Crimping wire is a fast reliable way to put a removable connection on a wire, or join two wires together. The goal is to squeeze the barrel of the crimp connector around the wire, leaving a gas tight joint.
Unfortunately, these connections are often done incorrectly or using the wrong tools and leave a connection that can corrode and fail in a moist environment.
The first item is to use the correct tool. Unless you have done a lot of crimp connections the tool should have a ratchet to prevent you from opening the jaws until enough force, or a small enough diameter, is put on the connection. Most tools you can buy from the local hardware store are just cheep toys and will not do the job.
Some try to get around this by soldering the joint. This leaves the end of the wire leaving the crimp barrel brittle and susceptible to breakage. Also a bad crimp leaves voids that trap solder flux. Solder flux is an agent, usually in the solder, that cleans the metal surface to allow the solder to stick. What’s wrong with that, you ask. Flux is a corrosive and will degrade the joint over time, exactly what soldering was supposed to prevent. So the long and short, never solder crimp connections.
One option I have used on large crimp connections is to coat the inside of the connector barrel with an anti oxidation compound such as No-OX. This compound is made for electrical connections and can sometimes protect marginal joints from oxidizing and failing.
Ok, so you have the correct tool and you need to crimp more then one wire in the barrel. Two wires having the same diameter as one of another gauge can be crimped into a connector of the larger gauge. Two 14 AWG have the same diameter as an 8 AWG wire but might fit into a 10 AWG connector, or might not, depends on the stranding. But as long as the wire combination fits into the barrel AND the crimper for the gauge of the connector, not the wire, is used, the crimp should be good.
Let me put in a small word or two on stripping wire. Strip wire so there are no nicks or broken strands. A thermal stripper, one that melts off the PVC insulator
is the only sure way of doing this, but a good mechanical stripper in good repair
will also do good strips. Avoid the combination stripper/crimper as it will do neither well. I also strip one size larger then the wire, i.e. use the 12 AWG position to strip 14 AWG wire, to help prevent nicks. Inspect the strip after you do in, if there are broken strands at the point of the strip, do it again.
The strip length of the wire depends on the connector barrel length. The wire should go completely through the barrel and be visible on the non-insertion side of connector barrel. Don’t leave too much wire since it might interfere with the screw or fast-on and don’t leave to little. On a good joint the wire insulation should touch or almost touch the barrel, or be covered by the connectors insulator
Some crimp connector barrels (the good ones) don’t have a seam in the barrel, some do. If there is a seam, make sure the crimp nipple of the tool (if your tool has one) compresses the side of the barrel WITHOUT the seam. The other side should have a concave area to protect the seam from opening. Doing it the other way will leave your joints loose and prone to failure.
One last thing I do is to use heat-shrink on each connection. Put a length of heat-shrink tubing on the wire(s) before the crimp is made and shrink the tubing over the connector barrel and wire. I like to have the tubing at least twice as long as the connector barrel to act like a small strain relief on the wire to help eliminate sharp bends just at the barrel and thus, wire strand breakage. Since I always do this, I prefer the non-insulate crimp connectors to make it easier. These non-insulated types also make it easy to inspect the crimp after it is done. It’s just as easy t place heat-shrink over insulated connectors, just make sure the tubing will go over the insulator
, not just the wire.