I am working with an electrical socket and I need extra length on the ground wire. It doesn't seem unreasonable that I can attach an extra three inches to the existing one and attach it with a copper wire crimp. Does anyone see a problem with this?
I have no extra slack on the rest of the wires, so I am not able to pull it through any further.
Technically, you should twist the extension bare ground wire to the short one and secure it with one of the copper crimps like you have pictured. A wire nut certainly would work , but it should be green. Practically speaking, either way will work and be safe, just a matter if you want to follow current NEC standards.
As an apprentice electrician... years ago, I was trained to use these crimp sleeves on all of our residential installs. So, I have and still do, use these crimp sleeves for the purpose you described. The important thing is to install the device per the manufacturers instructions. There is a prescribed method for installing these things and you have to follow the method or no you shouldn't use it for the purpose you described.
the following link is a cut sheet for the "Ideal" brand product and doesnt show the method of installation,
https://rexel-cdn.com/Products/Ideal/30-410.pdf?i=43A07F9B-9189-41EC-90AF-6D1F4AA0126B
This link shows the installation instructions which should accompany the sleeves when you purchased them. https://media.distributordatasolutions.com/ideal/2018q1/936d9a932e1d05817dd91ffa8235e01ed2058e31.pdf
Basically, you spin your ground wires together 3 times using either the crimp tool or a pair of linemen's then crimp the sleeve over the twisted wires.
Based on my research the anawere is no. There are crimp sleeves that are copper with tin plating which I believe would eliminate the dissimilar metal issue of joining aluminum to copper wire but, you still have the issue of aluminum wires excessive expansion/contraction properties when heated by current that, I believe, is why there isn't any wirenut currently approved by CSPC OR NEC to join aluminum wires period. The only crimp system is copalum cold weld crimp pigtail system by Amp-tyco but it's only available by specially licensed installers. Your only certified way to join your two aluminum wires to a copper pigtail is using alumicon connectors that srew clamp each wire in a dedicated port.
I historically used the abrasion in the presence or non flammable anti oxidant grease but it is slow and not a preferred method, any more, because of the aluminum expansion contraction consideration.
My personal approach when it is impossible to either expand the box ( i.e. phenolic 1 gang boxes or fit 3 alumicon 3 port connectors in the box, and since the ground shouldn't be seeing any persistent current, is to coat the two ground wirers with non flsmable antioxidan, abraid them with #240 emery cloth (also coated with the grease) and then use 1 or 2 tin coated copper crimp sleave to crimp the 2 aluminum wieres to a copper pigtail which was already connected to the recpticle ground, fold in the wirers and device into the box and call it a day. There is a 1/2" box Extender ring if you don't mind turning the recepticle to a raised one.
