Were wires joined with twist-on connectors abraded and pre-twisted?
The integrity of a connection made with twist-on connectors is increased if the wires are first properly abraded to break up the oxide layer and coated with an oxide inhibitor. Unfortunately most twist-on connectors do not specify this as a requirement. The connection is also better if the wires were pre-twisted together with pliers before the twist-on connector was installed. One wiring practice is to push separate straight wires into a twist-on connector using the twisting action of the connector as the only means to join the two wires. This method is often used as it saves electricians a lot of time during the installation Most twist-on connectors specify that no pre-twisting is required, however, pre-twisting has proven to increase the integrity of the connection. Without pre-twisting, the effective wire-to-wire contact may be only a fraction of the wire-to-wire contact between pre-twisted wires. The relative motion between the two conductors is also decreased with pre-twisting, he
