Steve Firth wrote:

A circuit breaker lockout kit.

Sorry, forgot to mention, if the kit doesn't meet your needs, buy the
components separately:

Safety lockout hasps (select one(s) that meet your needs)

http://www.reecesafety.co.uk/Lockout%20hasps.htm

And padlocks, the best combination is "Padlocks Master & Differ" which
gives you one master key and individual keys for each padlock.

http://www.reecesafety.co.uk/Padlocks.htm

It's probably also worth getting the tags and the training wallchart for
the thickos.