this is very basic.ISO 9002 is a system certification and UL approval is product certification wherein the UL performs certain tests on the product(as per their own standard)and gives certificate if it conforms .especially UL
is mandatory for high voltage application in US.whwrein UL gives guarntee for he complete insulation charactristics of an appliance with regard to the use of insulating materials used in an appliance
Further to your question UL also gives system certification like ISO 9002/QS9000 which is a different portfolio of UL.
