All of the above is excellent advise. To add to this I would have to say that ones knowledge of electricity and understanding of the current National Electric Code (NEC) is a must. In addition to that you need to know and understand the local codes that applie for your location which can be differant then NEC's requirements. If you do electrical work for profit, charge people, most municipalities say you must be licensed and bonded and registered to do work in that city. Some places allow you to do electrical work if the service is free to a person (friend) provided it passes an inspection.
To answer your question, when should you call an electrician... When you don't fully understand how something should and will work before you start, if you don't understand how to make the necessary tests to make the job safe for you and/or people around you and if you don't know what the codes are for what you are trying to do. If you can't answer YES to the above 3 items please call an electrician so you can come back here and post some more. ;D
ALSO Please call an electrician if...
you use Penney's in your fuse box
you staple extention cords to the wall
you use high wattage light bulbs for additional heat
you use masking tape to insulate wires
you have to tape your circuit breaker in the on postion
you blow dry your hair while soaking in the tub
your color blind
you claim your blindness on your income tax return
your friends call you Sparky
you think bonding a box means gluing it
you had straight hair before you started wiring and now its curly
your light comes on before you flip the switch
you think finding the hot wire means touching it
you have pee'ed on an electric fence 1 or more times
The staff in the emergency room call you by your first name "Hi Sparky"
and the list goes on... :D
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