Indoors or outside, always use CSA approved lights. Check each set of lights, new or old, for broken or cracked sockets, frayed or bare wires, or loose connections, and throw out damaged sets.
Use no more than 3 standard-size sets of lights per single extension cord.
Never use electric lights on a metallic tree. The tree can become charged with electricity from faulty lights and a person touching a branch could be electrocuted.
Fasten outdoor lights securely to trees, house walls, or other firm supports to protect the lights from wind damage. Use only insulated staples, not nails or tacks, to hold strings in place. Or, run strings of lights through hooks (available at hardware stores).
Turn off all lights when you go to bed or leave the house. The lights could short out and start a fire.
For added electric-shock protection, plug outdoor electric lights and decorations into circuits protected by ground fault circuit interrupters (GFCIs). Portable outdoor GFCIs can be purchased where electrical supplies are sold. GFCIs can be installed permanently to household circuits by a qualified electrician.