The E-mon requires a voltage reference, as do all meters that I am aware of.
There are KW/KWHr recorders available (buy or rent) that will do what is needed for 220-87 Exc.
This info is available here (NJ) from the utility companies. That info is acceptable for NEC compliance, and should be easy to obtain, IF the job you are involved in has utility power.
GE rental is a source for rental test equip; as are many others if you Google.
WW Grainger has recording test equip available if you want to go that route.