In the USA, the homeowner can install or repair their own wiring or switches, fixtures, for major appliances etc, but most don't have the knowledge. Doing the work for someone else home isnt illegal but you should know what your doing of course. Depending on the scope of the job, a city or county permit may have to be pulled at a reasonable cost, then the work is inspected for code violations by an offical covered by the permit fee. New commercial electrical work, almost always, but not always requires a permit, depending on how extensive it is, a permit might be skipped . Commercial repairs do not, generally. Commercial work is always in metal conduit, residential mostly not, depending on the city or county but metal conduit really keeps the electrical house fires down, and most of this commercial work is done by a licensed electrician. But if you own your commercial property and know what your doing, you might skip the permit, but if another trade is working there to complete the buildout and they pull a permit, you could ge fined for not obtaining a permit.