Some computer and receptacle loads may be non-linear, by I don't think there are enough to worry about in a typical office building. I think manufacturers have blown this issue out of proportion in an attempt to sell more expensive stuff. And many engineers have jumped on the bandwagon.
I'm not saying non-linear loads are never a problem, but its just not common enough to apply to an average service or feeder.
Even electronic lights ballasts usually only have 10% or 20% THD, so I wouldn't even consider those nonlinear.
Steve
I've had to deal with some neutral overloading problems due to non-linear loads. One of them was in a very up-market hotel in the Middle East where a substantial proportion of the load was non-linear single-phase.
In many parts of the world, LV distribution is from a wye connected distribution transformer which provides 400V 3-phase and 230V single phase (to neutral) or similar. Generally, the system will be designed to try to ensure reasonable balance on each of the three phases,
Non-linear single-phase loads generally have high third harmonic content. At three times fundamental, this harmonic (and others) add in the neutral. And that can be a problem.
Would this translate to a typical office?
Probably.
I looked at our current waveform at home today and I tried to make it look like a typical small office.
A couple of computers, some electronic ballasts, some halogens, a couple of LCD displays, some ceiling fans, printers..
A bigger office would just have more of everything but that doesn't invalidate my point.
THD was more than 40%.