It is very easy to understand why many people get confused when attempting to install an electric dryer. For starters, the heavy cable used on an electric dryer may have three or four heavy wires. Since 2000, electrical code states that four wires are required. For many people fooling with these heavy wires is very intimidating. The wires are heavy gauge because the dryer heating element draws 15 Amps. Normal lamp cord wiring will get hot and melt. I have seen many novices cause a lot of trouble by mixing heavy and light gauges. Most folks are frightened away by the heavy wires and leave the job to appliance technicians or electricians.
Many different situations are encountered. If a person moves an old dryer to a new house they may be faced with an old three-prong line cord on the dryer and a four-prong outlet.
Second, a new dryer does not come with a line cord. Often a retailer will sell the customer a four-prong cord (The current code). When they get home, they find that their house has a three-prong outlet and they don’t know what to do. Of course, they are irritated because they thought all they had to do was plug it in and start drying clothes. I must admit that fewer and fewer homeowners attempt to connect up anything involving 220 V. It scares them to death. However, this post will explain the logic behind the national code changes and how to handle these situations.
First, let’s review a bit of history. When electric dryers first came out 60-70 years ago they were all hardwired to the house (no cords were made back then). The cable used was 10-3 with the ground. It included four wires. Three of the wires were 10 gauge a black, white and red. The fourth wire was 12 gauge, bare copper.
The three colored wires were attached to the terminal block on the back of the dryer with the white wire going to the center. The bare copper wire was screwed to the metal frame or shell or the dryer. The red and black are interchangeable but typically the red is connected to the right-hand side of the block. Nothing could be simpler. It was hard to get it wrong. The white wire and the bare ground wire parallel one another back to the panel box and are connected together and to the earth. The neutral wire carries minimal current while the red and black carry the heater circuit. The bare ground wire carries no current and it’s purely a safety circuit.
As the years went by new homes were built with a dryer outlet already installed in the wall and three-prong line cords were made available to connect the dryer to the heavy outlet. These line cords were three wire only and did not include the bare wire.
A cautious electrician or homeowner would add a bare wire, a ground wire, from the case of the dryer to the metal case of the outlet or a water pipe. This insured that the metal case of the dryer was directly connected to the earth ground through the electrical system of the house. By doing so it was impossible to get a shock by touching the dryer.
A grounding strap was added next to the terminal block inside the dryer connecting the center tab (the white one) to the chassis metal of the dryer. This was the second way of ensuring that the metal case was connected to earth because the white center wire is connected to the earth back at the panel box. All of these shenanigans are in place to prevent or dissipate any voltage from appearing on the case of the dryer thus preventing electrocution.
With the advent of the extra-safe four-wire heavy line cord the missing bare ground wire from decades gone by has reappeared within the line cord. It is the fourth wire and color-coded green. This green wire is to be connected to the chassis or case of the dryer. The grounding strap within the dryer (supplied by the manufacturer) is removed. The new green wire takes it place.
Back at the panel box the green wires, any bare copper wires, the white center neutral wire are all connected together and directly connected to the utility ground and also to a heavy copper rod that is driven into the earth.
Back to the problem at hand, it is far easier to change the line cord then it is to change the socket.
Consequently, match your line cord prongs to the socket holes and by a line cord that fits.
Wire the matching cord as shown here.
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2 Replies to “How to Wire a Three or Four Wire Dryer Outlet”
Can a 220 circuit function safely with no separate neutral. In other words, with 2 110’s and a ground?
Each of your 110VAC circuits already has a neutral wire. However it’s more complicated than that as what you are are doing is not code nor safe. You must be connected to a 220VAC breaker to get both sides of the incoming 220VAC to the house. Get an electrician!