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 4x15mph 11-23-2008 02:53 PM

Neutral Wire?

I want to add in some dimming switches that require a load, line, ground, and neutral (?). I pulled out the current switch and there are only 3 wires connected to the switch;ground, load, line. I do see 2 white wires in the back of the gang box and they are capped off. Is this the neutral wire and do I just join a third "jumper wire" to that pair for purposes of feeding a neutral to my new switch?

Thank you!

 jerryh3 11-23-2008 03:00 PM

Most likely they are the neutrals. If you have a voltage tester, measure the voltage between the whites and the line wire. It should be 120V.

 Nestor_Kelebay 11-23-2008 04:42 PM

4X25MPH !

The 220 volt wiring going to your house will have a total of 4 wires in it:

1. A black wire that carries 110 volts,

2. A red wire that also carries 110 volts. The difference between the black and red wire is that they are 180 degrees out of phase, so that when the black wire is at +110 volts, the red wire will be at -110 volts and vice versa. The 220 volt appliances in your house, like your stove and electric dryer will have the heating elements connected between the black and red wires so that there would be a total of 220 VAC across those heating elements.

3. A white neutral wire. Think of the electricity coming into your house along the red and black wires and leaving along the white wire. If all the appliances in your house were pure resistors, like light bulbs, toasters, electric heaters and electric frying pans, then theoretically, both the voltage and current sine waves in the red and black wires would perfectly cancel each other out when the met at the white wire, so that there would be no voltage and no current in that white wire.

However, in practice many of the appliances in your house have "impedance" and that means that the inductors and capacitors inside the appliance cause the voltage and current in the black wire (and also in the red wire) to go out of synch so that the current isn't at a maximum when the voltage is at a maximum and vice versa. Your clothes dryer, for example, has an electric motor in it, which acts like an inductor or "coil" of wire, and the interference of the magnetic fields around each wire in the coil interfere with the current flow in all of the other wires in the coil, and that causes the current sine wave to lag behind the voltage sine wave in the wire coming out of the motor. Similarily, your TV set and computer monitor have huge capacitors in them, and in a capacitor the current is at a maximum when the voltage is CHANGING most rapidly, so that causes the current to be at a maximum when the voltage sine wave is at it's maximum slope at ZERO volts. Thus, that causes the current sine wave to be out of phase with the voltage sine wave in the wire coming out of your TV set or computer monitor.

Because of these "impedances", when the out of synch voltage and current sine waves from the black and red wire meet at the white wire, they most often won't cancel each other out perfectly, and you can actually get fairly high voltages in that white wire, like 40 volts or more.

4. The ground wire, which is always green or has no insulation at all.

Most of the electrical circuits in your house are 110 VAC circuits. Some of them are driven by the red wire, and some of them are driven by the black wire. The current from both kinds of circuits go back to the generating station along the white wire (or it's easiest to think of it that way). The ONLY circuits that will be connected between the black and red wires will be the 220 volt circuits to the 220 volt appliances, like stoves, electric dryers and electric water heaters. But, even the cables going to these appliances will need a neutral white wire inside that cable. That's because within stoves and electric dryers there are also 110 volt circuits, such as the one that powers the electric motor in the dryer and the ones that power the indicator lamps and convenience outlets on electric stoves.

The reason why the white wires are connected together in your electrical box is because the power is coming in through EITHER a red or black wire, going through the switch and then continuing through a red OR black wire to the light fixture and then back through the white wire to the generating station. That's why the white wires are connected together in the back of your electrical box.

If you have something like a light in the dimmer switch you're installing, then current has to flow through that light to the white wire in order to get back to the generating station. So, you would connect the white wire on the back of your dimmer switch to the white wires already connected together inside your electrical box. That is, connect all three white wires together.

I wrote up a blurb about basic house wiring for a lady who wanted to know how the new electric dryer she bought should be connected. If you want to know more about your house's electrical wiring, I can see if I still have it saved somewhere and I can post it in here for you.

 jerryh3 11-23-2008 04:56 PM

Quote:
 Originally Posted by Nestor_Kelebay (Post 189145) 4X25MPH ! The 220 volt wiring going to your house will have a total of 4 wires in it: 1. A black wire that carries 110 volts, 2. A red wire that also carries 110 volts...
Does the wire have to be red? Both ungroundeds coming into my house are black. Also my nuetral(grounded) is stranded aluminum. Should I be concerned?

 4x15mph 11-23-2008 07:48 PM

Thanks for the feedback

So, should I add in another 'jumper' wire to the other white wires and connect this to my switch or is there another method?

How do I check to see if the white is neutral? Will it read -120v if I use a votage meter? Do I set the voltage meeter on ground and the neutral wire?

Thank you

 jerryh3 11-23-2008 08:10 PM

Yes, add the pigtail from the other neutrals. The meter should read 120V between the line and the neutral.

 Nestor_Kelebay 11-23-2008 08:42 PM

Jerry:

No, the actual colours of the main power lines coming into your house aren't important. What's important for a home owner to realize is that there are two power 110 volt power lines coming into their home, and these are 180 degrees out of phase. Each voltage source can be used individually to create 110 volt circuits for lights and electrical outlets in the house, or together to create 220 volt circuit for the 220 volt appliances in the house. It's just that they differentiate between different voltage sources by using red insulation on the wiring for one voltage source and black insulation on the wiring for the other voltage source.

I can't speak much about the grounding of panels. I have a small apartment block, and my main panel is designed in such a way that you can't even open it without shutting off power to the whole building. I did check my parking lot sub-panel (that provides power to 14 cars in winter) and the white wires are NOT grounded. I think you should talk to an electrician to see if main panels are grounded differently than sub-panels. That's something I wouldn't know.

 Nestor_Kelebay 11-23-2008 08:57 PM

4X15mph:

Quote:
 I want to add in some dimming switches that require a load, line, ground, and neutral (?).
The "line" connection is where the voltage source wire (the red or black one from the panel) connects to your dimmer switch. The "load" connection is where the wire from the light you're controlling with the dimmer switch connects to that dimmer switch. You now have to add a white neutral wire from the neutral connection to the other two white wires. That's called a "pigtail".

Quote:
 How do I check to see if the white is neutral? Will it read -120v if I use a votage meter? Do I set the voltage meeter on ground and the neutral wire?
If you use a volt meter between the neutral wire and a power line, you will read 120 volts. And, that's true regardless of whether you measure between a red and white or between a black and white wire. It doesn't make sense to say +120 volts or -120 volts because it's alternating current and 1/120th of a second from now those voltages will have reversed. Your meter will just read 120 volts in both cases.

If you read 120 volts between a black or red wire and a white wire, then it's safe enough to presume that the white wire is 0 volts and the red or black wire is 120 volts. To confirm, simply measure the voltage between the white and ground, and you should read a low voltage, perhaps no voltage at all.

 4x15mph 11-24-2008 01:00 PM

Thank you everyone. Great info and I have what i need

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