UL Question about Clearance vs Creepage

[Julio Chadrone]

Does Clearance require line of sight or is it any space in free air matter even if the two metal parts are separated by a tall insulated part and electrons would have to make two 90 degree turns to wrap around. If so what is the difference between creepage, since creepage is the shortest path which would be the same path as clearance?

 

[JoeStillman]

Are you talking about working space clearance, or air insulation?

 

[jim dungar]

I look at clearance as the total distance through air including angles, while creepage is the total distance across a surface.

Clearance often deals with the ability of a foreign body to touch two places at one time, such as dropping a screw onto a terminal block. Creepage deals with accumulation of material which can create a conductive path.

 

[Julio Chadrone]

Are you talking about working space clearance, or air insulation?

I was talking about distance from one live metal and ground or live metal of the opposite polarity

 

[Jraef]

In UL considerations, it is distance between live parts, both across a surface (2 inches) and air spacing (1 inch).

That's why some European breakers being sold now in the US have to be installed with "phase barriers" (fins) between the poles. They are DESIGNED for max. 415V to IEC specs, but end up without enough surface area and air distance between live parts per UL 489 and CSA specs for 480-600V in North America. Example: