[alduin32]

A first thing to test would be that your voltages are nominal, but the exact details depend on how many phases are coming from the transformer, how they are wired, and whether you are on a TT, TN-C-S or other kind of grounding system, which depends mostly on where you live. Also, you need to take your voltages both at low impedance (simulates a load) and at high impedance (negligible load, "classical" meters are generally high impedance).

Generally, you want to measure the voltage difference between live and neutral depending on the load. However, depending on the tools you have access to, taking this reading properly can be a bit tricky both because simple high-impendance multimeters can easily be tricked by ghost voltages caused by bad connections and inductions from other cables, and also because understanding what to measure requires knowing how is the electrical system wired.

If you know you are in a TT system with 240V between Live/Neutral, I can tell my procedure for inspecting neutrals. In a two-pole TN-C-S system with 120V between L1/Neutral and 240V between L1/L2, I suppose it would be similar, expect that we'd have to do more tests (both L1 and L2 to neutral, and I imagine also L1 to L2).

EDIT: a first simple check to do is to check, using any multimeter, if there is voltage drop in your office when the hairdryer is in use.

[globnomulous]

Thanks so much for the write-up!