Electrical question

[Brian Shutter]

I'm installing a new ceiling fan with light in my son's bedroom. I think I've got all the wiring figured out but only in my head. One thing that's confusing me is the red wire coming out of the breaker that controls the outlets and switch in his room. From what I can see the black wire from that same romex cable goes to another breaker. How does this work and why is it done like that? Is there anything about this that will affect what I'm doing upstairs?

There is a switched outlet in the bedroom with a red wire that I believe goes from the outlet to the switch (the switch has a black wire going in and a red going out). When the switch is ON, the black is hot and the red is hot (and so is the bottom receptacle on the outlet). When the switch is OFF, the black is still hot and the red is dead (so is the bottom receptacle of the outlet).

My initial thought was that the red wire leaving the breaker was either going directly to the outlet or directly to the switch. But now my assumption is that the red wire coming from the breaker is not related in any way to the red wire coming out of either the switch or the outlet. Does that sound right?

So,

Question #1 Why did the electrician use a 12 or 14/3 on that breaker (as well as on 1 or 2 others)? If the red wire doesn't go to the switch or the outlet, where does it go? Where does the black one go?


Question #2 Since the black wire going to the switch is hot whether or not the switch is ON that must be from the source. How is it then that the breaker with the red wire coming out of it controls the power to that switch?

Question #3 Am I correct in assuming that the red wire from the switch goes to the outlet and nowhere else? It's not hot when the breaker is off nor when the switch is off.


Thanks for your help.

Brian

[Don Baer]

OK I've read your post (4 times) and think that I've figured out your question.

First of all the 14/3 is leaving the breaker box has two hots and a neutral. The red and black are the hots and the white is the neutral. if you were to measure across them you'd get 220 V and from either the red or black to neutral youd get 110V. The black going to the switch is the black from the breaker box. The red from the switch going to the receptical is the switched leg and not the same red that comes from the breaker box. That red hot leg goes somewhere else. Otherwise when you close the switch your have 220 volt short and you blow the breakes and the switch. Hope this makes sense.

[Chris Padilla]

Perhaps not exactly what you have, Brian, but all the room in my house have 14/3 run in them. The red wire in this 14/3 is simply a switched hot...nothing more. Each room has a main feed of 14/2 (or 14/3) to the switch near the door. From there, 14/3 is run to each outlet. I now have the ability to make any outlet switched or even make the top of a duplex outlet always hot and the bottom of the duplext outlet switched. This is a nice convenience I've found throughout my house.

Not to confuse things but I also have 14/3 being run from the house sub-panel so some of the "always hots" are red instead of black but the electrician, once he fed the switch in the room, always made sure that the red became the switched hot within the room.

I hope this has some meaning for you and doesn't confuse things further.

[Rob Russell]

Brian,

You have what's called a "multiwire circuit". That means that 2 hots on opposite phases are sharing the neutral.

Your main panel has 2 hot legs or busses. The 2 breakers the black and red conductors connect to are mounted on both busses - the first breaker on 1 buss, the second breaker on the other buss. The way our panelboards are designed, breakers next to each other are on opposite busses. That's why a 240v breaker is 2-slots wide - so it can attach to both busses.

The 2 hot legs are 180 degrees out of phase. What that means is that, when you have a multiwire circuit where the 2 hot legs are out of phase with each other - much of the current flowing out through each hot leg effectively cancels when it gets to the neutral. That means the neutral conductor only carries back the difference in current between the 2 hots.

Let use some numbers for an example. Assume that your multiwire circuit had 11 amps of current flowing out the red conductor and 12 amps of current flowing out the black conductor. The current flowing back through the neutral wouldn't be 23 amps - it'd be 1 amp (12 - 11).

My guess is that the electrician that wired your house put in some multiwire circuits to save a little bit of money on wire. S/he ran multiwire circuits up to a bedroom with 12/3 or 14/3 and then broke that off into (2) regular circuits. If the breaker with the red conductor kills power to your son's bedroom - what happens when you kill the breaker with the black conductor. It should be marked on your panel and I'll bet it's a different circuit.

In terms of your receptacle - power is being fed to the receptacle for the unswitched outlet. Power then feeds to the switch through the black conductor and the red conductor back to the receptacle is controlled by the wall switch for the switched outlet on the receptacle.

Make sense?

Rob
Addy protocol - unlicensed homeowner electrician

[Brian Shutter]

Thanks guys

Those were the answers I wanted to hear.

Brian