Replies

1. 
   Coolflow_ | Nov 17, 2000 05:37am | #1

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   It's code, so the neutral path will not be opened if the device is removed. Why is this important? If there was a multiwire receptacle downstream sharing the open neutral and there was something plugged into each outlet they would be essentially connected in series with 240 volts across them. If they were really unbalanced loads one would see a lot higher voltage across it than the other

1. 
   Ralph_Wicklund | Nov 17, 2000 06:03am | #2

   *I didn't really understand your question but that won't stop me from answering.If you are seeing 3-wire, terminating at a single duplex outlet, then you may have a split outlet where (usually) the black wire is an unswitched hot and is wired to one half of the outlet and the red wire is a switched hot wired to the other half. A small metal jumper tab is cut on the hot side of the outlet to separate the two. The neutral (white) is attached to a screw on the other side of the outlet and the jumper is not cut.Pigtails are used in parallel wiring where a particular box not only has an outlet but is a passthrough to other outlets. A pigtail (a separate length of wire) is attached with wirenuts to each side of the circuit and then to the outlet. In the above 3-wire example if that box is also a pass through then the white and the black wires should have a pigtail. When the outlet is used as part of the circuit (all four side screws have a wire) the little jumpers pass the power through and no wire nuts are used. Attaching all four wires to the outlet is wiring in series. You'll find the series connections made in many of the older installations and quite often the wires are cut too short to manipulate. A real pain when changing outlets. Grounds are also pigtailed when in a passthrough as well as being looped to a ground screw if a metal box.Clear as mud??And what Rick G said, too. Except I don't follow the 240 volt ref.

1. 
   RJT_ | Nov 17, 2000 11:27pm | #3

   *Thanks Rick and Ralph. I did not do a good job of describing this circuit so I will try again. In the case of a kitchen where one would want to have a string of outlets that alternate between two circuits. The first choice would be to run two 2 wire plus ground to every other outlet each wire. In that circuit the white wire goes into one side of the outlet and out the other to downstream outlets. The other alternative would be to run one 3-wire plus ground with the red (hot) to the first outlet, skipping the second outlet to which the black (hot) would be wired. To each outlet however the white wire is pigtailed to the outlet and to the circuits downstream. Rick: I follow the device disconnect thing, but not the 220/240 possibility. Come again?Thanks.

1. 
   G.LaLonde | Nov 18, 2000 12:33am | #4

   *RJT, You sound like the kind of guy that should be hiring an electrician to do this work !! When using a three wire circuit, you must have the hots on opposite legs of your service entry or you will fry your common neutral. What Rick was trying to tell you is what could happen if the neutral circuit is broken or interrupted in some way. This is the same thing that happens when the neutral is corroded in your main service somewhere. Three wire circuits used to be a common way to hook up kitchen receptacles to save running two cables, but with the requirement for GFCI circuits in the kitchen ,and cheap wire ,this is not usually done anymore. I would suggest you run the two separate circuits if you understand how to do that properly.

1. 
   lonecat | Nov 18, 2000 02:01am | #5

   *And pigtail the receptacles anyway, don't just feed thru em.

2. 
   RJT_ | Nov 19, 2000 06:31am | #6

   *G.LaL: good advice, I'm not going to use this type of circuit as I do not understand it well enough, and actually would cost more.

3. 
   John_Sprung | Nov 20, 2000 11:26pm | #7

   *OK, about the 120/240 thing: The power company's transformer on the pole has a center tap secondary. That center tap is grounded at your service entrance, and connected to your neutral buss. Between neutral and either of your hots, you should find the nominal 120 volts. Between the two hots, you should find 240 volts. If you run neutral and both hots to a place where you put a receptace on each hot and use the neutral for both receptacles, what happens is that the neutral carries the difference in the current between the heavier and lighter load. Say you have a 100 watt bulb on one side, and a 60 watt bulb on the other. The hots see their respective loads, but to the neutral, it looks like 40 watts. If that neutral becomes disconnected, you now have the 100 watt bulb and the 60 watt bulb in series across 240 volts. The total voltage across both bulbs is still 240, but because the connection between them is floating, they don't share that voltage equally. Current is the same in both bulbs (at least for a fraction of a second), but the 60 has a higher resistance and the 100 lower, so the 60 gets, from Ohm's law, a higher voltage, and burns out.Now, according to Murphy's law, the lighter load will always consist of the more expensive devices, such as computers, stereo equipment, TV sets, etc.... ;-)-- J.S.

4. 
   RJT_ | Nov 21, 2000 03:09am | #8

   *I've got about 5 books on electrical wiring, I generally go thru them, then I ask questions here on anything I don't understand, and finally I ask three different electricians that I know personally. I advise that anyone follow the same routine. As an example of a scenario for disaster: one "basic" book I've got does not specify that the hots for a 3-wire circuit should be switched together to prevent the possibility of switching one circuit off and leaving the other on. Although I still do not plan on using this circuit, I would like to understand it. Here is what I do not understand: if each outlet has only a red hot or a black hot, if the neutral is gone from the first outlet and the next outlet has a black but no neutral outlet back to the source.... oh, wait a minute I think I'm starting to get it, I'm going to have to diagram this out for myself and will get back later on this.

2. 
   RJT_ | Nov 21, 2000 03:09am | #9

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   ......how come the white wire is pigtailed to the outlet whereas in a single circuit (two wire plus ground) you feed into the outlet and out the other side?