A NEMA 6-15 plug has two horizontally-aligned straight-blade prongs and one horseshoe-shaped prong. A 6-15 plug's prong shape and spacing only fits into a NEMA 6-15 receptacle. The horseshoe-shaped prong pushes into the receptacle's ground terminal and the 6-15's horizontal prongs slide into the receptacle's hot slots. A NEMA 6-15 plug is for a 250-volt, 2-pole circuit with a ground. It's what you use to supply electricity to some window-mounted air conditioners and commercial office equipment.
A Word about Cable
Normally, when you wire a 240-volt circuit, you use 10-gauge or heavier 3-conductor wire, but a circuit controlled by a NEMA 6-15 is different. The recommended wire gauge is 14, and the plug has no neutral terminal, so you don't need 3-conductor cable. Do yourself a favor and use 2-conductor 12-gauge wire instead.. The thicker cable is insurance against overheating and fires. Make sure to wrap black or red tape around the white wire inside the plug and at the circuit breaker to indicate that it's a hot wire and not a neutral.
Wiring the NEMA 6-15 Plug
Remove the last 3/8 inch of the insulation from the end of each wire entering the NEMA 6-15 plug with wire strippers. Some wire sets use three insulated wires — usually black, white and green colored — and some use two insulated wires — usually white and black colored — with an additional uninsulated wire. Don't forget to identify the white wire as hot.
Grip the middle of the stripped portion of each wire with a pair of pliers. Form the end of the wire into a hook shape. Loosen the three NEMA 6-15 plug's wire terminal screws with a Phillips screwdriver. A NEMA 6-15 plug uses a green screw and the letter "G," found stamped into the plug's body, to identify the ground terminal. The two unlabeled wire terminals are brass and connect to the live wires.
Slip the ground wire's hook over the NEMA 6-15 plug's ground terminal screw, then tighten the terminal screw. The ground wire, the green or uninsulated wire, protects the appliance's user from accidental electrocution. Connect one of the hot wires to one of the NEMA 6-15 plug's hot terminal screws -- it doesn't matter which one -- then .tighten the terminal screw. Connect the remaining wire to the other terminal in the same way.
Finish Up the Job Safely
After you've made the wire connections, double check to make sure no exposed wires are touching inside the plug, then slide the plug casing together and tighten the screws to hold it. The plug should have a cable clap attached to it. Tighten this clamp down, then give the plug a good tug to make sure it's secure before plugging it in to the 6-15 receptacle.