What Do Electrical Wire Color Codes Mean?

Leave a Comment - 97


kevin jackson

Subject: Wiring cooktop

I have a 4 burner electric cooktop that has a red a black and ground. Coming from the electrical panel is a red, black and white. How should these be connected? 240v

T. Buck

Subject: Furnace problem

Put a new furnace in about 5 years ago. It started having problems. Codes didn't help and finally called a tech. He did some thing on it and it worked until his warrant ran out. Problem again, I bought a new board and it worked. Problem again, new board. It start acting up recently and I found if I turned the breaker off and on it would work maybe for two days then go to the breaker again. Would the main ground wire from the fuse box being not as tight as it should be cause this problem?


Subject: Ceiling light

Ceiling box has three cables coming out white blackout ground wires. Ceiling light has 1 white 1 black and ground I know black hot wire goes to fixture black not sure about white wire and other two cables


Subject: Wiring a light fixture from one switch

With only a white and black wire coming from the electrical box for the fixture. We attach the bare wire to the box and leave it long enough to be attached to the light fixture bare wire. Or the bare can be attached to the box so it bonds the light fixture. Now the white wire is the neutral and is only attached to the white wire of the fixture . Leaves the black or switched hot to be attached to the black wire of the fixture. \if the fixture has more than one white, join them all together with the white wire from the box and so with all the black wires. Pinch all the same color wires with one hand then with your pliers give all the stripped a twist. Should be 1/2 bare or so then if need be trim all to the same length and apply a wire nut tight. Pull on the connection to make sure it is connecting all the same wires then repeat for the other color wires. Good practice is to wrap a small amount of tape around and up over the wire nut. put in a bulb and test before screwing the fixture to the box. Good luck


Subject: swag ceiling fan

I have an old swag ceiling fan, that has the chain you hang from ceiling connects to a 2 prong cord. There is a green wire from the bracket on the ceiling. Coming in from the fan (that was already put together) is the 2 prong wire split... there is a black/white wire, black, white, green. When I hung the fan, I had the black/white, and white connected to the 2 prong wire that was split. The light worked but fan did not. I went to Home Depot told me to connect the green on fan to green on bracket (as the ground). But I still have a black wire coming up from fan. Not sure where it goes?


Subject: Swag attached ceiling fan wiring

This wiring confuses lots so don't be sad. You have to think like you are hooking up two devices. One the light and two the fan. So some people have the fan wired to a switch on the wall and the light on a separate switch. Nice but putting in a fan where there was only a light is ok you just use the pull cords on the fixture. Ok so the green is attached to the green and on to the junction box as the bond or same as the bare wire. Then the fan will be the white/black, the light will be the black and the white only is the neutral. Hook the black and the white/ black with the black from the junction box . Then the white to the white. Now when you turn on your wall switch you are applying power to the black and the black/white so now can control the fan and light on the fixture pull cords. Hope this helps.


Subject: fan wiring

Don't ask Home Depot. An hour ago I was talking to someone about a switch issue. He said the White is the hot. I don't know much, but I know the Black is the hot, and White is neutral.


Subject: which wire do I use where

I am trying to put a new isolator switch on my boiler. I have 8 wires. Cable 1 earth.grey.blue.black. cable 2 has earth brown black and blue. Which do I put where. I am confused. Switch has 2 sets of L1 and L2 and two neutrals. Please help I'm without hearing with two small children. Thanks.

anthony simonowicz

Subject: wire confusion

I opened up a light switch and has a red 2 Black 2 white and a ground how do I hook them up to a new Switch on the back to install the two lights are connected together but not connected to anything with a black electrical tape around them


Subject: Cap the whites ( neutral)

Cap the whites ( neutral) together. Lead black (hot) on top of switch screw, secondary black and red on the on the bottom


Subject: Colors are standardized and cross generations.

I was a programmer and web designer that took time off and got into the oil/gas burner business. My mentor had utterly no concept of positive negative and ground. There are no "color codes" in his 77 years of wiring 200 year old houses.

In oil burner relay switches, you have a black and white wire. If there is a green wire, it's screwed into the junction box. The orange is the motor, the violet is the ignition, etc. My 77 year-old boss ties the white wires to the junction box at the point of the relay. For me, that's a complete misunderstanding of ground v.s. negative. Worse, we're dealing with things that could destroy a city block if we get it wrong.

Your article needs to be expanded. Orange may be a motor and violet may be an igniter (standard). If my apprentice ass gets it wrong under a 77 year old, we may both be responsible for blowing up a city block.


Subject: Black & White wires to low voltage?

An outdoor post light broke and I found one that looks exactly the same so it matches the others. The wires on the new one are black and white with a copper ground. But the wiring coming out of the post is low voltage (two wires conjoined, all black). Can I connect this light to low voltage wiring if I use a low voltage light bulb?


Subject: Charging Cable

Okay, so I want to switch an 11 pin charging port to a 5 pin charging port. I did it by switching the wires, but there is a problem. I don't know which wires to connect with each other. For one cable I have a red, orange, white and a sky blue kind of colored wire. And for the other one I have a red, black, white and green wires. Can I connect these together?


Subject: garage door sensor replacement

The wiring for the garage is red and one white. The wiring on the sensor are different the the old sensor. One is white and the other one is white with a black stripe. What do I hook together


Subject: The N would go to your white

The N would go to your white which are neutral wires, and the red would go to the L wire, because they are "hot." Generally the red is wired to a switch. If it was black it would be independent of a switch.


Subject: wire connection

i have a cord that has black,red,yellow and green for my coach recliner sofa,how to connect those wire? there's only three connector on it

Guillermo Gutierrez

Subject: miswired light switch?

I have been in my house for about two years and finally got around to checking the light switch in my daughter's room that appears to not work. one cable has a red and black wire going into the switch the other has just the black wire going into the switch. the white wires on both are connected to each other. could this be why it doesnt appear to work any of the outlets in the room? how should it be wired and do I need a different type of electrical switch?

Paul Tag

Subject: 3 year old home wiring

I live in Illinois. I'm trying to put in a regular double light switch for my outside and inside garage lights, instead of my automatic one that went bad. But I only have one Black wire coming from the wall for the two light switches. I have a bunch to choose from coming from the wall: 2 White, One Yellow, one Blue, One Bright Orange (not red for sure) and of course, one Green. My 2 standard light switches only have 2 screws to connect to on just the one side, with 1 Green for neutral. What goes where? Thanks!

mantis lum

Subject: central smoke detectors

I have a central smoke detectors in the house. There are three smoke detectors on three different floors, the basement, main and second floor. The wires from the ceiling are all black, white and red. The smoke detector on the second floor has all the wires red, black and whites connected together, but I found that both on main and in the basement the white wires were disconnected, I'm not too sure if the main and basement wires both got disconnected from the nut by accident from pulling on the wires. Do I have to reconntect the white wires back on to wire together or do i leave them apart? Thank you


Subject: Installing new electric cook top

Have lines from the wall = white, red, black and from cook top= red, black and green. Do I connect red to red, black to black, cap the white and connect the green to the junction box?


Subject: Confusing wiring colors

I'm installing a Home Depot ceiling fan. I'm confused because I only have 3 colored of wire. Grey, white, and bare copper. The issue is the grey and white are connected to get her with wire nuts and the grounds are all tigether. My new fan has a white wire , black wire and a green wire. I know the green goes with the bare copper, but how do I pick which grey and white pair from the ceiling do I connect the to the fans black wire or white wire to which grey and white?

Tom the ToolMan

Subject: Confusing colors

Get a multimeter and set it to AC and connect one lead to the bare copper (ground) and then, with the power ON, one at a time, touch the other lead to the white wire then the grey wire. One of these should read nothing (this is your neutral), and one should read 110v (this is your hot or live wire). If this is not the case then call an electrician because you have an improperly wired circuit. Next turn OFF power to the circuit, and connect the green fan wire to the copper, next connect the white fan wire to the neutral, and lastly the black to the OFF live wire. Finish hanging your fan and turn ON the power, all done.


Subject: Oven

I am replacing an old oven,. The new oven has Red, Green, Black. The source has Red, Green, Black, and White. Do I cap the white and connect the others color to color? I tried this and it seemed to work but I am hesitant to close it all up until I am sure it is right.


Subject: Toy Wires

I'm doing a school project, and I need to know what colors wires mean in toys. Need it within 6 days!

Girly Girl

Subject: 4-H DPA Project

Hi. I am on fifth grade and I am doin DPA for 4-H. I did electricle wiring and I need simple definitions for the black wire, white wire, and bare wire.


Subject: Thermostat wire

I have a thermostat that has letters for from top to bottom R W Y I have only 2 wires coming from the wall, a red and yellow, there is also a green stuck into the wall not utilized when I hook the r to r and y to y the furnace continues to run any ideas?


Subject: I'm guessing these are

I'm guessing these are probably low voltage thermostat wires that come from the heater, and not from a power source. You need two wires to complete a circuit - voltage and a return path. The red and yellow wires provide the circuit loop that is needed to provide low voltage power for the thermostat to operate.

Keane Oshita

Subject: porch and garage lights

I'm replacing the porch and garage lights. The wires coming out of the house are red, white and yellow. The wires on the fixture are white, black and bare copper. I know the copper is the ground. How do the others connect? I assume it has something to do with a three way switch? Is one of the wires coming out of the house a ground?


Subject: Extension cord colors

I read everything above with great interest. However, my situation seems different. I am putting a new female and on an extension cord, and it has white black and grey insulation on the three inter wires. Black should be hot, but both gray and white are neutral? Which is ground?


Subject: Extension cord colors

What you are describing is totally – well, largely – nonstandard. Use the black wire for hot (brass screw), white wire for neutral (silver screw), and the gray wire for ground (green screw). I'm assuming here that the gray wire is supposed to be green, and since all three colors are to be hidden from the user the manufacturer felt free to use whatever they had in stock. Ground is supposed to be either a green-coated wire or an uncoated wire.

If you have a continuity tester, use it to make sure that what's hot, neutral, and ground on the male end is still hot, neutral, and ground on the female end.


Subject: Wireing help

My wire has four wires a black wich I know is hot a white which is nuteral and a green and also a bare copper wat is the green for if the bare copper is ground


Subject: GFI circuit breaker

I have an outside electric receptacle controlled by, I believe, a GFI circuit breaker. The CB appeared to not be working because I could not read 120v at it nor get continuity through it. It also would not reset.

I replaced the CB and it trips normally when test is pressed. However, once reset there is no power to the receptacle nor other recepticals also controlled, again I believe, by that CB. Could I have the blact"hot"wire and the white neutral wires to the CB reversed causing the circuit to have no power?


Subject: Ceiling fan question

Hooking up a ceiling fan. Instructions say to connect red from fan to black from the box, then white to white. Problem is I have a red wire coming from the switch box also. It is capped. Do I follow the instructions or go red to red?


Subject: 3-way light switch -- wire colors?

Trying to replace a 3-way pull switch.

Old switch only had white and black - matched up easily to the group of black wires (for lights) and the white.

New switch has Blue and Red along with black.

What goes where?


Subject: Wires with Clear Casing

Trying to replace my kitchen light. The pendant light I bought has two clear wires. Neither one has anything different about them, and they are not marked. I read that one could be ribbed, but it's not. Both smooth and both hooked up the same way to the bulb base. No difference whatsoever. If I take a chance and reverse the wires, will it just not work, or will it cause a fire?? Please help.

Andrew Spear

Subject: Two clear wires

Does the pendant light have a replaceable bulb? Is the bulb a 110VAC to 130VAC-rated bulb? (versus a 12Volt DC bulb) If so, it is important from a safety viewpoint how the wires are to be connected. One of your clear wires should be connected to the center tab inside the bulb socket. That will be the hot or load wire. It will carry the voltage to the bulb. At the other end it will connect to a black wire. The insulation should be smooth on the outside opposite the other wire.

The other clear wire should have a small rib running parallel to the wires on the outside of the insulation on the side away from the other wire. Look and feel it carefully. One of the wires' insulation MUST be marked with a color difference or the ribbing. This rib marks the groundED or neutral wire to the circuit. (notice, I did not say groundING. Grounding wires are bare or have green insulation. They are the safety wires in the electrical system). The neutral wire should be connected to a white wire in the box. At the bulb end it will connect to the outer shell of the socket. It is important from a safety viewpoint because if you should happen to touch the threaded part of the bulb while you are screwing it in or taking it out, you do NOT want it to have any voltage on it.

If you still can not identify which wire is the grounded or neutral wire, use a continuity checker, meter, or other device to determine which wire is connected to the outer shell of the bulb socket. If you don't have one of these, take the pendant to a friend or back to the store where you bought it and ask them to help you identify which wire is the neutral wire.

Hope this helps.

Mike G

Subject: White/Yellow/Orange Wire Colors

I am trying to install a ceiling light fixture and the wire colors in the box are white, orange, and yellow. There are no black or green wires. What should I hook up to each of these color wires?


Subject: 220v

Sounds like that is a 220v gangbox. Not a safe place to be poking around in if you don't know electric code.


Subject: White, orange and yellow wires?

If these are the colors of your house wiring, you have two options.
1) purchase a voltmeter, hope the white is neutral and connect the negative lead of the voltmeter to it then test the other two while the circuit is hot to determine which is positive (usually black)
2) Call an electrician unless you are adventurous and well insulated. I've been shocked more times than I care to think about and I can safely say, if you have any kind of metal tool in one hand and a hot wire in the other, the chances of survival are proportionate to how many witnesses you have to remove you from being "the circuit". Even if you only wind up paying someone just to come out and LABEL the wires, it's money well spent. Ignorance is NOT bliss!

Vince D'Amico

Subject: Yellow wire to ?

I just ran some 14/3 guage wire to a fan/light in a bedroom since it had originally been some old 2 wire black & white. But am confused about the multi-fan-light switch (with no schematic) I had in the garage.
On this switch, it has a black wire that I wired to the Hot black which goes back to the circuit breaker & to the black wire going to the ceiling. A red wire that I capped to the red going to the fan motor? A green wire capped to green to ground. I then capped all the neutral white wires together from the circuit breaker, the new wire to the ceiling & the switch. And finally a yellow wire... have no idea?


Subject: I have three white wires, a

I have three white wires, a red wire and the three dark gray wires (clipped together by a copper box) coming from the ceiling outlet box. Obviously the white wires go together, but where do I attach the black wire and bare ground wire from my new light fixture?


Subject: ceiling box

Generally there will be a grounding screw in the box, a green screw, or if there are other bare grounding wires they can be wire nutted together. The black wire will be your HOT wire, and your whites are NEUTRAL, depending on your switch setup, you can wire nut the blacks together with an extra piece of wire coming from the wire nut to connect the hot to the light, as well as the same method with your white wires.


Subject: Wire connection confusion

I'm installing an ventilation fan eith light in my bathroom. Two wires are coming down from my ceiling. One blue and one white. My installation instructions tell me to connect the vent wires (black and white) to a black switch box wire. The light wires ( blue and white) are to be connected with a red wire. Since I don't have a red or black switch box wire, I'm not sure what to do. Help!

Arthur. Gooch

Subject: Vent

Your blue connects to black that's either your switch leg or constant hot disconnect!!!!! Power and check with a hot stick!!!


Subject: Getting shocked at light switch

Have a commercial building, light switch box is metal with metal conduit, light is high output fluorescent in a walkin cooler. When I turn on the light switch and happen to touch a nearby toaster I get shocked. When the switch is off no problem. I took a meter and went from toaster case to switch box and when on showed about 5 volts maybe, when I turn the switch on, apx. 115 VOLTS! any ideas what's wrong? Had a local electrician look at it today and he was puzzled and said will have to think on it and get back to me???

Arthur. Gooch

Subject: Switch

It's grounded out some where check to see if any hot wire has been skinned could be faulty switch or light wire may need to be repulled


Subject: wires colors : black-yellow-green

I have to install the electrical supply for a chiller (230V, 60Hz). The wires of the chiller are black, yellow and green. The green is the ground but which one is the live , black or yellow?

Thank you for the help.

Uthpala Hettiarachchi

Subject: wiring in an old plug point

In my house, there is a plug point which has 3 wires - one green and two black ones. I want to replace the plug point as it is broken....... I know that the green one is the earth wire but I don't know which one is the live wire and which is the neutral one because both are black..... Please help me.... Thanks in advance........


Subject: simple

Since you are probably talking about a plug in your wall which is 220-240V AC. Alternating Current means that plus and minus continuasly alter between the two other wires so there really is no difference.


Subject: Wiring

There is a black 1 whites a red and a blue for a range hood. What is the blue and red


Subject: Wires

Red is your hot. Blue is also used to carry a power source as well.


Subject: Old 4ft x 2ft light

I'm trying to hook up a old light I got and there are 4 wires coming out of it. The are white black green and red and its 120 volt. What I'm connecting to only has 3 wires that are black white and green. What do I hook the red wire to?


Subject: Your wires

Well white is your neutral green is your ground and black and red are your hots. Wrap the black and red together. Then hook up the black and red to your other black wire to your fan connect your other wires as coded. Easy peasy.

Diane Cannuli

Subject: Farsisa intercom-doorbell connecting wires

I'm not sure how I should wire this. The intercom has 4 wires: green, black, red, and white. The power source has only two connector screws, with no indications as to where to put what wire. Do I put the ground wire with the red wire? Does the neutral go with black? I don't want to blow up anything! Help.


Subject: old wireing in a home. white and black wired togeather?

Trying to wire the lights in a bathroom ceiling light and vanity light with double light switch. Two wires going into the vanity light B/W and B/W.
Two wires going into the light switch B/W and B/W.
In the vanity light a white wire is tied to a black wire together those two wires goes to a single white wire at the light switch.
The vanity light a black wire goes to the black wire at the light switch.
In the vanity light a white wire goes to the light switch to the black and white wire tide together.
How do I connect the wires correctly to the double switch?


Subject: Color coding

In a control circuit red is 120vac, blue is DC and yellow is a power source coming from another panel.


Subject: 2 wires

We have pulled out a cupboard and found red and black wire out of the wall. Would like to put a light up but the fittings on the light requires 3. Can it be put up with 2 or should we cover up the wires?

D. Wilson

Subject: touch lamp replacement sensor

This is a question....i sent for a touch lamp sensor..when i compared new to old new was way smaller box & wires im wondering should the wires themselves match in size? I feel theyshould..


Subject: Which is ground?

I have a cord that has brown, blue, and white with a green line. which is the ground


Subject: ceiling fan wiring confusion

In the midst of a ceiling fan replacement and have come across a wiring issue. House was built in 2006 and located in TN. The new fan is a mid-level Home Depot type with a lighting element. The issue is that the fan has red, white, and green wires only. However there are red, white, black, and copper (ground) coming out of the ceiling. Any ideas what I should do to rectify this situation? Can two of the house wires be connected to one of the fan wires? Thank you!

AJ Chilson

Subject: Fan wiring

Your house is set up for a fan with a light on it.(black wire) The fan you purchased seems to have no light.(no black wire) Wire your fan red-red, white-white, green-ground, and cap the black wire. Try the switch after you wire it up. If the fan doesn't come on, first make sure you have power, then wire the red to the black and cap the red.


Subject: Cf

Buy a voltage tester. (Hot stick, wiggy) that will light up when you touch the insulation on the wire. Either the red or black is controlled by the switch. Turn switch on and off why testing to be sure which is which. Cap (put a wire nut on) the one that is not controlled by switch and use the one that is.


Subject: wiring

I have a two switch outlet on seperate circuits (one foyer and one coach lights). I want to place a timer on the coach lights. the old timer switch outlet wires had one pigtailed black and red, one white and a single black. The timer has a black (hot), white (load) and green (ground). I connected the timers hot (black) to the outlet hot (black/red) and the load (white) to the white and the green to the single black assuming it is a ground (note: this single black did not light up my meter when checked with the nuteral (white) so assuming it was a ground (not hot). Am I wiring this correctly? I did get power to the switch but it would quickly turn on/off and then after I waited a bit (switch has a load delay) it would do the same thing.

Aaron Bartholome

Subject: Old wiring

I'm replacing a ceiling fan/light kit, and the existing wiring is red/brown/green. The new fixture is white/black/green. Am I correct in assuming that red goes to black and brown to white?


Subject: No

I do not believe that is correct. Green obviously goes to green because that is your grounding wire. Red goes to black or black to red because those are your hot wires. Although a white wire should only ever be connected to another white or grey wire. White and grey wires are your neutral wires and those should never be connected to brown which is a hot wire.


Subject: Extension cord

I have an 3 wire 15A 125V extention cord that had both the plug in and the recepticle bad.
I purchased two new ends with the proper three prongs, 1 male and 1 female.
My question is where do the white, black, and green wires hook up.

Thanks You!


Subject: as I learned from my first

as I learned from my first mechanic, easy to remember... black wire to brass screw (B+B), white wire to silver screw (or neutral to nickel , nickel being silver, N+N) and ground to green screw (G+G)


Subject: And this all depends on

And this all depends on people installing the wiring correctly - I've lived in a house where half the wiring was reversed, and the white was the hot.

Gus Linja

Subject: Electrical

Many years ago when I was working as an electrician with a carpenter. He had his own motto about electrical work; "I know everything I need to know about electrical wiring and that is hands off" He was an Excellent Carpenter but never claimed to know or wanted to do electrical work.

steven warren

Subject: very confusing because years

very confusing because years ago there were basically no standards and people were being electocuted on a regular basis.national electrical code changed that in home wiring black is always hot and white is always neutral green is always ground and red is half of a 220 volt circuit. any thing else is wired wrong and neededs to be repaired. by a quafified electrician.


Subject: heavy duty extension

my heavy duty extension cord consists of 3 rubbers outer wires, but the inside of them are not colored.
How do you know which one is ground?

Gerry Gaydos

Subject: Wire colour coding

It should be noted at the outset that these comments pertain to architectural and AC appliance wiring, not automotive (DC 12 volt) wiring, in which red and brown are always hot, black is ground and various other colours are used to help visually separate circuits. Black is always a (-) ground.

lenney ott



Rod Bosley

Subject: wire color

you are incorrect. Black, Red & Blue are used on voltages up to 250v, all signify they are current carrying conductors. Neutral would be white, ground wires are either green or green with a yellow tracer.
Brown, Orange and Yellow are all current carrying conductors used on voltages up to 480v.; gray is the neutral color, grounds are green and green w/ yellow tracer.

The purpose of color coding is to standardize & identify the voltages available within the panel/junction box. Most commercial building use 208v and 480v. Residential is wired at 120/240v

Some Guy

Subject: wire color

Rod, all wires are "current carrying conductors". Even green and green/yel carry leakage current and sometimes full current to perform their safety functions.

This article is rife with incorrect information, which could be dangerous to anyone who tries to rely on it. Wire color coding is very specific to the particular device/industry. While there are some standards, they only apply in some types of circuits. Black is not always hot. In DC circuits it is normally grounded. Sometimes it is normal to connect a white wire to a black wire in an AC circuit (switched circuits, for example). Untrained people should not mess with residential AC wiring.

Alan W. Tannous

Subject: wire color coding

The purpose of color coding wires is to properly identify the conductors designated for specific purposes. This will lessen the possibility of connecting or terminating conductrors improperly which may result in a variety of dangerous situations. For instance only the white conductor should be connected to the white screw or white wire on a receptacle or lighting fixture. Will the device normally continue to work if the white and black conductors are reversed? The answer is yes, but with potentially disasterous results. How will this happen, well for instance, all devices with a switch will turn off the power (Hot) supply to that device. If the wires are reversed, then the switch is opening and closing the neutral conductor and the device is still energized.

Dr. Ed

Subject: Purpose of Red, Yellow, & Blue in 120 Volt Single Phase wiring

Short version -- the guy doing the wiring isn't clairvoyant and the next guy working on it is neither clairvoyant nor the one who actually did the initial wiring -- and there is a real need to know -- at both ends of a wire -- that it the same *one* wire. Before computers and glass fiber, the telephone company had thick black cables with 128 wires inside -- they only needed two for each telephone conversation, but it had to be the *same* two from Maine to California. So first, they made it into 64 pairs of two wires each (there were other advantages) and then using 6 colors and having a second color for the second wire (e.g. white & orange, white & blue, red & green) they could have a means of identifying each of the 64 pairs of wire.

Think in terms of 64 very long extension cords all connected to different things a thousand miles away, and you have to know which *one* extension cord to plug in, with bad things happening were you to mistakenly plug in any of the wrong 63. The only reason the wire's insulation is colored is so that you can distinguish between them. And hence the black hot, white neutral which dates back to the days of "knob & tube" - exposed 1/4" copper wires on porcelain insulators - where you could clearly see where each wire went. You could see the hot wire going into the switch (this one *always* hot) and you could see the wire coming out that was only hot when the switch was turned on. Both are "hot" wires, but if you confuse the first for the second, or somehow connect the two together, the switch won't do anything -- nothing will happen when you turn the switch "off" because it has been bypassed.

So you use a red wire coming out of the switch -- you know that the black one is *always* hot, and the red one is *sometimes* hot (i.e. when switched "on") and you connect the red (and not black) to your light fixture, connect the white to the other side of that, and, like magic, you have a light you can control with the wall switch. (CAVEAT: Always presume red is *always* hot unless you know otherwise, it's used for other things too.) And this is why you use sometimes use yellow for the wire from the switch to the light fixture -- you may already have red in the same conduit and don't want to confuse the two. Hence yellow being the wire coming from the switch, used ONLY for the lights that switch controls. After all, there may be reasons why the hot wire going *to* the switch is red instead of black, and were you to use two red wires on the switch, you'd have the same issues if you were using two black ones.

Now say you want to have a switch at the top and bottom of the staircase so that you can turn the light on/off from either end -- a "3-way switch." Instead of the on/off switch, these are switches that are either/or -- there are two wires between them and the light goes on when both switches are connected to the *same one* -- and it doesn't matter which one is used, but each switch is hot and the light goes on when electricity can come in via one switch, go through either wire to the other switch, and then to the light. Otherwise, it is off. You need to distinguish the wires that connect the two switches from (a) the always hot, (b) the hot-when-on feeding the light, and (c) the neutral (and green ground if applicable). Hence the use of yellow and sometimes blue, and it gets a bit more complicated when you have a *4*-way switch -- any one of *three* switches able to turn a light on or off.

Now this is assuming that whoever did the initial wiring was following the rules (think of the person that doesn't stop for the red light and the problems that can cause) -- and that everyone who has worked on it since then did likewise. If you see Aluminum wire (silver rather than copper-colored metal under the insulation), presume otherwise. While still used for big wires (e.g. the feed to the breaker box), the short version it that was used for the 15/20 amp circuits for a couple years in the 1970s until people realized (a) that it was more brittle than copper, (b) that it was breaking, and (c) it was causing fires. It often breaks inside a wall, and then whatever it was connected to stops working -- and people doing a good job simply yank it all out and replace with new copper wire. Or you get creative, and I once found the *ground* (not neutral) being used as the hot, with the outlet then grounded directly to the baseboard radiator -- it worked fine until the tenant tried to use an air conditioner....

The most important thing about wire color is not will something work if you get it wrong -- it usually will -- but what will happen if the next person presumes you did it the way you were supposed to -- and you didn't. Think of driving down the road, through a green light -- you are presuming that the 100,000 lb truck will stop for the red light and hence not sideswipe you.

B Dole


black is used for power in all circuits?
What about automotive circuits?

Dr. Ed

Subject: Auto circuits

Excepting redundant grounds and things like the wire connecting the engine to the frame, ALL auto wires are hot. (The metal frame is used as the ground - which is why any bare wire will short out. With the exception of Orange and Yellow, which are reserved for airbags and high-voltage lines in hybrid/electric cars -- do not touch these -- automakers use whatever colors they please, and then what they do is put a stripe of a different color down the wire to further distinguish them. E.g. green with blue stripe.

You need the wiring diagram of the specific car -- and often there will be wires not used in this particular car because they have the same wiring harness for lots of different cars. Manufacturers tend to have similar colors used for similar things, but you should not rely on that.

W.L. Barton

Subject: The color codes stated in the

The color codes stated in the article refer to A.C.wiring. Cars use D.C. and it's a whole different color code with the exception of green as ground. In D.C., red is hot (positive) and black is ground (negative). If your question (and answer) is to help you diagnose a problem with your car, buy a meter. Also, your public library probably has an online data service that will let you obtain wiring diagrams for your car which include wire colors for each circuit (as well as other repair information). All you need is a library card.

View Comments - 97 Hide Comments

Post New Comment

Offers <
Popular <
Answers <



This can be maddening. Over the past 40+ years, in 4 houses, I have had or have run across this problem from gas meter leakage, water well pump column vibration, doorbell transformer, circulating pump, an extremely small (mist spray) water pipe leak, flourescent and sodium lights, security system horn dead battery, gas meter leaking slightly, bees in wall, bat colony, electric typewriter left on, stereo left on very low, and speaker inductive hum.

This seems to be a popular and recurrent question, so I am going to give the long answer for use by future questioners too.

I am assuming you do not hear this noise away from your house, or that other family members can hear it to. Obviously, if you hear it elsewhere also and other family members cannot hear it, then maybe you have tinninitus or are hearing your own high blood pressure blood flow (seriously). This commonly gets more acute at night when it is quiet, so all you are hearing is your internal ear sounds. I had this happen once because of a middle ear blockage - drove me crazy, getting up in the middle of the night because I thought I heard a water leak through the walls. Try putting on a pair of earmuffs or hearing protectors - if you still hear it or hear it louder, this is probably the case.

One method if hum is on the clearly audible side is make a 2 foot long cone out of paper to hold against your ear - like an antique hearing horn - then in each room face each of 4 directions while listening for where sound is the loudest, and turn your head to pinpoint the exact direction - I would spend 10 minutes doing this before getting into detailed stethoscope listening.

Otherwise, sounds like time for the old stethoscope (about $12 at a drug store - get a metal soundhead one, not cheap plastic, which does not pick up vibration as well). Also, if you are older (say over 35 or so) your hearing might have started to deteriorated with age, so if you have children or grandchildren with sharp hearing, they might be able to help track it down. I am sure a young child or grandchild, if you have one, would love this sort of treasure hunt (with appropriate "treasure" for a reward for tracking it down). 

Being careful not to come in contact with electricity with the stethoscope, check all the likely sources listed below. Start by placing it against pipes and walls and floor in each room of the house - water sourced noise goes a long ways, and tends to reverberate in the walls, so if that is the source likely to hear pretty easy. Hold stethoscope against bare pipes, both hot and cold, and heating system radiators or hot air vents.

If listening to water and hot water heating pipes indicates it is not water sourced, then you could turn off the master (outside) breaker or all the inside breakers and see if it goes away. I would only do this during above-freezing weather and early on a weekday, just in case a breaker fails to turn back on correctly when you switch it. Older master breakers particularly, which typically have never been used, sometimes break or fail to reclose properly after being shut off, so then have to be replaced. You want to be doing this at a time of day when, if necessary, you could get an electrician in the same day to replace it without paying weekend or nighttime emergency call rates.

If turning off the master breaker (or all other breakers) eliminates the hum, then turn them on one at a time until you find the one that turns the hum back on, then track where that circuit likely feeds (hopefully it is labelled) and check every switch, outlet, and light fixture.

Humming sources include (not in any particular order, a + in front means likely or common source of humming, - means rare or not likely):

1) + toilet fill valve - slightly leaking toilet inlet valve (listen where water tubing comes into toilet tank, and look inside tank to see if there is any water flow into or ripppling of the water in the tank or the bowl, or from the bowl filling tube (usually a small black plastic flexible tube which comes out of the fill valve (usually far left side of tank) and is clipped onto and discharges down into a hollow vertical brass or plastic tube or pipe in the toilet tank, which refills the toilet bowl after you flush)

2) + leaking faucet - kitchen, tub, shower, sink, utility tub, etc - it is amazing how just the smallest valve leak can make a hum or hiss that you can hear through the walls (especially at night), but only drips every few seconds.

3) - electric service meter dial motor

4) - electric breaker panel - rarely, a loose main power feed to a panel (especially with aluminum main service wire) will get loose enough that it vibrates back and forth and hums in its connector. A loose bus or snap-in breaker slot cover plate in the panel can also do this rarely

5) - gas meter or overpressure vent (unlikely, as you have had it replaced)

6) + boiling in the bottom of hot water heater or boiler because of buildup of lime, but would usually be intermittent - only when unit is heating

7) + furnace fan or electrostatic filter (forced air heat), or circulating pump (hot water baseboard heating), or steam condensate pump or overpressure venting (steam system).

8) - gas control valve or electric control box on a gas furnace, or its transformer (most have a 120V to 24, 16 or 12V transformer inside the front of the furnace

9) + air filter or electrostatic filter alarm on forced air furnace - some have a passive "whistle" opening that sounds softly when the filter is getting blocked, and if blocked with dust could make a hum rather than a whistle.

10) + Some water softener systems also have an "alarm" device to tell you it is time to service the unit, so check that if you have such a unit.

11) - a slightly leaking overpressure/overtemp valve on hot water heater or furnace (would be dripping)

12) - air venting from the air vents on hot water heating system. These will commonly make a hum or wheeze sound, for only for a few seconds at a time - not continuous unless leaking water

13) - city water system booster pump sound through the water column (if there is one near your home) - listen at the incoming water pipe - if much louder there than at other pipes within the house, that could be a house, though unlikely. If you think this could be it, find your water shutoff valve (typically 10' into your lawn from the street) and listen there. Would also be audible at neighbor's service pipe if that is the source.

14) - gas system compressor sound coming through gas pipe - listen to gas pipe outside the house and inside the house near furnace - if louder outside,, this could be a possible source, but the compressor or pressure reducer would have to be near your house. Would also be audible at neighbor's service pipe if that is the source.

15) + auxiliary booster circulating pump in your hot water or steam heating system (there may be one separate from the furnace, likely in the basement or a utility closet - most commonly found on  multi-unit apartment building with central heating and in 3 story or higher buildings, but you never know)

16) + a water leak, either inside or a leaking hose bib or pipe, or in your service pipe coming to the house

17) - electric on-demand water heater or electric-powered water filtration unit under the kitchen sink or inthe basement

18) + refrigerator compressor or fan hum

19) + doorbell transformer (front or back door - transformer is usually NOT at the doorbell, it is usually mounted in an open space like nailed to a basement joist, in an entry closet, or in the cubby space under the stairs - always physically near to the door, but NOT always on the same floor)

20) - any instant-on device like a TV

21) + any audio device (stereo, iPod, music player dock, computer, etc) that may have been left on at very low volume. Also, VERY rarely, if stereo or external speaker wires are run close to and parallel with an electric wire in the wall, they will acquire an  inductive voltage and hum.

22) + anything with a transformer, including stereo, add-on computer or iPod speakers, battery charger (rechargeable batteries or spare car battery or rider mower or boat battery charger), any portable electriconic device. Also portable device chargers (computer, iPod, cell phone, etc) - even if the device is not plugged into the transformer, as long as the transformer (charger) if plugged into an outlet, it is transforming high to low voltage, and transformers commonly hum

23) - electric typewriter left running

24) - electric ultrasonic cleaner or denture cleaner or electric toothbrush left on 

25) - home hair drying hood left on

26) - a lint buildup-jammed bathroom, kitchen, or attic fan. Many of these have, for safety, so called "self limiting" motors that if they jam just sit there and hum, but do not burn out.

27) - an attic cooling fan whose thermostat has failed, so is on all the time

28) - electronic furnace thermostat

29) + air conditioning unit, or aquxiliary air conditioner evaporator

30) + humidifier / dehumidifier - either permanently installed or portable

31) + portable heater / fan / air purifier

32) - automatic animal feeder waterer - either water supply or electric, as applicable

33) - dishwasher motor runningcontinuously - not shutting down after end of cycle

34) - convective or direct-vent oven or cooktop exhaust fan not shutting off

35) + flourescent (tube or CFL) or sodium or halogen light bulb / ballast hum (either inside, outside front door fixtures, or public street lights). These can hum quite pesistently when the starter circuit sticks on, or the bulb is dying and will not start (light completely), so the started circuit tries continually to start the lamp - can make a hum audible up to a block away on street lights.

36) - a dying electronic photocell designed to turn on your outside lights

37) - home security system, especially its alarm or horn. If the alarm is sounding but for some reason the main power is not getting to it, then as the battery goes dead (or if full voltage is not getting to it) is can give off a squeek, hum, or rasping sound - ditto if insects like wasps or hornets build a nest in it, so it cannot sound correctly.

38) + well pump, pressure tank, or filtration system, if you are on a well

39) + insect or bat nest in the attic or walls or in outside bins or cupboards, electric panel/meter, or outside telephone connection box (bees /wasps / hornets most likely) - though this usually varies by time of day, although it would "pulse" at the time of day when they are waking up or going to sleep.

40) + carpenter ants or termites - their continuous chewing of the wood can sound like a hum till you get right up against the colony, then you can actually hear the chewing

41) - a regional hum, as has been occurring at times in Ohio, Wisconsin, and Arkansas - where micro-seismic activity causes a hum or booming sound. Google or call your local paper and see if anyone has been reporting this in your area.

42) + outdoor power service transformer - either a metal (typically army green or gray) about 1 foot diameter "can" mounted on a power pole if you have overhead service, or a 2-3 foot cubic metal box on the ground or in a manhole pit near the street if you have underground service, which usually serves 4-6 houses (so may be in a neighbor's yard) and will have a voltage rating marked on it, usually in yellow stick-on lettering - like 4160V - 220V. Usually has high voltage - keep away safety markings on it.

43) - you have found where the Caddyshack gopher (who hummed to himself) moved to after Bill Murray blew up his happy home at the golf course.

Hope this list helps you (and future users with the same question).

Unless you feel uncomfortable doing minor repairs or don't understand that you should turn the electicity OFF before doing such installations...you can do the job yourself with a screwdriver and needle nose pliars...within 15 minutes. 5-10 minutes if you've done it before.

The amperage is the rated power it can handle. Modern houses are generally built with 200 amp panels, and a lot of the newer ones are going 300-350 amps as more and more electronic devices and fancy and high-demand kitchen devices and increased lighting are used in homes.

Both are just as safe - the 200 amp one will just have many more breaker slots, allowing way more circuits, and providing more room for expansion in the future, especially for power-hungry things like shop tools. Each uses only as much electricity as is used in the circuits - the panel itself does not consume any electricity, so no long-term impact there. It is just a circuit connection box where the individual circuits are connected, with circuit protectors (breakers) in line before it connects to the main line to your electric usage meter.

Unless you are real tight on money on this job, I would upgrade to 200 amps capacity - the incremental cost is about $100-200 or so over the 100 amp panel. If your incoming power line cannot handle 200 amps, you could install a 100 amp main breaker to keep the power company happy but put in the 200 amp breaker panel, so in the future a main line upgrade could be done with only a main disconnect breaker upgrade of $100 or so, without having to change anything inside the house.

Having the larger panel, especially if 200 amp capacity all the way from the meter, can be a selling point (or rather, lack of a negative point) to a potential buyer with lots of electronics or who is into shop power tools. It would also facilitate conversion to electric heat / water heating if someone wanted to do that.


As I understand it, you are looking at putting in a fan where there is no ceiling electric outlet. Since I am not sure, will try to break out piece by piece, undersanding these wouyld all be lumped into one job (possibly excluding wiring new outlet and switch). I hate to be so general, but access is the key here - if access is easy and there is a suitable light switch in the same room, cost can be at the low end of this range. If assess is poor and you don't want holes knocked in your drywall, then get more expensive real fast.

1) cost of fan typically $125-250 unless high end model

2) remove existing regular 4" box, install supports to joists and new box (ceiling fans need specially supported boxes due to the extra weight and swaying motion of the fans) $50-75

3) tap electric from existing circuit at existing box, upgrade existing light switch box to add one or two more switches (Adjustable for fan speed, 2nd for light, if so equipped), run wiring to ceiling fixture $125-250

4) put up fan, connect, test $75-100

So - total About $250-425 with no box there now, plus cost of fixture. A simple install to replace an existing fan, or install where the ceiling box was wired for a fan, would be only about $75-100.

This all assumes the existing nearby electric circuit can handle the addition of the fan - if not, then wiring cost will go up. It also assumes there is access via open attic or joists to install the wiring. Otherwise, installation cost OK but does NOT include repair to holes in drywall or ceiling to pull wiring.

Note also that an existing ceiling light box would probably NOT fill the bill - code in almost all jurisdictions requires 12 ga wire for fan motors, most household circuits are 14 or 16 gauge, so would need new wire pulled from a circuit with adequate capacity.

Get bids ! I worked on one job where the owner in a high-end house decided to put in fans with fancy candeliers underneath after construction was done - cost almost $3000 to do installation because all the wall and ceilings were finished in a high-end finish, so all wire pulling had to be done remotely - including removing siding to put in pull boxes at changes of direction and fasten conduit to studs. PLAN AHEAD !