What can a self-employed qualified electrician specialise in?
Seriously, if you are the self employed qualified electrician, you better learn your field more if you don’t know what category to specialize in. As a business owner, and not an electrician, my only suggestion would be go into the commercial field. You will be less likely to chase your money from businesses than private owners. The odds are that less business checks bounce or do not pay than private party funds.