Most electricians have a MFT (multi function tester) and it has the specific capabilities you need for dead and live testing an electrical supply system:
- High voltage DC insulation resistance test (typically 0.1-200M or more, at 250/500/1000V)
- Low resistance measurement at medium test current (typically 0.01 to 100 ohm at up to 0.2A)
- AC Voltage (typically just 1kV range)
- Earth loop fault impedance (Zs/Ze)
- RCD trip time and trip current
Some have a few more features (e.g. EV specific test, earth rod testing of ground impedance, etc) and price varies from about £500 to about £2000 depending on options. What MFT don't do is current measurement as a general rule, most electricians have a separate clamp-on ammeter for that so no issue of probe current carrying capacity, interrupting a running supply, etc.
For electronics work, and sometimes to fill in gaps for the MFT's range, you get a multi-meter. Typically they offer:
- Voltage (AC & DC, usually from 0.1V max to 500-1kV max selectable)
- Current (AC & DC often microamps to 0.2A on one socket and to 10A on another)
- Ohms (typically from 0.1 ohm to 10M ohm but good resolution in all ranges)
Many now offer added features (diode voltage drop, capacitance, frequency, temperature with thermocouple probe, etc) but if you are planning on using one for working on high energy systems (i.e. mains supply) you
must get one that is at least CAT-III rated to 300V, and ideally more (CAT-IV to 600V, for example).
I really mean it about the CAT rating, to meet that it has to be suitably designed and fused so if you make a mistake (e.g. trying ohms or amps on a live 230V supply) it does not explode in your face. And yes, folks have died that way before
A last final word of caution about multimeters - do not use them to "prove dead" on a circuit you have just isolated. There are so many ways you could make a simple mistake that ends up killing you (e.g. using DC volts instead of AC and seeing very little), so get a simple dedicated voltage tester instead.