Английский словарь американских идиом - carry coals to newcastle

{v. phr.} To do something unnecessary; bring or furnish something of which there is plenty. * /The man who waters his grass after a good rain is carrying coals to Newcastle./ * /Joe was carrying coals to Newcastle when he told the doctor how to cure a cold./ (Newcastle is an English city near many coal mines, and coal is sent out from there to other places.)