?

 

[iwire]

It takes very little to ground against static buildup.

Any incidental contact with other grounded objects will do it.

 

[W6SJK]

Chances are they are grounded, allthough not very reliably, by the branch circuit feeding the furnace, unless there is perhaps a nonmetallic expansion/vibration joint... ?

 

[JohnJ0906]

Chances are they are grounded, allthough not very reliably, by the branch circuit feeding the furnace, unless there is perhaps a nonmetallic expansion/vibration joint... ?

I usually see these joints installed, keeps noise or vibration from the furnace from the duct work.