Can any one suggest an instrument I can use connected to a service (say for 1 month) to determine the electrical demand? This is specifically to comply with NEC 220.87(1)Exception. I was thinking of an E-mon Series 2000 but I think I would need more than one if I wanted to use it for both 240-1 and 208-3.

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.

John

9 out of 10 times I can just get the demand from the utility. Once in a while we need to add power to a sub-panelboard or transformer in a larger building or to a building without a demand meter (e.g. around here church buildings do not have demand meters).