Allan Short time harmonics may ruin capacitors, cables when near-resonance exists.
Motors have large thermal time constants and can stand momentary harmonics so do transformers.
The big problem is with communication circuits and EMI from raised neutral potential. For these last two I feel lost. In all of my work, such is very hard to correlate, but when done yields some really interesting results. The results are also very specific to the system under study, and have not had a broad application. To specify voltage and current limits with this in mind is difficult at best.