You can splice low voltage wires with solder and electrical tape or with various connectors or splicing kits. Choose your connecting method depending on the type of cable, the voltage and the current. For ordinary household wiring, electricians use twist-on connectors secured with electrical tape and placed inside connecting boxes. Shrink tubing gives a neater and more long-lasting result than electrical tape. Low voltage, underground wiring requires special treatment as does high current wiring. Silicone sealer seals such wiring against water infiltration.
Get twist-on wire connectors for ordinary household wiring splices. Turn off the power. Install a connecting box or use an existing box. Insert the cables through the connecting box holes. Strip one inch of insulation off the wires to be connected and twist the wires with matching colour of insulation together. Twist on the twist-on wire connectors. Wrap the connectors and connected wires with electrical tape. Place the connected wires in the connecting box and tighten the strain-relief clamps on the cables. Screw on the connecting box lid.
Use solder and shrink tubing for low voltage wiring such as 12-volt indoor wiring. Disconnect the power. Slip a three-inch length of shrink tubing over one wire of each splice. Strip one inch of insulation off each wire. Twist the wires of the same polarity together horizontally and smoothly so that the twisted portion is in line with the wiring. Solder the connection so that the solder penetrates the twisted wires. Slide the shrink tubing over the splice. Blow on the shrink tubing with a hair dryer until it has shrunk over the splice.
Use a splice kit to join low-voltage outdoor wiring, such as landscape lighting. Disconnect the power. Strip one inch of insulation off each wire and place the wires into the connector supplied with the kit. Twist or close the connectors as per the kit's instructions. Insert the connection into the protective tube and seal the tube as per the instructions which came with the kit. Bury the sealed, waterproof connection.
Connect special wiring with high currents or wiring subject to stresses using a kit which gives extra strength and protection. Turn off the power. Strip one inch or more of insulation off each wire as required by the kit. Place the wires into the connectors and crimp or tighten the connectors as described in the kit's instructions. Place the connection into the protective sleeve or container and heat-shrink or tighten it as per the kit's instructions.