connectors
We need to splice or extend existing AWG 1 main service panel wires and the splice would be left open to rain. What kind of connectors that would create watertight waterproof splice?
I have this (but putting tape all over it would not create waterproof splice because water can leak in:
I finally found it in the WAGO online catalog WAGO 222-413 lever connector is listed for copper. There is no reference to aluminum. WAGO sells a joint compound in a syringe for injecting into these connectors and this made me hope that they were listed for solid aluminum, but it seems not so. I think it would work, but if it's not listed then one cannot use it for pigtailing aluminum wiring.
Your wire is #8 AWG, copper since it's a 40 amp circuit. So you need a connector that will fit that wire. The sizing on the connectors states what wires will fit in the individual holes in the connector. So in your question you have a connector that is rated for "1/0 - 14 AWG", it will handle a 14 AWG to a 1/0 AWG wire. Since your wire is a 8AWG, this connector would work. A sample wire chart is shown below.
Since these are expensive connectors, you want to get the smallest one that will accommodate the wire sizes you are using. There are other connectors available so you might want to ask another question about this and explain what you're connecting and you might get some better ideas.
Best Answer
I'd use a Burndy UGSKIT250
For this sort of outdoor/exposed-splice application (as you would find when splicing a triplex or quadruplex overhead feeder or service cable to riser wires in a mast), I would use a Burndy UGSKIT250 for the individual wire splices. This kit consists of a bare (uninsulated) mechnical splice suitable for 1AWG-250kcmil wire, either copper or aluminum, and a length of heavy wall heat shrink tubing to be shrunk over the top of the splice for waterproofing. It is UL listed for use outdoors (and even in direct burial applications), and does not require any sort of junction box.