35 reels of electrical cable have been stolen from a building site in Desborough.
The break in happened on Christopher Close overnight between Monday, 27 and Tuesday, 28 July.
A generator, power leads, a power adaptor and a bag of tools were also taken.
Witnesses, or anyone else who is offered similar items for sale in suspicious circumstances, can call Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111 or use the anonymous online form at www.crimestoppers-uk.org.