3 wire or 2 wire ?

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  #1  
Old 08-30-02, 04:00 PM
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xfrank12
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3 wire or 2 wire ?

i am replacing BX with ROMEX and adding outlets and switches in an old house.

two of the rooms on the same circut have thier own light fixtures, outlets and switches. but, they share a switch box . duplex switch. i want to get rid of the duplex switch, put a single switch for one room in that box and add a switch for the other room. i also want to add outlets.

they ran 3 wire from the light fixture to the switch then 3 wire from the switch to the other light. outlets in one room are 2 wire from the light fixture and the outlets in the other room are 3 wire from the light fixture. do i need all this 3 wire ? since i am seperating the switches cant i run 2 wire ? do i need 3 wire to the outlets ?
 
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  #2  
Old 08-30-02, 11:32 PM
A
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Wiring:

Sounds as if you have a lot of switched recpt. try making a bit more detailed description of the cicuits, and post back, and i'm sure we can get you through it ok. there will be someone on in the morning that will be great help to you.
 
  #3  
Old 09-03-02, 12:01 AM
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no switched recpt.

although it is hard to tell what i am dealing with because the old BX has lost most of its color codeing, i can tell that most of the BX in one room is 3 wire and it appears one of the
3 is not used. they didnt use wire nuts, they twisted the wires together and taped them, then folded them over and taped them again. some wires are taped to other wires. i think they taped unused wires to the rest of the wires.

would it be safe to assume they either did not know what they were doing, they had a lot of 3 wire lying around so they used it everywhere, or that someone remodeled and no longer needed the 3 wire ?

if i take out all of the BX, run 2 wire to the first light fixture, 3 wire to the second light fixture, 3 wire to both switches and 2 wire to the outlets, i will be all set right ?

my first post was because i was wondering if there was a reason for all that 3 wire, now i am thinking i should just take it all out and start over.
 
  #4  
Old 09-03-02, 07:48 AM
J
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The first 3-wire cable is likely needed so that power can be supplied to the switch box, and switched power can be returned. You didn't say, but it seems that the power supply comes into the first light. The original wiring needed to send unswitched hot and neutral to the box, and get switched hot back. This cannot be a switch loop, because power must then be supplied to the other light.

The reason for the second 3-wire is less clear.

The unusual and dangerous method of connections should raise red flags big time. Be suspicious of everything you see, and be very careful. Removing everything and starting over is an excellent idea, assuming you know everything you need to do it correctly this time.
 
  #5  
Old 09-05-02, 11:47 AM
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xfrank12
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i have removed all the old BX. i was correct, 3 wire everywhere, but only the black and white were used , except for between the fixtures and switch, where the red wire was used.

now, let me know if i have this right.

power comes into the first room at an outlet. i will run 2 wire from that outlet to the light fixture.
3 wire from that light fixture to the second light fixture in the other room.
3 wire from the second light fixture to the switch for the second light fixture.
3 wire from that switch back to the switch for the first light fixture in the first room.
then 2 wire to the outlets.

i want two seperate lights on two seperate switches in two seperate rooms.
since the two lights are only 20 feet apart, i think this is the easy way.

finally, just for the sake of arguement, do i have to use 3 wire ? isnt 3 wire only used in this configuration because it is easier then running more 2 wire ?
 
  #6  
Old 09-05-02, 12:15 PM
J
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There are many ways to make this work, but the way you have presented is not one of them. I think you should do some further study before starting this project. Read a book or two on home wiring. It appears that you do not sufficiently understand the principles of electricity.

If power comes into an outlet in the first room, here's the simplest way that will work, and it uses no 3-wire cable. Use all 2-wire cable (plus ground). Run a cable from that outlet to the switch in the same room. Run a cable between the two switches. Run cables from each switch to the light that the switch controls.
 
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Old 09-05-02, 03:50 PM
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i thought this newsgroup was FOR people who didnt sufficiently understand the principles of electricity.

those two lights worked for seventy years with 3 wire.

i just checked a room that i know a real electrician wired in the 1960's. he used 3 wire between the switch and the light. he retired with out loseing his license.

according to " better homes and gardens step by step wiring ", they use 3 wire between the fixtures, 3 wire between the second fixture and the first switch and 3 wire between the first switch and the second switch.

i realize if i was only adding one light and one switch, two wire is the way to go. but , i thought in my configuration, 3 wire was easier.
i guess myself, better homes and gardens and that electrician from the 1960's were wrong.
 
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Old 09-05-02, 08:27 PM
J
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Yes indeed, this forum is for people who need some help understanding. And I'm happy to answer any and all questions you ask. But realistically, I can't write a book here. And that's exactly why I suggested a real book. It will add a lot to your understanding that can't all be covered easily in a question and answer format.

There's no magical difference between 2 and 3 wire cables. The cables don't really make any difference -- it's the wires that make a difference. You need to get an uninterrupted neutral wire to every light and receptacle. You need to get an unswitched hot to every unswitched receptacle, and a switched hot to every light and switched receptacle. Finally, you need to get a grounding wire to everything. There are nearly infinite possibilities in the routing of cables, and the number of wires in each, that fulfill these basic requirements.

You only need to use a 3-wire cable if you need 3 insulated wires. There are a number of common reasons you need three insulated wires. Here are some of them: (1) 3 wires are needed for certain 240-volt circuits, such as ranges and clothes dryers. (2) 3 wires are usually needed when using 3-way and 4-way switches, since you need two traveller wires plus a neutral in a cable between switches. (3) 3 wires are needed in split-wired receptacles, where you have two hot wires on opposite phases and one shared neutral wire. (4) 3 wires are needed for a switch loop when you want to use one wire to return switched power, while using another wire to carry unswitched power on from the switch. (5) 3 wires are needed when you have two switches in a box controlling separate fixtures, such as a ceiling fan with a light or a bathroom with a light and an exhaust fan.

The point is that you should only use a 3-wire cable when you know that you actually need 3 wires. You need to think not only about the wires, but about the connections at each end. There's no point running 3 wires if you only have two things to connect them to at the end.

Before running any cable, think about the way each wire will be connected to the switch, receptacle, light, and/or another wire at each box. Draw out a circuit diagram. Label each wire as to its purpose, e.g., neutral, switched hot, unswitched hot, traveller, etc. For simplicity, omit the bare grounding wires when drawing the diagram -- they are implied. Make sure that you can trace one hot and one neutral from each light and receptacle back to the source of the power, without such wire being in series with any other receptacle or light.
 
  #9  
Old 09-08-02, 10:37 PM
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jumping in here...

John you mentioned a bunch of reasons to use 3-wire. I'm fairly new to this stuff (but reading voraciously!).

My understanding that another valid reason to run 3-wire (plus gnd) conductor is for a series of small appliance GFCI kitchen outlets- the 3-wire lets you alternate circuits between outlets. Is this correct (I hope so, since i'm doing it). the last outlet would get 2 conductor.

I'd love some feedback!

Thanks for your detailed posting, by the way - I got a lot out of it.

Tony
 
  #10  
Old 09-09-02, 06:38 AM
J
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3-wire cable for small appliance circuits in the kitchen in the U.S. is a terrible idea (see my response to your other post). It is okay to run 3-wire from the panel to the first box in the kitchen, but you must then split the 12/3 into two 12/2s, or you must use a GFCI receptacle in every box (i.e., no downstream protection).

Multiwire circuits are fine if you fully understand all the strange details, but should be avoided by most DIYers.
 
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