Tater, as Jay mentioned, the string is just to help split the jacket, there's no electrical factor. Also, the outer jacket has no electrical function; it's simply there to prevent or at least delay the release of toxic fumes if a fire would reach the wire. The PVC(polyvinyl chloride)jacket on ordinary electrical cord can release poisonous dioxins and chlorine gas when burned which can combine with moisture to form hydrochloric acid.
National and local building and electrical codes(and their interpretation)vary in the U.S. and Canada.
This bit about fire insurance policies is said fairly often, but with little factual support. Coverage can't be denied or reduced unless some action on the part of the policyholder can be shown to be contributory negligence which caused or increased the amount of damage.
