Re: what is the difference between a union ground and a eric
Not famaliar with either term, but here's my best guess. I believe that both of those terms refer to the manner in which the grounding electrode conductor is terminated to the grounding electrode.
"Union ground", short for Penn-Union, maker of the typical acorn type grounding clamp and other miscellaneous compression connectors for grounding.
"ericson ground", possibly referring to Erico, manufacturer of the CadWeld system of exothermic weld type grounding and bonding terminations.