Wire -- Selecting and Connecting


Wires are used as conductors. A conductor is any material that can carry the flow of electric current. The terms wire and conductor are used interchangeably in this book. Insulators are materials that don’t conduct electric current. Metal wire is enclosed in insulating material such as plastic to help protect against stray current. Electricity flows more easily in some materials than others. Copper wire is the best material for ordinary purposes. If iron wire were used, it would have to be about ten times as large in cross-sectional area as copper wire. Other conductors include cable and busbars. Humans and animals can accidentally become conductors resulting in electric shock, so always use caution when working with electricity.

All references in this guide are to copper wire, except in the discussion of aluminum wire later in this Section and in Section 19.


Copper wire sizes are indicated by number—the larger the number, the smaller the wire. See Fig. 4-1. The most common size for house wiring is 14 AWG, which is not quite as big as the lead in a pencil. Numbers 12, 10, and 8 AWG and so on are larger than 14 AWG; 16, 18, and 20 AWG and so on are progressively smaller. Number 14 AWG is the smallest size permitted for ordinary house wiring, and 1 AWG is generally the heaviest used in residential and farm wiring. Still heavier sizes are 1/0, 2/0, 3/0 and 4/0 AWG, the 4/0 being almost half an inch in diameter. Numbers 16 and 18 AWG conductors are used mostly in flexible cords and the still finer sizes are used mostly in the manufacture of electrical equipment such as motors. Number 18 AWG is also commonly used in wiring doorbells, chimes, thermostats and similar items operating at less than 30 volts. Wire of the correct size must be used for safety and efficiency as discussed below in terms of ampacity and voltage drop.

Fig. 4-1: Approximate diameters of different sizes of copper wire, without the insulation.

Ampacity: Ampacity is the safe carrying capacity of a wire as measured in amperes. When current flows through wire, it creates a certain amount of wasted heat. The greater the amperes flowing, the greater the heat. Doubling the amperes without changing the wire size increases the amount of heat four times. To avoid wasted power, a wire size that limits the waste to a reasonable figure should be used. Of even more concern, if the amperage is allowed to become too great, the wire may become hot enough to damage the insulation or even cause a fire. The National Electrical Code (NEC) is not concerned with wasted power, but it’s concerned with safety; therefore it sets the ampacity -- the maximum amperage that various sizes and types of wires are allowed to carry

Conservative ampacities for common wire sizes are shown in Table 4-1. For larger sizes, consult NEC Table 310.16. Insulation types are described under the “Wire Types” heading in this Section. Equipment and devices (circuit breakers, switches, panelboards, etc.) have been tested, unless otherwise marked, at the ampacities in Column A of Table 4-1 up to 100 amperes and in Column B over 100 amperes, so even though the NEC tables might indicate the conductor has a higher ampacity, the termination may limit the ampacity to those shown. Column C covers conductors with high-temperature insulation (90°C). Although these wires are very common today, the termination rules tend to limit the usable current in these wires to the amounts in Columns A and B as noted.

Conductors have different ampacities for each variation in ambient temperature, proximity to other conductors, type of insulation, depth of burial, etc. Variations in ambient temperature are covered in the NEC by the correction factors at the bottom of NEC Tables 310.16 through 310.19. Adjustments to ampacity due to numbers of conductors in the same raceway or cable are covered in NEC 310.15(b) (2). Ampacity calculations are some of the most complex in the Code; however, for simple home and light commercial work, the values in Table 4-1 should suffice.

Voltage drop : If forcing too many amperes through a wire only caused a certain amount of wasted power, we might consider it a mere nuisance and minor loss. However, it also causes voltage drop. Actual voltage is lost in the wire so that the voltage across two wires is lower at the end than at the starting point. For example, if you connect two voltmeters into a circuit, as in Fig. 4-2, one at the main switch and one across a 1-hp motor at a distance, you will find that the voltage at the motor is lower than at the main switch. The meter across the main switch may read 120 volts. If 14 AWG wire is used to the motor, the voltage across the motor terminals will be about 119 volts if the motor is 10 feet away, but only about 112 volts if it’s 100 feet away. The difference is lost in the wire and is known as voltage drop. Voltage drop is wasted power, but there is another important consideration:

appliances work very inefficiently on voltages lower than the voltage for which they were designed. At 90 percent of rated voltage, a motor produces only 81 percent of normal power and a lamp produces only 70 percent of its normal light.

Fig. 4-2 : Circuit showing voltage drop—voltage at motor is lower than at starting point.

In the example shown in Fig. 4-2, if 200 feet of 14 AWG wire is used, the drop is from 120 to 112 volts, or 8 volts, about 7 percent. If 12 AWG wire had been used, the drop would have been reduced about 60 percent to 3.2 volts, only about 2.5 percent of the starting voltage. The larger the wire, the less the voltage drop.

Voltage drop can’t be reduced to zero, but it can be kept at a practical level by using wire of sufficient size. A drop of 2 percent is considered acceptable. If the starting point is 120 volts, 2 percent is 2.4 volts, so the actual voltage at the point where the power is consumed is 117.6 volts. If the starting point is 240 volts, the voltage at the point of consumption is 235.2 volts. The apparent saving in initial cost by using undersize wire is soon offset by the cost of power wasted in the wires and by the reduction in efficiency of lamps, motors, and so on.

Table 4-1: AMPACITYOF WIRES (Based on NEC Table 310.16)

Not more than three current-carrying conductors in conduits or other raceways, or in cable assemblies or directly buried in the earth.

Selecting wire size Choose a type and size of wire that has an ampacity rating at least equal to the expected load (in amperes) and that is large enough to limit voltage drop to a practical range. The NEC permits nothing smaller than 14 AWG for ordinary wiring. It’s better to consider 12 AWG the smallest, as this is required in a few places by local ordinance. Larger size wires may be required to minimize voltage drop in long runs, or to allow larger motors to start. If you need wire heavier than the minimum permitted, it’s somewhat complicated to figure the right size but simple to look it up in tables. First determine the amperage to be carried by the wire. Most appliances will have a nameplate giving the total amperes or watts rating.

Tables 4-2 and 4-3 show one-way distances in feet for 2 percent, voltage drop at 120 and 240 volts. These are recommendations in NEC 210. 19(A)( 1) FPN No.4 and 215.2(A) (4) FPN No.2. Use the table that corresponds to the voltage of the circuit question. To operate a load 300 feet away requires 600 feet of wire, but look for/the figure 300 in the table. The distances under each wire size are the distances t size wire will carry the different amperages (or wattages) in the left- hand column with the customary 2 percent voltage drop. In the 120-volt table, to determine how far 8 AWG wire will carry 20 amps, follow the 20-amp line until you come the 8 AWG column : the answer is 90 feet. If a distance is marked with an asterisk (*), it indicates that Type TW wire in conduit or cable, or a cable buried directly in\the ground, may not be used because the amperage in the left-hand column is eater than the ampacity of Type TW. Select the proper type of wire from Table 4-1, or from Table 310.16 in the NEC.

Compare the 120-volt and 240-volt tables. Note that at 240 volts, any given size of wire will carry the same amperage twice as far as at 120 volts with the same percentage of voltage drop. It will carry the same number of watts four times as far.

When wires are run outdoors overhead, they must be large enough to carry the amperage involved without excessive voltage drop. They must also be large enough to support their own weight. NEC 225.6(A) requires a minimum of 10 AWG for spans up to 50 feet and 8 AWG for larger distances. For distances over 150 feet, it’s wise to use an extra pole. In northern areas where the wires often must support a heavy ice load, consider using a size larger than electrically required. If the wire is installed on a hot summer day, leave considerable slack; otherwise the contraction of the wires in winter may pull the insulators off your buildings.

Weatherproof wire has a covering of neoprene or impregnated cotton over the conductor. The NEC calls it “covered”—the covering is not recognized as insulation. Weatherproof wire must not be used for ordinary wiring, but only for over head wiring outdoors. Although its ampacity is higher than that shown in Table 4-1 because it runs in free air, any equipment connected at its terminations falls under the general rules, resulting in the use of Columns A and B as a practical matter. Using the higher ampacities involves a level of engineering sophistication not assumed for the users of this book. In addition, don’t forget that smaller wires lead to higher voltage drop.

Table 4-2 One-Way Distances for 2% Voltage Drop by Wire Size at 120 Volts Single-Phase

In the tables above and below, the figures represent one-way distances in feet, not the total wire length for two-way distances.

* In both tables, for distances marked with an asterisk (*) Type TW wires in conduit or cable may not be used because they don’t have enough ampacity. For all distances marked with the asterisk, select a type of wire with sufficient ampacity (depending on whether in conduit or cable, or in free air) from Table 4-1.

If you wish to permit 4% drop, double the distances shown. Multiply the distances by 2.5 to permit 5% drop.

Table 4-3 one-way distances for 2% voltage drop by wire size at 240 volts single-phase


Wire of the correct type as well as of the correct size must be used to assure a safe installation. Wires covered with various types of insulation are used for wiring the interiors of buildings. (Wires for outdoor installations are discussed in the Section on farm wiring.) Wire names indicate the type of insulation, and these names are generally abbreviated.

The different colors of wires indicate function. The special uses of white and green wires are summarized elsewhere in our discussion. Black wires are “hot” (energized)—they carry current to electrical equipment. Red and blue, if used, are also hot; use of such additional colors makes it easier to tell wires apart in a complicated installation. Number 4 AWG and larger wires are usually available only in black, and weatherproof wire in all sizes is always black.

Number 10 AWG and smaller wire is usually solid—the copper conductor is a single solid strand. Number 8 AWG maybe solid if it’s in the form of cable or is not to be drawn into conduit a installation. But 8 AWG that is to be drawn into conduit must be stranded—several smaller wires are grouped together to make one larger wire (see Fig. 4-1 is more flexible. Wire that is 6 AWG or larger (with the exception of we wire) must always be stranded.

To protect wire from damage they are pulled into pipe called conduit or are used in the form of multi-conductor cables. In addition to the wires described in this book, many other types are available, but they are usually not used in residential and farm wiring. You will find them listed in your copy of the NEC.

Fig. 4-3 : Type TW is seldom used today, having been largely replaced by dual-rated THHN/ THWN, which uses the same insulating compound, but in a much thinner layer overlaid by a tough outer layer of clear nylon that provides excellent mechanical protection. It may be used in wet or dry locations. Number 6 AWG or larger must be stranded, and 8 AWG must be stranded if pulled into conduit.

Types TW and THW wire: The most commonly used wire is thermoplastic insulated. The conductor is covered by a single layer of plastic compound, the thickness of which depends on the size of the wire, and which strips off easily and cleanly. See Fig. 4-3. Type TW is moisture-resistant and suitable for use in wet locations. Type THW is resistant to both heat and moisture. Neither TW nor THW maybe buried directly in the ground.

Type R wire: Formerly rubber-covered, this kind of wire has a synthetic polymer insulation, and it may have a moisture-resistant, flame-retardant outer covering of neoprene or PVC. Figure 4-4 shows the makeup of the original Type R conductor. Once the most popular of all kinds of wire, Type R is no longer used today, and has been removed from the NEC. However the more modern higher-temperature versions, RHH (90°C) for dry and damp locations, and RFIW (75°C) and RHW-2 (90°C) for dry or wet locations, are still used.

Fig. 4-4: Rubber-covered wire has rubber instead of plastic insulation, and it may have a fabric or other nonmetallic flame-retardant outer covering.

Aluminum wire : This is available in two types—aluminum and copper-clad aluminum (aluminum with a thin sheath of copper on the outside). Because aluminum is not quite as good a conductor, a larger size must be used than when using copper. A rule of thumb is to use aluminum two numbers heavier than copper : 12 AWG aluminum instead of 14 AWG copper; 4 AWG aluminum instead of 6 AWG copper, etc.

When aluminum wire was first used, it was connected to ordinary terminals that were suitable for copper, but it soon became evident they were not suitable for aluminum. The connections heated badly and led to loose connections, excessive heating, and sometimes fires. The product standards were revised, and test labs then required redesigned terminals, marked AL-CU, that were considered suitable for either copper or aluminum, but in the 15-amp and 20-amp ratings they were still not suitable for aluminum. The terminals were further redesigned and since 1971 only devices with the marking CO/ALR are acceptable. Note that terminals rated higher than 20 amps were not changed, so those marked AL-CU are still acceptable and they must be used when aluminum wire is installed.

The AL-CU or CO/ALR marks are stamped into the mounting yokes of switches, receptacles, and similar devices in order to remain visible without removal from the boxes in which they are installed. On larger equipment the marks are located so they remain visible after installation.

If your existing installation was made using aluminum, you would be wise to inspect all your receptacles and switches. If they are not marked CO/ALR, replace them all with devices that do have the mark, or reconnect them with copper pigtails. (Replacement instructions are discussed elsewhere.)

Keep in mind that if the aluminum wire is copper-clad, any kind of terminal may be used. Push-in terminals, shown in Fig. 4-16, may be used with copper or copper-clad aluminum, but not with ordinary aluminum.


Wires are often assembled into cables such as nonmetallic-sheathed cable or armored cable. When a cable contains two 14 AWG wires, it’s known as 14-2 (four teen-two) cable; if it has three 12 AWG wires, it’s called 12-3, and soon. If a cable has, For example, twIl4 AWG insulated wires and a bare uninsulated grounding wire, it’s known as 14-2 with ground?’ If a cable has two insulated wires, one is always white and on black; if it contains three, the third is red.

Nonmetallic-sheath cable : This is a very common type of cable containing two or three Type THi-IN or THHW wires. Many people call it “Romex’ which is the trade name of one particular manufacturer. It’s easy to install, neat and clean in appearance, and less expensive than other kinds of cable. Brief descriptions of the two kinds follow here. See Section 11 for a complete discussion of where and how to use nonmetallic-sheathed cable.

One kind of nonmetallic-sheathed cable is called Type NM by the NEC. As shown in Fig. 4-5A, the individually insulated wires are enclosed in an overall plastic jacket. (In older construction, occasionally still seen, the outer jacket was a braided fabric. In any case, the outer jacket must be moisture-resistant and flame-retardant.) Some manufacturers put paper wraps on the individual wires or over the assembly. Empty spaces between wires are sometimes filled with jute or similar cord. This type may be used only in normally dry locations, but never in barns on farms.

The other kind is called Type NMC by the NEC and is especially designed for damp or corrosive locations such as barns. It may also be used in ordinary dry locations. The individual insulated wires in Type NMC cable are embedded in a solid sheath of plastic material (see Fig. 4-5B). Sometimes there is a glass overwrap on each insulated wire. There is no fibrous material such as paper wraps or jute filler that can be affected by moisture as in ordinary Type NM .

Fig. 4-5A Nonmetallic-sheathed cable consists of two or more individual wires assembled into a cable. The Type NM two-wire with ground shown here may be used only in dry locations.

Paper wrap required on ground wire; overwrap under the outer jacket optional if additional testing requirements met. Bare equipment grounding conductor. V Flame-retardant plastic outer sheath.

Fig. 4-5B Nonmetallic-sheathed cable, Type NMC, may be used in dry or damp locations.

Armored cable NEC Type AC ( Fig. 4-6) is called “BX” by many people although that is the trademark of one particular manufacturer. The individual wires may be type TW, THW, or THHN. There may be an overwrap of tough paper between the wires and the spiral steel armor. Where installed in thermal insulation, the conductors are required to be rated 90°C but with 60°C ampacity (making it unnecessary to go through the math for de-rating for high ambient temperature as required at the bottom of NEC Table 310.16). It’s for use only in permanently dry locations. Details for using armored cable are provided in Section 11.

Fig. 4-6: Armored cable consists of two or more individual wires assembled into a cable and protected by flexible steel armor. It may be used only in dry locations.

Underground cable : Two special types of cable, USE and UF, are used for under ground wiring. They are described in the Section on farm wiring.


Flexible cords are used to connect lamps, appliances, and other loads to outlets. Each wire consists of many strands of fine wire for flexibility. Over the wire is a wrapping of cotton to prevent the insulation from sticking to the copper. There are many kinds of flexible cords with varying kinds and thicknesses of insulation depending on the purpose of the cord. The more common kinds are described here.

Type SPT-2 is the most common cord used for radios, floor lamps, and similar loads. As shown in Fig. 4-7, it consists of copper wires embedded directly in plastic insulation. It’s tough, durable, and available in various colors. The same kind of cord with a rubber-like insulation is known as Type SP-2. These cords are commonly available only in 18 AWG and 16 AWG.

Type S, in Fig. 4-8, is a really durable cord that stands up to hard use. Each wire has rubber or plastic insulation. The two wires are bundled into a round assembly with jute or paper twine filling the empty spaces. Over all is a layer of tough, high-grade, rubber-like plastic. Type SJ is similar but with a thinner outer layer. Type SV or SVT are very similar but more flexible cords used on vacuum cleaners.

If the outer jacket is made of oil-resistant thermoset plastic, the cord becomes oil- resistant and the designations become SO and SJO instead of S and SJ.

“Heater cord” is used for irons, toasters, and other heating appliances. Heater cords formerly had asbestos under a cotton braid as part of the insulation system. Asbestos is no longer used as wire insulation. Figure 4—9 shows Type HPN heater cord; the wires are embedded in neoprene.

Fig. 4-8: Types Sand SJ cords are designed for very heavy use.

Fig. 4-9: Type HPN cord is used on irons, toasters, and other heating appliances.


Tools needed for carrying out various electrical jobs are mentioned in the text where the procedures are described. The tools listed below are commonly used in wiring procedures.

- Cable cutter for cutting armored cable

- Cable ripper for removing the outer jacket from nonmetallic-sheathed cable Conduit bender for bending conduit

- Hacksaw for cutting armored cable, EMT, and openings in existing walls

- Putty knife sharpened to lift floorboards to get at ceiling spaces from above

- Keyhole saw for cutting floorboards

- Fish tape for pulling wires into place

- Parallel-jaw pliers for use with connectors

- Pliers with crimping die for use with connectors

- Side-cutting pliers for removing insulation from wire

- Wire stripper or knife for removing insulation from wire

- Test light for receptacles and fuses

- Continuity tester for testing that hot wires in switches are not accidentally grounded and for detecting broken wires in cords


Various kinds of terminals provide the means for connecting wires to devices. Before wires can be connected to a device or spliced to another piece of wire, the insulation must be removed. The procedure begins with preparing the wire.

Removing insulation from wire : Using a tool called a wire stripper is the most convenient way to remove insulation from wire. Another method is to use a pair of side-cutting pliers. Insert the wire close behind the hinge of the plier blades and mash the insulation, softening it, from the point where it’s to he removed to the end. Then place the jaws of the pliers at the point where the removal is to begin, squeezing just hard enough to cut into the insulation without touching the conductor; the mashed insulation can then he pulled off easily.

If you don’t have a wire stripper or side—cutting pliers, you can use a knife. Don’t cut the insulation off sharply, as shown at A of Fig. 4-10, because it’s too easy to accidentally nick the conductor, leading to later breaks. Hold your knife to produce an angle as shown in B of Fig. 4-10.

Fig. 4-10 : Wrong and right methods of removing insulation from wires.

Always make sure the stripped end of wire is absolutely clean. Rubber-covered wires have a tinned conductor to make it easy to strip off the insulation. Plastic-insulated wires-are not tinned because that kind of insulation strips off cleanly.

Fig. 4-11 : Terminal on a typical receptacle or switch.

Fig. 4-12 : Solderless connectors of this type are used with heavy sizes of wire.

Two types of terminals : There are two kinds of terminals. One kind consists of a terminal screw in a metal part with upturned lugs to keep the wire from slip ping out from under the screw, as shown in Fig. 4-11. It may be used with 10 AWG and smaller wires, but it’s very difficult to make a good connection if the wire is 10 AWG and stranded. The other kind is used mostly for wires larger than 10 AWG; the wires are inserted into the terminal of a solderless connector and the screw is then tightened. See Fig. 4-12.

The correct method for terminals for to AWG and smaller wires is shown in Fig. 4-13. Wrap the wire at least two-thirds (preferably three-quarters) of the way around the screw in a clockwise direction so that tightening the seresv tends to close the loop rather than open it. Tighten the screw until it makes contact with the wire, then tighten it about another half-turn to squeeze the wire a bit. As an alternative, tighten the screws to the pound-inches marked on the product, or to 12 pound-inches as recommended in Fig. 4-13. Never make the errors shown in Fig. 4-14. The insulation should end not more than ¼ inch from the screw at the most. Note that these two illustrations were made specifically for aluminum wire, hut the principles are also correct for copper wire.

Fig. 4-13 : Be sure wire is wrapped around terminal screw in clockwise fashion as in Step 1 so that tightening the screw tends to close the loop. Then complete Steps 2 and 3. (UL Inc.)

Fig. 4-14 : Avoid these common errors when connecting wire to terminal screws. (UL Inc.)

Fig. 4-15 : Use this method, commonly called a “pigtail” splice, when you would otherwise have to connect two wires under a terminal screw.

Don’t connect two wires under a single wraparound terminal screw even though it might appear logical in some situations. The NEC prohibits it in 110.14(A). Take those two wires and another short length of the same wire, and connect all three together using a wire connector described later in this Section. See Fig. 4-15. Then connect the remaining end of the short wire under the terminal screw. Most connectors of the kind shown in Fig. 4-12 are for one wire unless the connector is marked to indicate the number and size of wires that can be accommodated. The marking may be on the carton if the connector itself is too small for the marking.

What length should the bare wire be for connecting it under the terminal screw? Professionals leave about 3 inches of hare wire, enough to leave a “tail” beyond the tightened screw Twist this tail a few times and it will break off near the screw. Another way is to leave just enough bare wire to go around the screw, form a loop with a pair of long-nose pliers, slip it around the screw, close it with the pliers so that the loop is entirely under the screw, and then tighten the screw.

Push-in clamps : Many 15-amp and 20-amp receptacles and switches have no terminal screws at all. Instead, there are internal terminal clamps that grasp a straight piece of wire pushed into them, forming an effective connection. Merely strip the end of the wire for half an inch or so (the proper length is usually shown on the device itself), and push the wire into the hole on the device. See Fig. 4-16. If an error is made, release the clamp by pushing a small screwdriver blade into another opening on the device. These push-in connections are acceptable only for copper or copper-clad aluminum wire. They must not be used with all-aluminum wire. For receptacles these connections are limited to 14 AWG wire.

Fig. 4-16 : Strip the wire, push it into opening on switch or receptacle, and the connection is made.

Fig. 4-17 : In raceway wiring, a continuous wire may be connected to a terminal as shown here.

Connecting wires from raceway : In raceway wiring, sometimes a wire is pulled through one box and on to another, possibly through still another, and so on. If the wire merely runs through the box, pull it through without splice hut leave a loop in case it’s necessary to re-pull it in the future. If you intend to make a connection to the wire as it passes through the box, let a loop several inches long project out of the box. Strip away an inch or SO of insulation, form a loop, and connect it under one terminal screw as shown in Fig. 4-17.


Connectors are used in splicing (joining) two or more pieces of wire together. It’s important that whichever type of wire connector you use, you are certain it’s listed for the number and size of wires that are to be joined. The spliced wires must he electrically as good as an unbroken length of wire. The insulation of the splice must he as good as that on the original wires. Such a splice is accomplished by using properly installed insulated solderless connectors. Many people call these “Wire Nuts,” which is the trade name of a particular manufacturer. When two or more ends of wire must be connected to each other, lay the wires together with their cut ends pointing in the same direction; insert the wires into the connector and turn it onto the wires, which twists them together as shown at the right in Fig. 4-18.

Fig. 4-18: Two types of solderless connectors for smaller wires, often called by the trade name “Wire Nut.” The version with the setscrew maintains the integrity of the electrical connection even with the insulating cap removed. This makes it a good choice if the connection will be tested with diagnostic equipment while energized, such as with some motor connections.

Connectors for joining two or more wire ends : One type of connector has a threaded metal insert molded into the insulating shell. Screw the connector onto the wires to be joined. The other kind has a removable metal insert. Slip the insert over the wires to he joined, tighten the screw of the insert, and then screw the insulating shell over the metal insert.

Fig. 4-19: This kind of connector contains a tapered coil spring inside the insulating cover.

The spring-loaded connector shown in Fig. 4-19 is also popular. Inside its insulating shell there is a cone-shaped metal spring. Screw the connector over the wires to he joined. The insulating cover provides a good grip. When being screwed on, the coil spring temporarily unwraps. When released, it forms a very tight grip on the wire.

In using these connectors, if one wire is much smaller than the others, let it project a bit beyond the heavier wires. If you have removed the right length of insulation from each wire, the insulating shell will cover all bare wires and no taping is necessary. Note that all types of these connectors arc available in various sizes, depending on the number and size of the wires to be joined. Take care to observe the restrictions on allowable wire combinations that come with these connectors.

For wire sizes 0 AWG and smaller, the insulated “clamshell” connector shown in

Fig. 4-20 may be used. The wire insulation is used to position the wire in this type of connector, so don’t strip the wire insulation before installing in the connector. A squeeze with parallel-jaw pliers installs the self-insulating connector.

Fig. 4-20: “Clamshell” wire connector for taps or pigtails. For copper wire only.

Another wire connector, for 10 AWG and smaller wire, is the shell shown in Fig. 4-21. Unless the manufacturer’s instructions direct otherwise, first twist the wires together, then slip the shell over them and crimp using a tool of the type shown. Then cut off the wire ends that could puncture the insulation, and either tape or use formed plastic caps to insulate.

Fig. 4-21 Crimp-type wire connector, and pliers with special crimping die in handle. For copper wire only.

Fig. 4-22 For heavier wires, use metal connectors. The assembled connector and wires must be taped.

For wires that are too large to be joined by the connectors described above, use heavy duty copper connectors of the style shown in Fig. 4-22 or Fig. 4-23.

Connectors for splicing to a continuous wire Sometimes a wire must be spliced to another continuous wire. In the heavier sizes, the simplest way is to use one of the split-bolt connectors shown in Fig. 4-23. Tape after making the connection. Some connectors are available with an insulating cover that can be snapped on after making the connection. For smaller sizes, it’s usually simpler to cut the continuous wire to form two ends; the wire to be spliced in the connection makes the third wire. Then use a solderless connector as shown in Fig. 4-15.

Fig. 4-23 Use this split-bolt connector when splicing a heavy wire to another continuous heavy wire. The assembled connector and wires must be taped.

Insulating splices Splicing devices such as solderless connectors are self- insulating. For other styles, insulating covers or boots are available that can be added after the splice is made. Some must be taped (see Figs. 4-22 and 4-23). Use electrician’s plastic tape--it has a very high insulating value despite its thinness. Starting well back on the wire insulation, wrap the tape on spirally from one end to the other, partially overlapping each turn, and then return with the spiral in the opposite direction. If the splice will be subject to mechanical strain or abuse, apply additional layers as a cushion.

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