120 volt lighting contactors humming loudly

[Smart $]

Dirt/swarf between the pole faces maybe......

Hardly ever see that word used.

 

[Smart $]

We are talking about three brand new Square D contactors, I think it is highly unlikely they all shipped with defects.

I agree. Not saying they will not hum at all when installed properly, but three different hums IMO indicate an installation-related cause.

 

[big john]

We are talking about three brand new Square D contactors, I think it is highly unlikely they all shipped with defects.

Agreed, it is unlikely, but the only way to troubleshoot is process of elimination.

 

[MiElectrician]

Would you guys run a pair of solid state relays in this situation?