Contact wire connections between a wired lug and the buss bar should be very low ohms, like 0.1 ohms or less, low enough to not be measurable by most meters is what I think. You can have a good connection, if the metals are clean and the screw is tight and the lug is well secured to the wire. Certainly should not get too warm warm when current is flowing, resistance creates heat, And the wires and buss should be well sized for the current flow.