John Knouse's Electrical Tips
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This page was last revised on July 12, 2011
- Household current is a nominal 120 volts. This is the same as 115 volts or 110 volts. The
reason for this is that standards were originally set at 120 volts, but it was found that voltage drop
in transmission could cause a reduction in voltage, so appliances were made to be able to handle a
range of voltage from 110 to 120 volts. Any single circuit in a normal household has one live wire
and so is 120 volts nominal, while a circuit which is rated as 240 volts (or 230 or 220) has two live
wires, each with 120 volts nominal. You may see outlets or other parts rated at 125 or 130 volts
or at 250 volts. This just refers to engineering tolerances, and should be reassuring!
- Most houses with modern electrical service have three conductors coming into the house, and
they're twisted around each other. If you look, you'll see two black (insulated) wires and a bare
silver-colored cable. The two blacks are the hot, or live, wires, while the bare cable is the neutral,
or return wire. Each black wire is connected to a separate connector in your circuit breaker (or
fuse) box, resulting in two separate hot circuits that supply electricity to your circuit breakers.
Household electricity (in most cases in the US) is AC, or alternating current, and a graph of the
current shows a sine curve, or a wavy line. Each of the two circuits is 180 degrees out of phase
with each other, meaning that when one current peaks, the other is in a valley, and vice versa. A
220 circuit breaker automatically attaches to both of these circuits. A 220 circuit will not work
- Circuit breakers, on the other hand, are rated in amperage, or amps. Amps (amperes) are the
measure of current flow, while voltage is the measure of current push. Your meter, on the other
hand, measures kilowatt-hours, which is total usage. Think of it this way: If you have a water
pipe, the voltage is like the water pressure in the pipe, but the amperage is the size of the pipe.
How much water comes through the pipe is measured by watts, but is determined by both the
water pressure and the pipe size. With electricity, volts times amps equals watts. Watts measure
power. A kilowatt is just a unit of one thousand watts. And a kilowatt-hour is one kilowatt used
per hour. So if you use 48 kilowatt-hours in a day, that means that you're using 2 kilowatts per
- There are very standard color codes for household wiring. Black or red wires are ALWAYS
live or hot wires. White wires are almost always neutral wires--that is, their purpose is to provide a
"return" route for "spent" current coming from the hot wires. The one exception to white
wires being for neutral circuits is when they're used for switch legs. Green wires are ALWAYS
ground wires, and bare wires always should be ground wires, too. Sometimes you may see blue
wires, which color is sometimes used for additional hot circuits.
- In outlets or household appliances, there are usually two colors of screws. Silver-colored
screws are neutral screws, and brass-colored screws are hot screws. The white wire should always
be attached to the silver-colored screw, and the red or black wire should always be connected to
the brass-colored screw.
- Most modern plugs are polarized plugs. That is, one blade of the plug is specifically for the
hot contact and the other is for the neutral. The narrower blade is the hot and the wider blade is
the neutral. If it's a grounded plug with three prongs, the rounded one is the ground, and if you
look at the end of the plug with the grounded prong on the bottom, the neutral blade is on the right
and the hot is on the left. If you look at the outlet, the round hole is for the grounded prong, the
short slot is for the hot, and the wide slot is for the neutral.
- In lamps, which wire is hot and which is neutral is important for safety reasons. If you look in
a lamp sockets, you'll see that the metal shell, into which is formed the screw threads, is one
electrical contact, which is the neutral part, and that the other electrical contact is a little button in
the bottom which is the hot contact. In three-way lamps, there will be two buttons or metal pieces
in the bottom, and these are both hot. It's done this way so that you cannot shock nor electrocute
yourself while changing a light bulb. When replacing a lamp cord, be sure to use a cord with a
polarized plug. Some polarized cords have a white stripe on the neutral side. If a cord doesn't,
you can usually see impressed printing on the hot side. This makes it easy to tell at the lamp end
which wire is which.
- When considering 120 volt circuits, normal household wiring should always be at least 12
gauge. 14 gauge is allowed by law in many areas, but is often also the cause of electrical overload
fires. By the National Electrical Code, 14 gauge wire can be used for a 15 amp circuit, and 12
gauge wire can be used for a 20 amp circuit. Again, it is recommended that you use 12 gauge
wire for ALL 15 and 20 amp circuits. The ONLY place you should use 14 gauge wire, if at all,
is for switch legs, where the wire is supplying electricity to the light only.
- When considering 120 volt circuits, most household circuits should be on 15 amp fuses or
circuit breakers. Only kitchen circuits or special circuits for equipment should be on 20 amp
- GFCI means ground-fault circuit interruptor. It's also called just GFI. ALL basement circuits
should be on GFCI circuits, ALL bathroom circuits should be on GFCI circuits, outdoor circuits
should be on GFCI circuits if within six feet of the ground, and ALL kitchen circuits should be on
GFCI circuits, except for dedicated appliance circuits that are at least eight feet away from the
sink. There are two ways to provide a GFCI circuit: 1) Install a GFCI outlet as the first outlet in
the circuit (closest to the circuit breaker or the fuse), and make sure that all other outlets in the
circuit are downstream from this (and the way to test this is, when you've installed it, with the
circuit breaker on, press the "test" button on the GFCI outlet, and all the other outlets should then
go dead); or 2) Install a GFCI breaker for the whole circuit (and it will have a wire coming out of
it, unlike other circuit breakers; this wire should go to the neutral bar in the circuit breaker box).
- Three-wire circuits, using a white, a red, and a black wire, can be used to supply electricity
from two circuit breakers--but ONLY when the circuit breakers are "stacked" in the
breaker box--that is, one is right below the other. This ensures that each circuit is out of phase
with each other, which is the only safe way to use a common neutral wire.
- When installing a new cord to a 220/240-volt appliance, there's usually a flat cord with three
conductors. The middle conductor is the neutral, and gets attached to the silver-colored screw
(usually the one in the middle). The two side conductors are the hot ones, and get attached to the
brass-colored screws. It doesn't matter which hot conductor gets attached to which side, as long
as the neutral is properly on the neutral. Of course, the cord may have white, black and red wires
in it; in this case, again, the white is the neutral, and it doesn't matter which screw the black and
the red are on as long as the white is on the correct screw.
- Computer equipment should NEVER be on the same circuit as heaters, air conditioners, any kitchen appliance, or
any major appliance. The power fluctuations induced by these devices are really, really bad for your computer
equipment which is, after all, a MAJOR investment. Ideally, computers should be on their own circuit. Use a good-
quality surge-suppressor power strip to plug everything into. This is good, cheap insurance for protecting your computer.
A computer power supply is usually rated at around 5 amps, and monitors are rated from 1.5 amps on up. Add in a
printer, a speaker set, maybe a workstation lamp and whatever, and pretty soon you're loading down a whole circuit
pretty thoroughly. If on a shared circuit, though, it's generally pretty safe to use a circuit that also serves just lights,
clocks, and radios, such as in a bedroom. Just make sure that the total load isn't too much for a circuit.
- It's also a good idea to have dedicated individual circuits for your refrigerator and for air conditioners, so that these
aren't inadvertently switched off if something else on the circuit causes an overload. In the case of air conditioners, it's
best to have a 220V circuit, and to use a 220V air conditioner. They work better, last longer, and cost less to operate.
- When running circuits on the outside of a building, be sure to use exterior-rated connectors and devices. It's a
common mistake to use interior-type components for exterior use. Exterior EMT connectors have plastic seals in them,
and elbows have weather-resistant gaskets, as do electrical boxes and covers. Use teflon tape when threading together
components. Carefully and thoroughly paint any bare EMT or plastic conduit immediately after installing it. Try to use
bends in EMT rather than elbows to preserve a good weathertight seal. Make sure that the placement of all lines and
boxes is is in as sheltered a spot as possible. For instance, rather than running conduit along the side wall of a house,
run it as far up under the eaves as possible, where it's really sheltered. Make sure that electrical boxes, such as for
outlets, are not where rainwater will drip on them or the wind will blow rain onto them. This is especially important for
light sockets. Light bulbs and photoelectric or motion-sensitive switching devices will fail very quickly if they're situated
where water gets into them easily. And, of course, any exterior outlets should be GFCI-protected.
- When running electrical wires to a spot away from the house, such as to a detached garage or shop building, the best
practice is to use plastic conduit that's rated for underground use, and bury it at least eighteen inches deep. Conduit is
better than plastic pipe, especially since the bends have large radiuses and so make it easy to pull additional wires
through them. Make sure that you use the proper type of primer and glue on the plastic conduit, and
that it's securely glued. Make sure that the conduit has a slope that allows the entire run to drain to a common drain
point; this can be into your basement, for instance, near a floor drain. If you're running wiring to a detached garage or
shop building, it's a good idea to run heavier wire and then to install a secondary circuit breaker box in the garage or
shop building. 10/3 wiring will allow you to install four 15-amp breakers or two 20-amp breakers, running from a 30-amp,
double-pole breaker in the main box. 8/3 wiring will allow four 20-amp breakers or six 15-amp breakers, running from a
40-amp, double-pole breaker in the main box. 6/3 wiring can serve six 20-amp breakers or eight 15-amp breakers,
running from a 60-amp, double-pole breaker in the main box.. Be sure that you understand that this configuration is
based on the secondary circuit breaker box having two hot circuits, each separately supplied by a hot wire, with a
common neutral, and with the circuit breakers being EVENLY divided between these circuits. It's also
recommended that you have a separate ground running from the secondary box. It's also a good idea to use GFCI
breakers in such a situation.
- Appliances made for foreign markets mostly won't work properly in the US and may even cause a fire hazard. For
instance, much of Europe and a number of other countries use 50-Hertz power supplies, whereas we use 60-Hertz.
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