in is acceptable but on is definitely the more common expression in this context why there is no why it's just one of those perverse idioms of english we can be on form but later in decline you might be instructed to do something when you are in receipt but you should on receipt the up and down conventions are even worse we cut down trees but then chop them up after dinner we wash up but to get rid of the suds we rinse down i could go on but the short answer is i don't know why i know copper is not the only material but that is the common expression especially when disambiguating against fibre optic the reason here is obvious it is by far the most common metal used for cables i don't really care if the article title gets changed but this is what i think it should be