I have to replace wiring in a power meter box in an apartment building. There're four really beefy wires running vertically through the whole building and each wire has a short stripped segment inside the meter box and a steel connector is attached to the stripped part. Each connector consists of two plates aligned in parallel and the wire is placed between them and as the plates are connected with screws they are forced onto the wire and have electrical contact with the wire.
Each plate also has extra holes with threading and I have to attach branch wires that go to the actual load to the connector by warping a ring on the branch wire end and attaching that ring to the hole on the connector with a screw.
The problem is the connectors surface is of recognizable almost black color that steel parts get when they are exposed to mild humid air for long time - looks like result of oxidation treatment. I suppose this is not very good for electrical contact and I have to clean the connector surface where a wire will touch it.
How do I clean a steel connector surface? Do I just use fine sandpaper or do I need anything else?