On Fri, Oct 31, 2008 at 3:02 PM, Ruben J=F6nsson wrote: > My impression about the UL standard and mark (or other north american sta= ndards > for electrical industrial or domestic equipment) is that it is more cente= red > around fire hazard than electric shock hazard (compared to european > counterparts). A 24V device that is not designed correctly could very well > burst into flames but it still might be perfectly safe concernig electric= al > shock. > > This would imply that also 24V devices needs a UL mark. Is this correct? = Where > is the lower limits for exemption? I guess it would be an energy or power= limit > rather than just a voltage in this case. As Ken as replied, it all depends on the product and applicable standard (UL60950 for IT, UL508 for industrial control). UL examination is more than the Creepage/clearance things. Enclosure (material and construction) plays a big part as well. When it comes to the electrical examination on the PCB, yes there are thing like Class 2 power supply, limit energy circuit, limit current/limit voltage circuit, etc, which will help to reduce the examination of creepage/clearance. One very important thing is to choose UL recognized components for the critical parts of the device (plastics, voltage limiting device, current limiting device, transformers, etc). Xiaofan -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist