Many of the new ranges,and dryers are now using four wire...

Answer by THG
Submitted on 10/6/2006
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240V is supplied using two hot wires and a neutral wire, with 120V between either hot wire and the neutral. The neutral is connected to ground in the breaker panel. Older 240V appliances used a three-wire feed, with the neutral serving as ground at the appliance; i.e., the metal casing of the appliance was connected to the neutral. Ideally, the load is perfectly balanced, such that the neutral carries little or no current. But a problem arises if the load becomes unbalanced,for example, if a dryer element on one side of the line (between the neutral and one hot wire) burns out or becomes disconnected. In such a case, the neutral can carry a large current, leading to a potential difference between the dryer casing and the ground at the breaker, and also between the dryer casing and the casing of another nearby appliance, such as a water heater, or between the dryer casing and any separately grounded object, such as a metal water pipe. The potential difference can be large enough to be dangerous; for example, if one simultaneously touches the faulty dryer and a water faucet. In a four-wire system, a fourth wire is used for ground and the neutral is not connected to the appliance casing. The appliance casing is connected to the fourth wire, not the neutral. If the load becomes unbalanced, the neutral carries current but the fourth wire does not, so no potential difference is developed between the appliance casing and ground. In a four-wire system, the neutral and the ground wires are connected only in the breaker box. Not at any other place.

Answer by THG
Submitted on 10/6/2006
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PS: You can use three wires by connecting the neutral (usually white) to the ground( usually green), as was essentially done in older, three-wire systems. Doing this can be dangerous, as explained in my previous response. It is better to re-wire the feed using four wires, which involves running a fourth wire from the appliance outlet to the breaker panel, where it is connected to the neutral bar. If that is impractical, and if a GROUNDED water pipe is nearby, go to Home Depot or Lowe's, buy a length of wire and a pipe clamp, and connect the ground wire from the appliance to the pipe. If no grounded pipe is nearby, buy a 10' copper-clad ground rod, drive it almost all the way in the ground by the outside wall nearest the appliance, run a ground wire from the rod to the ground wire on the appliance. Once the appliance is properly grounded, connect the two hot wires and the neutral wire to the three-wire plug.

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Question by Jim
Submitted on 2/15/2004
Related FAQ: N/A
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Many of the new ranges,and dryers are now using four wire plugs.Please explain the reason and can you still wire it with only three wires rather than four?

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