In 1996, the rules about how clothes dryers connect to electric panels changed in many places. Their standard plugs, which used to connect to a three prong outlet as shown in Figure 1, were updated to a four prong version. The earlier models of dryers used to wire the neutral and the ground together, which at the time was accepted by the NEC (National Electric Code) standards. This, however, left the risk of the current flowing to the ground wire and the consequent possibility to energize the dryer’s metal frame, creating the potential of electrical shock.
With the four wire outlet mandated in 1996 (Figure 2), however, the NEC realized that replacing old existing outlets and their wiring could prove to be much too invasive and costly in older homes that would have to be upgraded to the new 4-wire system, and it was decided that the three prong outlets would remain code-compliant.
But when faced with the dilemma of installing a newer dryer and realizing that the plug at the end of the cord and the outlet in the wall don’t actually look alike and seeing there is no way that they’ll fit together (Figure 3), the first thought is replacing the outlet, of course, but since this would include replacing the whole cable, it surely sounds expensive and maybe even impossible if, since the initial install, the basement and other rooms got finished or remodeled, hiding all the electrical behind drywall and ceiling tiles.
But thankfully, the problem is much easier to resolve than it looks. With the three prong 240V outlets still within the code, there is nothing to modify at the outlet. All the modifications are to be done at the dryer level, by first getting a three prong cord from the hardware store, and rewiring it in place in a specific way as described below.
Step 1 - Pick the New Cord
Since the three prong outlet is still compliant with the code, all you need is a new three prong cord that matches the pattern of the outlet. As shown in Figure 4, there are more than just one type of three-prong cords for ranges and dryers, so care must be taken to get the right one.
Step 2 - Remove the Access Panel
After confirming the right cord was picked, the dryer’s electrical access panel is removed to expose the terminal block and connections of its wires. Looking at the four wire cable going in, there are a black, a red, a white, and a green wire hooked up inside as in Figure 5.
It’s easy enough to see on the inside that the green wire from inside the appliance and the green wire from the four wire cord are both secured at the common point on the chassis or case of the appliance connecting everything to the earth ground. The main difference after it’s all hooked up is the green wire from the four wire cord will be missing after it’s replaced with the three wire cord as seen in Figure 6.
Step 3 - Free the Wires
With the proper Phillips screwdriver or socket wrench, remove the screws securing the green wires to the chassis, and the three wires to the terminal block, taking care not to lose any of the screws inside and making note of where each color goes.
Step 4 - Take Out the Four Wire Cable
The cable clamp holding that cord can then be loosened up and the four wire cable can be removed from the dryer.
Step 5 - Insert the New Cord
The new cord (with only three wires) is inserted into the knockout opening that is now freed, but without the cable clamp at this time.
Step 6 - Connect the Wires to the Block
As illustrated in Figure 6, there's no green wire in the new three prong cable, so if the three wires are colored, the wires should be attached to the terminal block to match the same colored wires from the dryer. The “grounding strap” will now replace the green ground wire and can now be connected between the center terminal and the dryer case.
If the new cord is a flat cable without color-coding, the center wire goes to the middle terminal screw and the outside wires go attached to each of the outside terminals on the terminal block. The grounding strap still goes connected as described above.
Step 7 - Secure the System
With the new cable hooked up, the cable clamp can be tightened up to secure the cord in place. With this done, the access cover can also be put back and screwed in place. And there it is, ready to get plugged in and tested.