3 wire versus 4 wire


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Old 07-16-07, 03:36 PM
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3 wire versus 4 wire

I am curious when and why the code change was made concerning 3 wire verses 4 wire when wiring dryer and range.I know the present code calls for 4 wire but a customer asked why and when the change was made.
 
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Old 07-16-07, 03:49 PM
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I'm not an electrician, so you can take whatever I have to say to a grain of rice.

Code is probably requiring that a dryer receptacle to be 120/240 volts instead of just 240.

120/240v require to have the neutral, red, black and ground.

240v requires only black, white(hot), and ground.

I could be wrong.
 
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Old 07-16-07, 03:56 PM
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The older 3-wire is still 120/240V, but is UNgrounded, with the case of the dryer bonded to the neutral.
 
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Old 07-16-07, 04:00 PM
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^^ ----

This is why I'm not an electrician.
 
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Old 07-16-07, 04:06 PM
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To keep the neutral/ground circuit separated from each other, because with the old 3-wire system, 120 volt power will run through the metal body of the machine, to ground, via the neutral wire.

But, by having it's own true ground, in the case of the newer 4-wire system, only in instances of a short could current flow through the body of the machine.

When you hook up an appliance to the 4 wire system, you want to disconnect the jumper terminal at the appliance's block terminal, that bridges the neutral and ground. And hook up the two power legs and neutral to the correct block terminals and the green ground wire to the case of the machine where designated. Then the neutral and ground are independent of each other.
 
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Old 07-16-07, 04:58 PM
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you are all correct;

the hazard of a open neutral connection causing a shock is the reason. In no other wiring arrangement, can a open connection directly cause a shock.
 
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Old 07-16-07, 06:29 PM
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Had a friend call because the refrigerator was zapping her when she touched it. Refrigerator was next to stove. Only happened when she was touching something on the stove while opening the refrigerator. Yes, you guessed, open neutral on a three wire stove connection. The refrigerator was a modern one with a grounded plug. Basically she was acting as a path for the stoves neutral.
 
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Old 07-16-07, 07:24 PM
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The change was made in 1996. Folklore has it that the code allowed 3-wire during WW2 to save copper for the war. I have no idea why it took them until 1996 to switch. It should have been obvious long before that that the safety improvement of 4-wire was well worth the extra wire.
 
 

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