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bryan1282 09-29-2009 12:13 PM

BX Wire Problems
i wanted to move some switches, the house is bx cable or armored cable whatever you prefer. it was built in the 60's and the wires are white/black, or for the 3-ways, white/black/red. it has the aluminum strip that wraps around the metal sheathing that serves as the "ground". the breaker box is grounded to the water pipe in the basement. i havent had a ton of experience with a/c cable mostly just romex. My question is how to extend the wire? can i use romex or mc cable with the green ground wire? metal or plastic boxes? through books online and other diy help, i have heard use the mc cable and metal boxes, connect black to black white to white and the green ground wire to the metal box with a screw? thanks for your help and input!!
p.s. or should i try to find the ac cable with the bonding wire? seems hard to come by.

kok328 09-29-2009 03:33 PM

As long as the BX cable is copper wire and not aluminum, you can use NM or MC cable with ground wire in a plastic or metal box.
black to black, white to white and green to green (if using MC) or bare to bare if using NM.
if using a metal box, ground to box and bare NM (or green if MC).
all splices must be enclosed in a jbox (plastic or metal).

Nestor_Kelebay 09-29-2009 04:38 PM


You sound like you could use a basic understanding of electrical wiring.

Before you start doing any switches or recepticles, take a read through the following two posts I wrote for people on other forums:

Welcome to 220 volts, class 101:

The wires that run overhead to your house carry 220 volt power. That 220 volt power is delivered via two power lines and a neutral wire. The two power lines each carry 110 volts AC, but they are "out of phase" by 180 degrees. That is, when one power line is at +110 volts with respect to the white neutral wire, the other power line will be at -110 volts with respect to the white neutral wire, and vice versa. So the voltage you would measure between the two power supply lines would be 220 volts AC. On appliance wiring diagrams, the two power lines will typically be called "L1" and "L2" for "Line 1" and "Line 2". In practice, Line 1 and Line 2 will ALWAYS be the red and black wires (meaning the insulation on them will be red or black in color), and the neutral wire is ALWAYS white. Grounding wires will be green or bare (with no insulation).

The standard 110 volt circuits for the ceiling lights or electric outlets in your house are made by connecting those circuits between the white neutral wire and EITHER the main red wire OR the main black wire coming into your house. All of those connections are made in your electrical panel and a fuse or circuit breaker is provided for each such circuit in your house. So, some of the 110 volt circuits in your house that go to lights or electric outlets are powered by the red wire, and some are powered by the black wire. As long as the circuit is between the red wire and the white wire, or between the black wire and the white wire, you have a 110 volt AC circuit. If you put a 15 amp fuse or breaker on that 110 volt circuit in the panel, then you have a 110 volt 15 amp circuit, and normally the circuits going to the lights, ceiling fans and electrical outlets in your house will be 110 volt 15 amp circuits.

220 volt circuits for the house's electric stove and electric clothes dryer are made by connecting the circuit between the main black and red wires at the electrical panel. Both the red and black wires carry 110 volts AC with respect the the white neutral wire, but because they're 180 degrees out of phase, there's 220 volts AC between the red and black wires. So, if you connect a circuit between the main black and main red wire going into the house, then you have a 220 volt circuit. If you're wiring a range, you normally need a 50 amp circuit, which requires a 50 amp breaker on BOTH the red and black wires going to the range. If you're wiring an electric dryer, you need a 30 amp circuit, so that means you must have 30 amp breakers on both the red and black wires going to the dryer. The fuses and breakers that control the current through every circuit are located inside your house's electrical panel.

When you open a typical electrical panel you'll notice that the fuses or circuit breakers are typically arranged in two vertical rows; one on each side of the panel. Do not assume that one side of the panel is for tapping off the red power line and the other is for tapping off the black power line. The buss bars inside the electrical panel determine what gets connected where, and often breaker positions above one another on the same side of the panel will be connected to opposite voltage sources. This is done so that the circuit breakers can be "ganged together" so that you can't flip the breaker off to one power line going to a stove or dryer without turning the power off to BOTH power lines. In Manitoba, where I live, the electrical code requires that circuit breakers for 220V appliances be "ganged" together in this way for safety reasons.

The technically incorrect but easiest way to think about this is that the power comes "in" on the red and black wires and goes out on the white wire. Obviously it doesn't, but that way of thinking about it will at least help you better understand house and appliance wiring and the reasons behind doing certain things certain ways. For example, there is a standard wiring convention when wiring 110 volt electrical outlets. You will notice that the screw connections on one side of the duplex receptacle will be chrome plated, whereas those on the other side will be bare brass. Always connect the light coloured wire (white) to the light coloured screw (chrome plated), and the dark coloured wire (red or black) to the dark coloured screw (bare brass). If homeowners, electricians and appliance manufacturers all follow this wiring convention, that will ensure that the on/off switch for 110 VAC appliances will always be on the power supply wire (that is, the red or black wire). And, this is important from a safety perspective because it ensures that the on/off switch will shut off power from coming into the appliance. Before both electrical plugs and receptacles were "polarized", both the prongs on a plug and the slots in a receptacle were the same size. So, you could plug a 110 VAC appliance into a receptacle with the plug either right side up or upside down. The appliance would work equally well either way. However, in one of these positions the on/off switch of the appliance would be on the power supply wire and would shut off the power going into the appliance. In the other position, the on/off switch would be on the white wire and would shut off the power coming out of the appliance. So, if there were a short circuit in the appliance, having the switch on the power supply wire would ensure that there would be no power in the appliance when the switch was in the off position. But, if the plug was upside down, and the on/off switch were on the white wire, then there would ALWAYS be power in the appliance as long as it was plugged in, and you could still get a shock from the appliance even if it was turned off. That's cuz the switch is now only preventing power from leaving the appliance via the white wire. The power can still come into the appliance via the black or red power supply wire and leave the appliance via some other route, like through YOUR BODY!!! Thus, if you happened to be turning a faucet off while you were handling a faulty toaster, you could end up getting 110 volts at 15 amps across your heart even if the toaster was off at the time. Thus, by sticking to this dark wire/dark screw wiring convention, we always end up with the switch on the power supply line, and that keeps things safe.

There is also a standard wiring convention used when wiring the plugs, receptacles and terminal blocks of 220 volt appliances, all of which will have provision for connecting THREE wires as well as a ground wire. Normally the ground wire terminal will be easy to identify because it will be grounded to the electrical box by an electrical conductor, and the remaining three connection points for the red, white and black wires will be arranged in a row. The wiring convention is that the white neutral wire is ALWAYS connected to the middle terminal in that row of three connection sites, and the red and black wires are connected on either side of it. It doesn't matter which side you connect the red or the black wires to, as long as the white is in the middle and the red and black are on the outside, you're good to go. If your stove or dryer doesn't come with a cord and you want to connect one to the terminal block of the appliance, the same rule applies, namely "white in the middle, black and red on the outside". If you're wanting to wire a receptacle for a stove or electric dryer, then again, the same rule applies. First identify the ground wire terminal, and the remaining three connection points will be for the red, white and black wires and they should be arranged in a recognizable "row". Always connect the white in the middle of those three sites and the red and black on either side of the white. This point has now been officially hammered into your head; white in the middle, black and red on either side.

Every dryer cord will have 4 prongs sticking out of it. The straight ones are for the red and black wires, the "L" shaped one is for the white wire and the round one is for the ground wire. Range cords also have 4 prongs, but they will use 3 straight prongs for the red, black and white wires and a round one for the ground wire. Configuring the plug and receptacle differently (with an "L" shaped prong instead of a straight one) is done so you can't stick a 30 amp dryer plug into a 50 amp range receptacle or vice versa.

Nestor_Kelebay 09-29-2009 04:39 PM

The heating elements in both electric dryers and stoves require 220 volt power, but you still need to run the white wire to the stove or dryer. The reason why is that there will be circuits within the stove or dryer that require only 110 volt power. For example, the electric motor that turns the dryer drum or the light bulb inside an oven will both require 110 volt AC power, not 220 volt power. So, in an electric stove the heating elements will be connected between the red and black wires because they need 220 volts, but the electrical outlets provided for convenience on the stove console will be connected between the white wire and either the red or black power wires, because the convenience outlet is intended to provide power to 110 volt appliances. And, this is also why you can have TWO convenience outlets on a stove instead of just one. One of those convenience outlets will be powered by the black wire, and the other one by the red wire. Since the main black and red wires going to a stove are fused at 50 amps each in the electrical panel, any circuit between the red and white OR black and white wires in the stove will give you a 110 volt 50 AMP CIRCUIT which probably won't stop pumping out the electricity if there's a short somewhere in that circuit, and 50 amps going through wiring rated at 15 amps is a great way to start a fire. That's why for the electric outlets provided for convenience on range cooktops, there will be a 15 amp fuse right in the range somewhere that fuses each convenience outlet down to 15 amps. If you have two cooktop plugs, one will be driven by the red wire and one by the black wire, and each will have a separate 15 amp fuse on it.

Also, if you stop to think about it, if the black supply wire is feeding a 110 AC voltage sine wave into the white "return" wire and the red "supply" wire is also feeding an equal but opposite voltage into that same white "return" wire, then theoretically, there should be no voltage in the white wire since the two sine waves would cancel out. Similarily, the resultant current sine waves from the red and black wires would cancel each other out when they both meet at the white "return" wire. If the world was perfect and all electrical loads were purely resistive, like light bulbs, toasters, electric ranges and coffee makers, then the voltage and current sine waves from the two power supply wires would indeed cancel each other out, and there would be theoretically be ZERO voltage and ZERO current in the white wire. However, the world isn't perfect, and professional wrestling isn't real and Lassie has started killing chickens. In the real world there are electric motors and television sets and computer monitors, all of which have some "impedance". In an electric motor, for example, the magnetic fields created by the electric motor windings impeded the flow of current through those same motor windings, so the motor windings themselves cause the current sine wave coming out of the motor to lag behind the applied voltage sine wave. Also, television sets and those old CRT style computer monitors have huge capacitors in them. In a capacitor, the current OUT of the capacity is highest when the CHANGE in voltage is highest, and that occurs when the voltage sine wave passes through the point of ZERO voltage. Thus, capacitors cause the current sine wave coming out of those computer monitors and TV sets to actually preceed the applied voltage sine wave. So, even though the red and black wires carry equal and opposite 110 AC voltage sine waves, the impedance of "reactive" loads like electric motors and TV sets causes timing differences in the resulting current sine waves coming out of those loads. So, the current and voltage sine waves generally DON'T cancel out in the white wire, and there can be significant voltages and currents in the white wire. So, to be safe, treat every wire as having dangerous voltage in it.

There is also a wiring convention when wiring 110 volt 15 amp electrical outlets. Since those outlets are always connected between either the red and white wire or between the black and white wire, the connection screws on the outlet will be "colour coded" to ensure you connect the right wire to the right screw. You'll notice that the connection screws on the two sides of electrical outlets will be bare brass on one side and chrome plated on the other side of the outlet. The convention is that you connect the dark wire to the dark screw and the light wire to the light screw. That is, the red or black wire gets connected to the brass screw and the white wire gets connected to the chrome plated screw.

The reason for having this convention becomes obvious when you consider the old two prong plugs and two prong receptacles that had both prongs on the plug and both slots in the receptacles the same width.

What would happen if you had a short circuit in an appliance like a hair dryer or kitchen mixer? If you plugged that appliance in with the plug one way (that we'll call "right side up") then the switch would be on the plug prong that connects to the black or red wire in the house wiring, and as long as the appliance was turned off it would pose no risk of shock because the switch would prevent power from getting into the appliance. However, if you were to unplug that faulty appliance and push the plug in "upside down", then the other prong of the plug would be connected to the black supply wire. If there were a short circuit in that appliance, then you could get a shock from touching that appliance even though it was turned off.

The whole idea behind "polarized" plugs and receptacles is to ensure that the black or red wire carrying power to a receptacle will always connect to the prong of the plug that the appliance's ON/OFF switch is on. That way, as long as the appliance was turned off, it posed no risk of shock.

This may seem like a trivial matter, but it isn't. If you have an electric shaver or curling iron you use in a bathroom, and it has a non-polarized plug, then if there's ever a short circuit in that appliance then it can be energized with 110 volt power even when it's turned off. So, you can get a shock just by touching it and a plumbing fixture at the same time.

So, the wiring convention of connecting the dark wire to the dark screw and the light wire to the light screw on an electrical outlet ensures that the red or black power line always goes to the narrower slot on the electrical outlet. And, as long as appliance manufactures follow the same convention and put their ON/OFF switches on the wire going to the narrow prong on the appliance's plug, then you can always turn off the power to an appliance by shutting it off at the ON/OFF switch.

dodge2000 09-30-2009 08:58 AM

Boy the others, sure gave you a lot of information, bryan1882

First are there any local or state electrical codes the would prohibit the
use of NM-B/romex cable for use in this wiring project.

If the answer is no, then I would use romex cable for all runs that were
not exposed. It is so much easier to work, with.

You can use plastic or metal boxes with it. Metal boxes requires grounding.
Plastic no require any grounding. But then you must ground to you switch/

Nestor_Kelebay 09-30-2009 11:38 PM


PS: That 110 VAC wiring convention posted above also applies to other 110 VAC wiring, like plugs and cord ends. If you're replacing the plug on the end of an appliance's cord, or the female (or male) cord end on an extension cord, the same rule applies; darker black wire to the darker copper screw and white wire to the lighter chrome plated screw.

Just though I'd drive that point home cuz wiring your house receptacles correctly (or according to the convention) won't matter if the wiring in the plugs or extension cords you plug into those receptacles is done wrong (or not according to the convention).

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