# Purpose of neutral wire?



## LeakingFaucet (May 12, 2014)

I am replacing a Panasonic FV-WCCS1-W WhisperControl Three-Function On/Off Switch that recently stopped working. I intended to use a Leviton single pole light switch but noticed it lacked a neutral wire.

Here's what I think I know:
Red wire - positive voltage
Black wire - negative voltage, 180 degrees out of phase with red wire
Green wire - ground, grounded via some conductor dug into the foundation in my house

What is the purpose of the neutral wire?


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## nealtw (May 12, 2014)

Start over: the single pole has black in and black out, with white tied together in the box

The other switch has black to the light and red to the fan or the other way around


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## beachguy005 (May 12, 2014)

Forget what you think you know.  Are those the colors of the leads on the switch?
What is the color and how many are the wires coming into the switch box?


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## LeakingFaucet (May 12, 2014)

The Panasonic switch comes with 4 wires. 3 are soldered to the PCB inside the switch, 1 is screwed to the metal plate which screws to the junction box.

3 soldered wires:
Red - Live, understand what this does.
Black - Live, understand what this does.
White - Labeled as neutral. What does this guy do?

1 screwed wire:
Green - Ground, understand what this does.


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## slownsteady (May 12, 2014)

I can understand if you don't want to pay $$$$ for an exact replacement, but are you willing to give up the extra features of the Panasonic switch?

http://www2.panasonic.com/webapp/wc...556669&catGroupId=193042&surfModel=FV-WCCS1-W 

A single pole switch is simply not the same thing. But if you just want to turn the fan on or off manually, you should wire the new switch just like a light switch. 

Does the power source go to the fan first, or directly to the switch that you're replacing?


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## JoeD (May 12, 2014)

Neutral goes to neutral. The dimmer PCB needs to be powered so it needs a hot and a neutral wire.


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## nealtw (May 12, 2014)

It should go to the other two white wires that are in the box.


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## kok328 (May 12, 2014)

I installed a Leviton Occ Sensor a while back and it came in two different models (w/ & w/o neutral connection).
The neutral most likely pigtails off the neutral in that circuit.

However, if your installing a regular light switch, then just cap it off with a wire nut.


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## Wuzzat? (May 12, 2014)

LeakingFaucet said:


> What is the purpose of the neutral wire?


*Nominally* it provides a return path for the current that is supplied by the 'hot' lead.  But since it's AC, the roles of the 'neutral' and 'hot' conductors are *actually* exchanged 60 times per second (in the US).

It's something like a 110v to 120v volt battery connected to two wires and the battery polarity is switched 60 times/second.

However - the neutral, being grounded at the panel, should never have a voltage more than two or three volts at the distant end when measured with respect to earth ground.


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## beachguy005 (May 12, 2014)

If you're looking to replace that control with a single pole switch, it doesn't matter what wires it comes with.  You need to determine if you can wire in a sp switch with the existing feed.

As for the neutral, it does the same thing as a ground wire.


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## Wuzzat? (May 12, 2014)

beachguy005 said:


> As for the neutral, it does the same thing as a ground wire.



Nah, c'mon. . .


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## beachguy005 (May 12, 2014)

I meant that they both run back to the same spot in the panel.


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## nealtw (May 12, 2014)

beachguy005 said:


> I meant that they both run back to the same spot in the panel.



As it is a true statement, it may not be a good idea to say when someone without expireince is wiring a switch:2cents:


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## LeakingFaucet (May 13, 2014)

Thanks, Wuzzat?, you're the only guy to answer my question.

I thought all current flowed from the higher voltage to lower voltage lines (red and black) as the voltage oscillates. I thought the ground wire would draw any current that might not transfer to the lower voltage line. In that case, is the neutral wire unnecessary?

For anyone else, I have connected the neutral wire in my switch the neutral line.


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## Wuzzat? (May 13, 2014)

Thanks, Wuzzat?, you're the only guy to answer my question.
>That's because I am educated way beyond my intelligence. . .

I thought all current flowed from the higher voltage to lower voltage lines (red and black) as the voltage oscillates. 
>If you have a 0.26 ohm resistance (about 100' of #14 copper) with 10A flowing eastward, the west end will be 2.6v higher, more positive, than the east end.


I thought the ground wire would draw any current that might not transfer to the lower voltage line. In that case, is the neutral wire unnecessary?
>With no fault present, the ground conductor may carry microamps, depending on what's plugged in at the distant end of the cable.  The neutral carries the return current which is a much higher current.

>If the appliance fails and some of the current goes to the ground conductor which is probably connected to the appliance's metal case, this conductor will keep the voltage on the case of the appliance very low when measured with respect to earth ground.  
If the current in the ground gets high enough the breaker will trip.   

>You could run the appliance off the hot and ground wires but that's not the purpose of the ground lead.


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## nealtw (May 13, 2014)

LeakingFaucet said:


> Thanks, Wuzzat?, you're the only guy to answer my question.
> 
> I thought all current flowed from the higher voltage to lower voltage lines (red and black) as the voltage oscillates. I thought the ground wire would draw any current that might not transfer to the lower voltage line. In that case, is the neutral wire unnecessary?
> 
> For anyone else, I have connected the neutral wire in my switch the neutral line.



You are looking at this wrong.
Power comes from the breaker on the black wire to the switch and the black to the fan and then back to the breaker box on the white.
The only reason you have a red wire is because you have a light and a fan and you need to switch them both.

So you have black from the breaker to the two switch black and red from the switch goes to the fan and light. The fan and the light each have a white wire that goes back to the breaker box.

This auto switch also needs a white to make it work but that isn't the normal for most switches.


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## LeakingFaucet (May 13, 2014)

nealtw said:


> You are looking at this wrong.
> Power comes from the breaker on the black wire to the switch and the black to the fan and then back to the breaker box on the white.
> The only reason you have a red wire is because you have a light and a fan and you need to switch them both.
> 
> ...



This Panasonic switch is for the Panasonic condensation fan that does not have a light. The button on the front is to manually activate the condensation fan.


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## LeakingFaucet (May 13, 2014)

Wuzzat? said:


> With no fault present, the ground conductor may carry microamps, depending on what's plugged in at the distant end of the cable.  The neutral carries the return current which is a much higher current.



So is there fancy internals in the switch that choose where to run the current? Out on the ground line vs the neutral line?

Any reason other appliances don't require such a fancy switch?


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## slownsteady (May 14, 2014)

I think it's the names that are confusing you. "Neutral" is not neutral in the sense of being unused or unimportant. Back when I was a kid, it was called "Negative" - probably because electricity is explained to kids by using a simple DC circuit. The white (neutral) wire completes the circuit back to the service panel. The "ground wire" is a safety line in case the there is a short circuit in the normal path. It drains the power from the parts you may touch or that may get too hot in your wall. A 3-wire cable (black, white, red...plus ground) is usually just a convenience  so you don't have to run extra single wires in cases where it is required.

The Panasonic switch has a lot going on inside that probably requires a second path  to the fan (this is a whole house fan or attic fan that we're talking about, right??).


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## LeakingFaucet (May 14, 2014)

slownsteady said:


> The Panasonic switch has a lot going on inside that probably requires a second path  to the fan (this is a whole house fan or attic fan that we're talking about, right??).



Nope, this is a bathroom fan. It's the matching sensor for their bathroom fan.


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## slownsteady (May 14, 2014)

ahh, makes sense. I wasn't sure what the humidity sensor was all about. have you checked to see if there is anything in the area of the installation that would be giving the switch trouble? Maybe it gets too hot where it is or something like that.


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## Wuzzat? (May 14, 2014)

So is there fancy internals in the switch that choose where to run the current? Out on the ground line vs the neutral line?
>AFAIK no switch or appliance runs more than microamps into the ground line.  It's probably a violation of some U.L. rule.

Any reason other appliances don't require such a fancy switch?
>It depends on how much they are asking the switch to do.  
Running extra wires is so costly and electronics nowadays is so cheap that they can squeeze quite a bit of performance from one, two or three wires.  Or they just go wireless.


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## JoeD (May 14, 2014)

Normal switches do not run any power out a ground wire. A ground is NOT a current carrying conductor.


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## Wuzzat? (May 15, 2014)

Actually, increasing current in the ground wire could indicate that the appliance insulation is breaking down and over 5 mA should trip any GFCIs in the line.
For a few dollars in parts you could make a tester that will not blow out the internal fuse on your multimeter's current measuring ranges.


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