Outlet Question

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  #1  
Old 06-19-07, 01:21 PM
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Outlet Question

Here goes another stupid question...

Why would you ever break off the neutral tab on an outlet? Does it give the outlet more power and why?
 
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  #2  
Old 06-19-07, 01:26 PM
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The neutral tab would be broken off when the top and bottom receptacles are on different circuits.
 
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Old 06-19-07, 01:38 PM
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Can you explain why this matters?
 
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Old 06-19-07, 01:48 PM
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I will try to explain this about the netural tab genrally majorty of the time the resdentail home it is not common to break the netrual tab but hot tab yeah if you have split circuit.


The only very few places we do that if you have two diffrent circuits in one yoke aka the whole repectale

the other place i done that pretty often is the commercal/industrail area have very oddball combation repectales like one repectale is 120 volts on one and second repectale have 240 volts on the same yoke

like this,.
http://www.leviton.com/OA_HTML/ibeCCtpItmDspRte.jsp?item=3393&section=10928

that one example that we used in split circuit [ not too often but it do show up in few spots ]

if need more question please do post it here we will try to help ya

Merci , Marc
 
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Old 06-19-07, 01:49 PM
ddr
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As you probably know, leaving the neutral tab intact but removing the hot tab would allow for one receptacle to be switched while the other remains hot. It would also allow for a multiwire circuit: each receptacle powered by a separate breaker on opposite legs of service but sharing the same neutral. In this situation, the breakers MUST be on opposite legs of service or the neutral could become overloaded since it is serving as neutral to both circuits.

Removing the neutral tab would allow each half of the duplex to be powered by a different breaker, but they would not have to be on different service legs because each would have its own neutral.

In the multiwire setup, since the receptacles are on the same yoke, the breakers would have to be tied together so they trip together. I don't know if this is true if the receptacles are on the same yoke but are fed from isolated breakers with both hot an neutral tabs removed. (I'm sure the pros can answer that one.)
 
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Old 06-19-07, 01:51 PM
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If the neutral and hot tabs are broken off, then each half of the duplex receptacle functions as an independent circuit with its own terminals for hot and neutral conductors. This could be useful where two dedicated circuits are needed in the same location -- perhaps two microwaves on the same countertop.
 
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Old 06-19-07, 01:53 PM
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DDR :;;

see above the answer ., but in commercal / industrail location they useally do that but in resdentail area that kinda very rare.


Merci, Marc
 
  #8  
Old 06-19-07, 02:03 PM
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So basically, you are splitting one circuit into two (at the duplex) by breaking off both tabs.

If I quit making sense since I am so confused, feel free to quit responding. : )

So, if you are using two appliances with the hot tab broken but the neutral connected, since there are two neutral wires, I still don't see why the neutral tab being broken matters since they go to the same neutral bus.
 
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Old 06-19-07, 02:10 PM
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And if the two circuits on the single yoke were the only receptacles on each circuit and it was a 20a circuit in the US you couldn't use a 15a receptacle, Correct? <G>
 
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Old 06-19-07, 02:25 PM
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JFS,

Sometimes two circuits can use the same neutral wire (shared neutral, multiwire circuit), but sometimes the neutral wires cannot be shared. On a shared neutral circuit, you would leave the tab on the receptacle intact. With separate, unshared neutral circuits, the neutral tab would be broken and each receptacle would have its own. Combining neutral wires in the wrong situation will overload the neutral wire(s) and cause a fire. In any case, the need to break the neutral tab in residential wiring is rare.

Ray,

That's correct.
 
  #11  
Old 06-19-07, 02:32 PM
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How about this question. I have one outlet in by bathroom where I currently live. If I went in and broke off the neutral tab, would I be creating a 240V fault problem since the two hots come from the same panel? How can you tell when this is acceptable to do (two hots on opposite service bars?)

Thanks to whoever keeps helping me with this.
 
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Old 06-19-07, 02:41 PM
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Without knowing exactly what wires you have in the box, I can't say for sure what would happen. My best guess is that if you broke the tab, then the top or bottom half of the receptacle would stop working as would any downstream receptacles elsewhere in the house. As I said before, it's rare that anyone would need or want to break a neutral tab in residential wiring.
 
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Old 06-19-07, 02:53 PM
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I'm just being hypothetical here. My basic question is are the two hots in an outlet box in residential wiring always from the same bus? (So breaking the neutral creates the dangerous high voltage fault).
 
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Old 06-19-07, 03:10 PM
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Usually in residential wiring there is only one hot (black) and one neutral (white) source per box and both halves of the duplex receptacle share them in parallel. Don't be confused if there are actually more wires in the box; one set is "incoming" and other sets may be "outgoing" to other receptacles on the circuit. This still is only one circuit chained to multiple locations. This is by far the most common configuration. Breaking either tab in this case would simply cause any receptacles downstream from that tab to not work.

It is rare for there to be two hots in the box, so it's really hard to speculate about that situation. If there are two hots it could be a properly wired multi-wire circuit, an improper or accidental multi-wire circuit created by a careless handyman, or two completely distinct circuits. The outcomes of each case would be widely varied.
 
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Old 06-19-07, 03:24 PM
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Thanks; this is finally making sense. Last question (I think)...if all four wires were still connected to the two hot screws and two neutrals, I can't envision why the other outlets would cease to work if both tabs were broken. The current still has a complete path in the top and bottom half of the receptacle.
 
  #16  
Old 06-19-07, 04:01 PM
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Because the Tabs are the only thing completing the circuit.
Say the "top " pair is coming from the circuit breaker.
The bottom pair is picking up the 'current' via the tabs and continuing on to whatever's downstream. there's nothing internally connecting the top and the bottom - its all in the tabs.
 
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Old 06-19-07, 05:20 PM
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I don't see how what you are describing are outlets in parallel. Shouldn't each outlet be connected to the two lines coming from the breaker...not the previous outlet?
 
  #18  
Old 06-19-07, 06:35 PM
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JFS321,

This is backtracking a bit back to the whole "how does a neutral get overloaded" thing. It's long, but hopefully it will help you understand some of the basics -- I hope it doesn't confuse you more; I’m no pro, but I’ll explain it the best I can (and anyone please correct me if I’m wrong on something).

Let’s take it a step at a time :

Typical U.S. residential service consists of three current carrying wires: two hots and one neutral. The hots “feed” the service panel from a transformer, while the neutral acts as the electricity’s return path to that transformer.

Each hot provides 120V and is attached to one of two “legs” in your service panel, sometimes referred to as leg “A” or leg “B.” Each leg provides 120V. By utilizing both legs, you can run 240V devices.

The electricity is of the alternating current (AC) type which means that, unlike direct current (DC) there is no positive or negative terminal, like a battery would have; current actually goes back and forth (alternating between positive and negative) on the same wire, which is why it is called “alternating” current. Each of the two wires (and therefore the leg it is attached to) is “180º out of phase from the other,” which is a fancy way of saying they are doing the opposite of each other: when leg A is positive, leg B is negative; they then simultaneously reverse and leg A becomes negative and B becomes positive, and so on, constantly alternating. It is important to understand this so as to understand the potential danger of shared neutrals.

The amount of current being pulled is measured in amps (A). If you have 100A service to your home, each leg can handle a maximum of 100A. This amperage does not get “used up” by the devices; if you have a microwave on a dedicated line and it is pulling 10A through the hot wire, 10A is also going back out through the neutral. This is why the term “neutral” is misleading; people often think there is no current because neutral makes many people think of zero.

Electrically speaking, neutral is more of a balance. Because you have two hot wires feeding into your service panel that are 180º out of phase and share a neutral back out, a balance of current is created on the neutral wire.

For example: the same microwave is pulling 10A and is on leg A. A 9A vacuum is running and is on leg B. the neutrals from the two circuits are carrying the full amperage back to the service panel -- 10A from the microwave and 9A from the vacuum. Then, in the service panel, both neutrals meet up at the neutral bus bar. So what happens? Well the logical thing to think is that you would have 19A: 10 + 9 = 19. But what actually happens is that the two amperages are subtractive, not additive. The 9A gets subtracted from the 10A leaving you with 1A going back out the neutral wire to the transformer. Why? Because of the fact that the two legs are 180º out of phase. Since one leg’s power is positive at the same exact moment the other leg’s is negative, the amps being pulled are “out of phase” and therefore cancel (or NEUTRAL-ize) each other. Since there are 9A on leg B canceling out 9A on leg A, all that’s left is the 1A on leg A. This holds true for all current being pulled through the service panel at the same time, so if you have 70A being pulled on leg A and 55A on leg B, 55A are canceled out and 15A goes back through the main neutral. That’s why a properly wired panel can’t overload the neutral, even if leg A was pulling 100A and leg B 0A, only 100A would go out through the neutral; anything turned on on leg B would DECREASE the amperage on the neutral

So what does this have to do with a single circuit and it’s neutral and how can it get overloaded? Well, the setup of the service panel is basically one big multiwire circuit. So the same theory applies to a multiwire circuit run from your panel to a receptacle.

Say you have the top half of a standard duplex receptacle fed by a black wire coming from a breaker on leg A and the bottom half fed by a red wire coming from a breaker on leg B. Both halves share a neutral. Since the top half is fed from leg A and the bottom from leg B, the two halves are 180º out of phase, therefore, just like with the main panel, the neutral from that receptacle will only be carrying the difference in amperage of whatever devices are plugged into the top and bottom:

Say there is a microwave plugged in to the top half and an electric grill plugged into the bottom. The microwave pulls 15A and the grill pulls 15A. If only the grill is on, the neutral is returning the full 15A to the panel. If only the microwave is on, again the neural is returning 15A to the panel. Turn them both on, and the 15A from leg A cancels the 15A from leg B and you have achieved a TRUE neutral -- no current is being returned by the neutral wire. (This is almost never the case except for a 240V device; neutrals virtually always have some current running through them and as such are just as dangerous as a hot wire.)

Now, this is all assuming the circuit is wired correctly and that the breaker for one half of the receptacle is on leg A and the breaker for the other half is on leg B. So what happens if you put both breakers feeding the receptacle on the same leg? Well now the devices are IN PHASE, so the amps don’t subtract anymore, now they add together. Turn the microwave on and the neutral is carrying 15A. Turn on the grill and the 15A from that get added to the 15A from the microwave and now the neutral is carrying 30A, but if the wire is only a 14 gauge rated for 15A, you are exceeding that by 15A and are in danger of starting a fire from the excess heat building up in the neutral.

So:

multiwire circuit (shared neutral) going to receptacle with hot tab removed with hot wires coming from different legs: OK

multiwire circuit (shared neutral) going to receptacle with hot tab removed with hot wires coming from different legs: NOT OK

neutral and hot tabs removed from receptacle with hot wires from either leg with individual neutrals for each: OK

As for parallel vs. series, someone else will fill you in -- my fingers are tired from typing!

Hope all this helps.
 
  #19  
Old 06-19-07, 10:11 PM
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re: tabs and series/parallel wiring

JFS,

Okay, I’m back. I promise to keep this one short(er)...

Regarding your question about tabs and parallel/series wiring:


TABS
The tabs are an essential part of wiring as they are the only electrical connection between the upper and lower receptacles of a duplex receptacle. Once you remove a tab, you are severing the link between the screw terminals and the top and bottom receptacles. Removing the hot tab will sever the hot side only; removing the neutral tab will sever the neutral side only. How it will affect your circuit depends on how it is wired.

SERIES WIRING
The most common way duplex receptacles are wired is in series. The outlets are “daisy-chained” to each other: two incoming wires from panel (first receptacle only) or previous receptacle to top or bottom two terminals of receptacle, then two wires from the other terminals to top or bottom of the next receptacle, and so on, until you reach the end of the run receptacle. Each receptacle has two wires in/two wires out except the end of the run receptacle which will only have two wires in. Note that all wires are connected to the receptacle, therefore the circuit is only complete with the receptacles (and their tabs) in place.

With series wiring, if a fault occurs somewhere, everything from that fault downstream is dead. Everything upstream from the fault will still function. Say you have ten receptacles wired to a breaker. In receptacle 7, the incoming hot wire comes loose. Receptacles 1-6 will still work, but 7-10 will not. If, with the same setup, the outgoing instead of the incoming hot on 7 comes loose, receptacles 1-7 will work, but 8-10 won’t.

In series wiring, removing a tab anywhere in the “chain,” will kill power to anything downstream. Remove the hot tab on 3, and you will lose power to the “outgoing half” of 3 and to all of 4-10 because you’ve cut power to the outgoing half by removing the tab: the electricity has no path to travel through. Remove the neutral tab on 3 instead and you still lose power to the “outgoing half” of 3 and to all of 4-10 because you’ve severed the electricity’s return path: it will now go into 3 and follow it’s only path back: through the incoming part of 3 and back upstream to the panel.

PARALLEL WIRING
Parallel wiring is more work and uses more wire, but avoids certain problems of series wiring. In parallel wiring the incoming and outgoing wires are wire nutted together rather than passing through the receptacle. Two extra wires, one hot and one neutral, are joined at the wire nut junctions and go to the receptacle. This is known as pig tailing. Each parallel wired receptacle has six wires (the end of the run still only has the two incoming wires).

Because the receptacle is pigtailed, a loose connection to it or a removed tab won’t affect anything downstream since the electricity still has a continuous path through the connected incoming and outgoing wires (the connected wires, of course, must be secure or you will still lose power downstream of the loose connection). With this method, you could even remove a receptacle entirely and the rest of the circuit would work fine.

While removing a tab on a pigtailed receptacle won’t affect anything downstream, it will affect the receptacle the tab is removed from. If you remove either the hot or neutral tab, only the half connected to the pigtailed wires will work, the other half will lose power.
 
  #20  
Old 06-20-07, 04:42 AM
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Thanks for the fantastic info. I completely understand what you are saying...I just never knew outlets were sometimes wired in series. I am still a bit confused as to where the neutral legs of each outlet goes to get back to the bus. If electricity is being used in the last outlet on a run, does current flow back through the other ten to the bus? Or does each outlet have a neutral connected separatly to the bus? Thanks again.
 
  #21  
Old 06-20-07, 04:51 AM
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Do not use the terms parallel and series. That will only confuse people. All of your 120 volt wiring is in both series and parallel. In order to get 120 volts at each location, the wiring is electrically in parallel. However, the cable runs serially, from the panel to the first receptacle, to the second receptacle, to the third.

The current on the neutral wire follows the white wire all the way back to the panel, through whatever path that takes.. If you have a cable that runs from the panel to receptacle A, then to receptacle B, then to receptacle C, then the current for something plugged into receptacle C follows the 120 volt (hot) wire from the panel to receptacle A, then to B, then to C, then to the device plugged in. It then follows the neutral wire from receptacle C, to receptacle B, to receptacle A, then to the panel.
 
  #22  
Old 06-20-07, 03:57 PM
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So was the previous statement correct? That if a neutral tab is broken in the outlet "series", that all others downstream do not work?
 
  #23  
Old 06-20-07, 05:00 PM
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Maybe, maybe not. It depends on the connections made.
 
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