A temporary protective cover for a junction box has a sheet-like rectangular body with cleats at top and bottom ends. The cleats are flange-like formations bent at preferably non-right angles designed to press against embossments inside the cavity of a junction box. One or both cleats may be fitted with a notch to facilitate overlapping placement to accommodate large-size junction boxes. A stop tab extends laterally outwardly from each cleat and serves to limit penetration of the covering into the cavity of a junction box. One or two small removal holes are located in the body of the cover, near to the cleats, to facilitate removal from a junction box.