carry coals to Newcastle
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.)
Categories:
Source: A Dictionary of American Idioms
