Wiring methods

Materials for wiring interior electrical systems in buildings vary depending on:

• Intended use and amount of power demand on the circuit
• Type of occupancy and size of the building
• National and local regulations
• Environment in which the wiring must operate.

Wiring systems in a single family home or duplex, for example, are simple, with relatively low power requirements, infrequent changes to the building structure and layout, usually with dry, moderate temperature, and noncorrosive environmental conditions. In a light commercial environment, more frequent wiring changes can be expected, large apparatus may be installed, and special conditions of heat or moisture may apply. Heavy industries have more demanding wiring requirements, such as very large currents and higher voltages, frequent changes of equipment layout, corrosive, or wet or explosive atmospheres. In facilities that handle flammable gases or liquids, special rules may govern the installation and wiring of electrical equipment in hazardous areas.

BASIC PRINCIPLES OF GOOD WIRING

• Before beginning any electrical repair, shut off the power. Remove the fuse or trip the breaker for the circuit you will be working on in your service panel. Use a neon tester to be sure the power is off. If there is any doubt, you can remove the main fuse or trip the main breaker. Remember: Removing the main fuse or tripping the main breaker will usually shut off the power to the entire house.
• Electrical wires are color coded to prevent wiring errors.
• White wires almost always connect to other white wires or to chrome terminal screws on switches and receptacles.
• Some wiring devices–such as receptacles–are back-wired by pushing the bare wire end into spring grip holes. These wiring devices are plainly labeled to show which color goes into each spring grip hole.
• Switches are nearly always connected into black wires in cables. The only exception is where a cable is extended, making it necessary for the white wire to play the role of the black wire. When this is necessary, the white wires should be painted black to prevent future wiring errors.
• Study the wiring diagram. This will help you understand the basic principles of good wiring. Also, find a good electrical how-to book. It's one book every homeowner should keep on hand for ready reference.
• Most home wiring is complete with either No. 14 gauge or No. 12 gauge wiring. No. 14 is the smallest wiring permitted under most codes.
• Always use the same size cable for a continuation of any extended wiring circuit

Data And Power Wiring: Similarities & Differences

The industry is instinctually familiar with power wiring. Now, it's time for electrical contractors to learn as much about data wiring as they already know about power wiring.

It's no secret data wiring is nearly as important to the electrical construction industry as power wiring. While the datacom market is a great boon to electrical contractors, it's also brought a bit of a problem: Most understand power wiring almost instinctually, however, the industry has no similar base for data wiring. Sure, it's not too difficult to follow wiring diagrams and specifications, but most contractors don't understand the fundamental issues of data wiring.

You should understand data wiring the same way you understand power wiring; but of course, you must first master most of the electrical basics (Ohm's law, series, and parallel circuits, etc.). Then, you can easily obtain a fundamental understanding of data wiring. Covering copper data wiring only, the following can help you begin developing a gut-level understanding.

A common concern — the amount of power. When installing power wiring, the amount of power installers feed to the outlet is a primary consideration. Wishing to avoid overcurrent (too much power), they also want to avoid excessive voltage drop (too little power). You should have similar concerns with data cabling. If not enough signal passes from one end of the cable to the other, you can't read the data, and the transmission becomes useless.

Since all datacom circuits have limited power levels, don't worry about too much current flowing to the datacom devices. However, do be concerned with too little current.

As a signal propagates down a length of data cable, it loses some of its energy. Therefore, a signal that starts out with a certain level of voltage arrives at the load with a reduced-voltage level. The amount of signal loss is attenuation, measured in decibels (dB).

If the voltage of a datacom signal drops too much, the signal will no longer register at the other end of the line. Then, the transmission is useless. This is the same thing as voltage drop; it's a loss of power.

The datacom concern — quality of signal. With power wiring, most installers are not usually concerned with the quality of the sine wave running through the conductors. Power companies keep their power as close to 60 Hz as they can, and voltage rarely varies from within preset limits. When troubleshooting a malfunctioning light fixture, the shape of the sine wave is not an immediate concern.

With datacom work, the quality of the signal is a primary concern. The readability of a data transmission depends on very careful timing and properly shaped pulses of electricity.

The figure (in original article) shows what can happen to data signals. At the left of the drawing is a clean square-wave signal entering a data cable. Each segment of the signal represents either a zero (a lack of voltage) or a one (the presence of voltage). The signal pulses coming out at the right end of the long cable have spread out noticeably. When this happens, the electronic communication circuits can't distinguish between a zero and a one, making the signal useless.

This pulse spreading isn't a loss of power. A 5V signal enters the cable, and a 5V signal exits the cable; but the shape of the signal is vastly different. This drastically affects its usefulness.

Here are two concerns for data transmission:

• Losing too much power (attenuation), and

• Not maintaining the quality of the signal (distortion).

Both are critical concerns, and either can disrupt a data transmission. The distortion of a data signal is generally due to either the excessive inductance (including inductance between circuits, also known as crosstalk) or capacitance of a data cable.

Installation. Like power wiring, the installation of data cabling consists of two primary phases, roughing in the wiring and trimming it later.

During the rough-in phase, remember to install all the cables in the proper places, taking care not to bend too tightly, pull too hard, skin, or otherwise damage the cables. Consider the routing of the cables, especially if they are unshielded.

Never place unshielded-copper cables too closely to sources of electromagnetism, such as motor windings, transformers, ballasts, or the like. Note where the fire barriers are within the structure, making proper allowances for crossing them.

Roughing data cable differs from roughing-in power wiring when it comes to protection during the construction process. When it's a long time between the cable installation and installing the jacks, it's up to you to protect your cables. If you don't protect them, you may pull and twist them by accident, damaging the cables.

In other situations, such as when using a complete raceway system, you may have little time between the cable installation and wiring the jacks.

As with power wiring, it's important to leave enough extra cable at each outlet point. Recommended lengths are a minimum of 3 m in the telecommunications closet for twisted-pair and fiber cable, and 30 cm for twisted-pair cable at the outlet. (Notice when you move from power wiring to data cabling, the units of measurement switch from English to metric.) Remember to check your specifications for requirements on extra cable.

Trimming data cabling is much the same as trimming power wiring (strip the cables, install the devices and plates, etc.). However, when trimming power wiring, installers usually test it by flipping a switch or hitting the outlet with a Wiggy; power is either present, or it's not.

Testing data cabling is not so simple. Remember, you should test not only for the presence of the signal, but also for the quality of the signal. You should also spend more time testing your cables and documenting those test results. This is simply part of the datacom business; there's no avoiding it.