I worked for Laing at Sizewell 'B' as an Electrician, then went again to work for Laing at second seven crossing to repair items like the 200 ton straddle carrier, to give me more wages I was employed as a foreman fitter, although my main job was electrical but it was a mixture, then a new electrical superintendent arrived, who realised there was a problem with insurance, and from that point whenever I went to do electrical work I had to have another electrician with me, not really a problem as most jobs needed two anyway, but even as an electrician when my job description did not call me an electrician I could not work on 230/400 volt equipment without some one officially employed as an electrician.
It was at some times funny, as I worked on quite technical equipment, and the guy I was with would say "Don't know how we will repair this." and I would reply don't worry I do, your here because of insurance you don't need to know anything.
I know I needed to measure frequency and voltage as most of what I worked on had its own generators, however it is rare to have voltage or frequency problems. However a simple plug in meter
will show both volts and frequency and should be enough to check the house supply is OK without use of a meter using wandering leads. A tester like this
will also likely help in your trade to see if solenoids are working, but anything more you would likely need to show it was required, with Y Plan 3 port valves being able to measure voltage may help, but only if you know the readings to expect.