Unit 7 Electrical Systems

Many jurisdictions require the service entrance wires to extend at least __________ inches out of the service cap at the top of the conduit or masthead. This gives the utility enough room to make the connections and leave a drip loop.

30 inches

Some large homes, farms, and many commercial buildings have four wires coming from the utility. This is called a three-phase system and is beyond the scope of this book. Three-wire service drops are called single phase. T or F

True

What wire in the electrical system is the grounding electrode conductor?

the bare wire that connects the service box to the grounding rods or water pipes or sometimes called the earth ground. 6awg

What wires in the electrical system are called equipment grounding conductors?

the bare wires that are in each branch circuit. or simply called ground wires

The size of the electrical service is a function of both the _______ and ______________. For 999 out of 1,000 houses, the voltage is 240 volts; 120-volt service is becoming very rare.

voltage amperage

Where Does the Grounding System End? The goal is to get the electricity to flow to ground. There are several ways to do this, including

-through metal water supply pipes; -through metal rods driven into the ground; -through wires (often ½-inch reinforcing bar) buried in -the footings of buildings (UFER ground); -buried grounding plates or rings; -the frames of metal buildings (more common in ---commercial than residential construction); and -the metal casings of private water supply wells.

The wires need only be ______ feet above a walking surface, ______ feet above a driveway, and ________ feet above a roadway. Wires near swimming pools must be 22½ feet away in any direction from the water.

10 12 18 22 1/2

Modern electrical codes require that wires be ________ feet away from the sides or bottoms of windows, doors, or fire escapes. This is true in some jurisdictions whether the windows open or not, because fixed windows may be replaced with operable windows in the future.

3 feet

wires can be run over house roofs if they are at least 8 feet above the roof or 10 feet above a walk-out deck. Wires over a roof with a slope of more than _______in __________ only have to be 3 feet above the roof. If the wires only project 4 feet onto the roof, they only have to be ________ inches above the roof.

4 in 12 18 inches

CUAL

A designation for aluminum-compatible equipment.

overfused

A fuse or circuit breaker that is oversized for the capacity of the circuit conductors.

fused neutral

A common problem in old panels. The neutral (white) wire in the service box should not run through a fuse. The black wire should have a fuse, and the red wire should have a fuse, but the neutral wire should not

open splices

A connection between two or more electrical wires is called a splice and should connected inside electrical boxes. When the connections are not contained inside a box, it is called an open splice.

tie bar

A mechanical tie bar is used to join two breaker handles

ampacity

Ampicity is the maximum amount of electric current a conductor or device is meant to carry.

conductors

Any material used to conduct electricity; a current carrying wire.

bonding

Bonding is simply the act of joining two electrical conductors together. They may be two wires, a wire and a pipe, or they may be two tin cans. Bonding ensures that these two things will be at the same electrical potential. That means you won't get electricity building up in one and not in the other.

CO/ALR

CO/ALR stands for 'Copper Aluminum Revised'. Devices marked with CO/ALR mean that either copper or aluminum wire installation is appropriate

What If Wire Size Doesn't Match Fuse Size?

Determining the size of the breakers or fuses is not as reliable as sizing the service entrance conductors. The fuses or breakers and service entrance conductors should be a match in terms of their current rating, but they aren't always. Undersized fuses will cause you to report the service as smaller than it actually is, if you rely solely on the fuse size. This is not a safety concern because the fuses will cut off the electricity long before the wire overheats.

The service drop terminates at the ______________.

Drip loop

A home with 60 amp electrical service with a huge demand for power is a safety hazard when that demand reaches more than 60 amps. True or False

False If you use enough appliances at the same time, the total current draw through the red and/or black wires will exceed 60 amps and the main fuses or breakers will shut off the power. This is an inconvenience, but it isn't a safety hazard.

The white neutral wire is the ______________wire

Grounded

grounding

Grounding is the act of connecting something to the ground (earth), so it has zero electrical potential. Everything that is grounded is connected to ground and can have no electrical energy stored in it.

125- and 150-amp services are common in some areas on small houses with electric heat or larger houses without electric heat. They are also found on average-sized houses with more than a typical number of appliances. A 200-amp service would be found on an electrically heated home or a large house.

In rare cases, you may find a 400-amp electrical service. This is the largest single-phase service available. It's the largest service most utilities will put into a residence. The residence is probably more than 6,000 square feet, or quite large and electrically heated.

We are not allowed to use the gas piping to ground an electrical system. However, gas piping must be bonded to the electrical grounding systems in most jurisdictions. Bonding the gas piping is often accomplished with a wire attached to the cold (and sometimes hot) water supply pipe, near the water heater

Incidentally, bonding the gas piping usually bonds the furnace and ductwork too, because the piping touches the furnace. Bonding the gas piping is often accomplished with a wire attached to the cold (and sometimes hot) water supply pipe, near the water heater.

voltage drop

Loose connections also lead to excessive voltage drop. It's natural to have some loss, or drop, of voltage by the time you get to the end of a long circuit. Most codes allow this to be as much as 3% through a feeder or branch circuit, or 5% total through both. Loose connections lead to too much voltage drop, which might be noticed by dim lights, slow motors, et cetera.

insulators

Oppose electrical current and provide protection from electrical current.

resistance

Opposition to the flow of current in an electrical circuit; resistance is measured in ohms.

Let's look at some of the service drop problems you'll find: 9 things

Overhead wires too low Overhead wires too high Damaged or frayed wires Trees or vines interfering with wires Wires too close to doors or windows Wires not well secured to the house Poor connection between the service drop and service entrance Inadequate clearance from roofs Service lateral problems

Where the service is coming to the house from underground it is called what?

Service lateral

3 wires coming into a home from the service drop is __________phase.

Single phase

But it's more confusing than that. They don't use every number. For example, they only use 14, 12, 10, 8, 6, 4, 3, 2, 1, and 0. ( A good way to remember is to count by 2 backward from 14 to the magic number and than 3, 2, 1, 0.)

So, there is a wire size called 0 and the next bigger wire size is 00, sometimes shown as 2/0. The next size after that is 3/0 or 000. The largest size you'll see in most houses is 4/0 (used in some areas for 200-amp services where the service entrance conductors are aluminum)

Overfusing Unsafe

The fuses may be too large for the service entrance conductors. This would lead you to describe the service size as larger than it actually is, if you just read the fuses. This may be an unsafe situation because the fuses may not shut off the electricity quickly enough to keep the service entrance conductors from overheating.

Ground wires should not be spliced because every splice is a potential poor connection.

The ground wire is typically connected to the service box at one end and to a pipe and/or ground rods at the other. Make sure the wire is securely fastened at both ends. Where ground wires are attached to pipes, it's not adequate to just wrap the wire around the pipe. The wire must be secured with a clamp approved for that purpose.

Implications of no grounding system

The implications are as follows: No grounding Ground wire attached to plastic pipe Ground wire after (downstream of) meters and valves, with no jumper Spliced ground wire Ground wire attached to abandoned pipe Poor connections Ground connections not accessible Ground rod cut off Corroded ground wire Undersized ground wire Neutral bonded to ground wire after (downstream of) service box (sub panels should not be bonded) Neutral wires not bonded to ground wire at service box Service box not bonded to ground wire No ground in subpanel feeder wires

Fused Neutral

The neutral (white) wire in the service box should not run through a fuse. The black wire should have a fuse, and the red wire should have a fuse, but the neutral wire should not.

The only place that the neutral wire and the ground wire should be bonded together is at the service box. (newer construction it's going to be a combination panel) (breaker box) This will be discovered most often at auxiliary panels. (sub panels) Check that the neutral and ground wires are separated.

The neutral wire carries electricity every day. The equipment ground wires should not. If the neutral and ground are bonded together out in the house distribution system (for example, at an auxiliary panel), the equipment ground wires may carry some everyday electricity. This is not safe.

voltage

The pressure from an electrical circuit's power source that pushes current through a conducting loop.

Service Box and Distribution Panel Ratings

The service box and distribution panel have to be big enough to accommodate the service size. The box and panel can be rated for the same or more amps, but not less than the service size. (so my question would be, if the main breaker can undersized with no danger, why can't the distribution panel be undersized?)

line

The side of the device where the wires from the panel are connected.

There are two types of grounding in homes, with different functions. The equipment grounding system is the network of bare wires that runs through the home as part of the branch-circuit wiring

This grounding system is connected to the white or neutral service wire coming in from the street. This equipment grounding system protects people from electric shock when electricity gets somewhere it shouldn't and allows fuses to blow and breakers to trip. Think of this as an emergency path for electricity.

although wire is a single conductor and cable is a group of conductors

True

Most 240-volt circuits have a red wire, black wire, and white wire. However, some have only a red wire and a black wire. How can a circuit work with no white wire?

We talked about 240-volt circuits much earlier and said that when the red wire pulsed, the black wire was at rest, and vice versa. The red and black wires can act as white wires, but only if the load is exactly the same on the red and black wires, as for a baseboard heater or water heater. Any appliance that has a 120-volt component will need a white wire to carry the unbalanced part of the load. Stoves have 120-volt lights, clocks, and timers. Clothes dryers have 120-volt lights, timer, and motors. Air conditioners may have 120-volt motors and crank case heaters. All appliances with both 240-volt and 120-volt components need a black, red, and white wire.

What If the Fuse Is Too Small? If the fuse or breaker is too small, it will shut down the electrical system before it has to. A fuse that is too small will be a nuisance because it's likely to blow frequently, but it isn't a safety hazard.

What If the Fuse Is Too Big? If the fuse or the breaker is too big, it won't shut off the electricity soon enough. This may allow the wire to overheat and create a dangerous situation. Finding too large a fuse or breaker (often called overfusing) is probably the most common electrical problem you will come across. Even when breakers are being used instead of fuses, people still call it overfusing. You'll be better off referring to the issue as oversized fuses or breakers.

downstream

When a switch is located after the fuses, it is considered downstream.

load

Where the device that is to be protected by the GFCI device is connected.

From Service Drop to Service Equipment Service wires pick up where the service drop wires end. They extend down to the service equipment (main disconnect, service panel, service box). The correct name for these wires is ________________________.

service conductors

There will usually be ________ wires coming in through the service drop: two hot wires (typically black) and a neutral (white). Sometimes all three wires are black. The neutral occasionally also acts as the support cable for the hot wires. Sometimes there is a separate cable supporting the three conductors. The neutral wire may be bare (no insulation) and, in some cases, is smaller than the hot wires.

three

4 wires coming into a building is _________phase service.

three phase

If the main disconnect is fused, there will be two fuses in the service box. One fuse is for the red service entrance conductor and the other is for the black. If each of these fuses is rated at 100 amps, you have a 100-amp service. Be careful: you cannot add the two fuses together. A 200-amp service would have two fuses, each sized at 200 amps

true

Wires running over a flat roof that is used as a walking surface should be 10 feet above the roof. Otherwise, wires should be 8 feet above the roof. If the roof has a slope greater than 4 in 12, the wires have to be only 3 feet above the roof.

true

You may also be able to tell whether the wire is copper or aluminum. Aluminum wire always has the word ALUMINUM, the letters ALUM, or the letters AL written on the sheathing.

true