Wiring Outlet with 2 Hots

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  #1  
Old 02-14-05, 10:27 AM
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Wiring Outlet with 2 Hots

The outlet in my washroom died and needs to be replaced. There is are 2 hots going to the outlet right now (black & blue are hot and white is the return, so 3 cables total). I wanna make sure I am doing the right thing when re-wiring outlet..
1. Remove tab between the copper side of outlet where hots are installed.
2. Connect hots to top and bottom on that side (copper screw side)
3. Install White on opposite side but do not remove tab.

I would just like to know if that is the proper way to install that outlet?

One more thing, having 2 hots going to an outlet, does that mean that 1 cable is coming from 1 breaker each, thuse 2 breakers are powering top and bottom of that outlet? Thanks for any help.
 
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  #2  
Old 02-14-05, 11:23 AM
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Before I say yes, it sounds like you are assuming that the person who wired this knew what they were doing. Ordinarily, in a multi-wire circuit like your description seems like, the hots are black and red. We are assuming that the black and blue are both hot and the white is neutral. Test each of the black and blue wires one by one against the neutral to make sure they're both hot.

A multi-wire circuit should have two separate single-pole breakers. That is what makes it two separate 120v circuits. If the blue and black are both hot, and are connected to a two-pole breaker, it is really a 240v circuit and wired to the two separate receptacles with a 2-pole breaker is improper. You could tell by removing the panel face and seeing what breaker(s) this group of black/blue/white is connected.

Your description of how to wire this is correct IF you are certain that the black and blue are both hots and are fed from two different breakers.

Hope that helps.

Juice
 
  #3  
Old 02-14-05, 11:50 AM
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slonka,

I second JuiceHead's recommendation: what you want to do with the receptacle is correct, if and only if, the person who did the wiring previously did a correct job, and if this receptacle receives power from two different sources.

I would strongly recommend that you map out this entire circuit before going any further. I'd also ask that you clarify your description here: do you have 3 _conductors_ (wires) feeding the receptacle, or three _cables_ (sets of conductors grouped in a over-all covering)?

If the receptacle is used with a switched half, then both halves could be fed from the _same_ breaker, one half through the switch.

If the receptacle is part of a 'multiwire' circuit, then you have significantly more complexity and more to check. The most important factor in a 'multiwire' circuit is that the two hots be fed from _different_ supply legs. A multiwire circuit _may_ be supplied using two separate single pole breakers, as long as these breakers are on different supply legs. A minor correction to JuiceHead's comment: it is _permissible_ to supply a multi-wire circuit with a double pole breaker, and in fact _required_ if both circuits land on the same device. In your case, if you have a single receptacle with two circuits on it, those circuits _must_ use a double pole breaker.

-Jon
 
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Old 02-14-05, 12:42 PM
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Jon wrote:

If the receptacle is part of a 'multiwire' circuit, then you have significantly more complexity and more to check. The most important factor in a 'multiwire' circuit is that the two hots be fed from _different_ supply legs. A multiwire circuit _may_ be supplied using two separate single pole breakers, as long as these breakers are on different supply legs. A minor correction to JuiceHead's comment: it is _permissible_ to supply a multi-wire circuit with a double pole breaker, and in fact _required_ if both circuits land on the same device. In your case, if you have a single receptacle with two circuits on it, those circuits _must_ use a double pole breaker.


I've always been under the assumption that a multi-wire circuit has to be fed by a double-pole breaker so if one circuit overloads/shorts, both legs trip.

tjz
 
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Old 02-14-05, 01:24 PM
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Nec 2002 210-4(b)

If there's 240 volt potential at the receptacle, then a single-handle 2-pole circuit breaker is required.
 
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Old 02-14-05, 01:44 PM
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A double-pole breaker is always a good idea for any multiwire circuit, but it is only required by code when both hot wires are connected to the same device (which seems to be true here).
 
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Old 02-14-05, 04:39 PM
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And since this is a washroom it needs to be GFCI and 20 amp. If it is a multi wire circuit then you need a double pole GFCI, expensive.
 
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Old 02-14-05, 06:52 PM
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Thank you for your help all....Much appreciated.
 
  #9  
Old 02-15-05, 07:39 AM
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Originally Posted by TomZ1
[I][B]I've always been under the assumption that a multi-wire circuit has to be fed by a double-pole breaker so if one circuit overloads/shorts, both legs trip.tjz
See John's post.

In a GFCI fed multi-wire branch circuit, a 240 volt GFCI breaker has to be used. Even if both hots are NOT landed on the same device. The GFCI neutral will not work on a 120/240 volt GFCI breaker.
 

Last edited by thinman; 02-15-05 at 09:15 AM.
  #10  
Old 02-15-05, 08:06 AM
shreveporteric
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two hots and one neutral

GOt a question, is it a concern that there are two separate hots and only one neutral. If these two hots are fed from different legs at the cb box, isn't there a possibility that up to 40amps could travel back to the box through the single neutral and melt the wire?
 
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Old 02-15-05, 09:17 AM
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Originally Posted by shreveporteric
GOt a question, is it a concern that there are two separate hots and only one neutral. If these two hots are fed from different legs at the cb box, isn't there a possibility that up to 40amps could travel back to the box through the single neutral and melt the wire?
The breakers will trip before the neutral comes close to being burned.
 
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Old 02-15-05, 09:36 AM
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Also, the NEC permits a shared neutral in a multi-wire circuit. That should tell you it is safe, as the Code is a minimum safety requirement first and foremost.

Juice
 
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Old 02-15-05, 09:41 AM
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Originally Posted by shreveporteric
GOt a question, is it a concern that there are two separate hots and only one neutral. If these two hots are fed from different legs at the cb box, isn't there a possibility that up to 40amps could travel back to the box through the single neutral and melt the wire?

So long as the two hots are fed from opposite poles of the breaker box, no...If hot wire 1 has a 15 amp draw, and #2 has a 9 amp draw, the neutral carries 6amps (the difference of the two).

If, however, they are fed from the same pole, then yes, there is a problem...If hot wire 1 has a 15 amp draw, and #2 has a 9 amp draw, the neutral carries 24amps (the sum of the two). Then you have potential for up to 40amps (with 20amp breakers), and a fire.


If a double pole breaker is used, the two hots are on opposite poles. If two single pole breakers are used, you have to be sure they are on opposite poles of the breaker box, and that the application allows two single pole breakers (as mentioned in other posts).
 
  #14  
Old 02-15-05, 10:27 AM
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Building on the previous response.
Remember that the voltage and current are sinusoidal and that the two poles are 180 degrees out of phase with respect to one another. Therefore if you look at the voltage at the instant in time when one pole is at 120 V with respect to the neutral wire the other pole will be at -120V with respect to neutral. Similarly if we add an identical load to each branch the current in each branch is V/R and therefore the current in the hot wire of one branch would be the negative of the current in the hot wire of the other branch. When you add these two currents together to calculate the current in the neutral wire you get zero. Therefore the worst case current in the neutral wire occurs when only one branch is under load.
Scott
 
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