Getting Wired

By David Herres

Addressable fire alarm head allows for exact location displayed at the control panel.

Many may remember when the telephone company owned phones and associated wiring in our homes. Initial installation, alterations and repairs were performed by utility personnel, who provided equipment, materials and expertise. Eventually this arrangement fell apart and the work went up for grabs. Traditional light and power electricians moved in to fill the gap. They had no problem acquiring the technology and found they could step up to large commercial work with a little research and on-the-job experience. They took on a good portion of the work and a new class of communication technicians emerged.

Today, statistics show there is a growing shortage of electricians at a time when our electrical infrastructure needs lots of work, Moreover, new construction is bound to grow, once we get through this construction trough. Many tech-minded young people want to program computers or design Websites rather than run cable, but that could soon change, especially as contractors seek to broaden their service and installation offerings.

Code mandates

New Code mandates mean additional sprinkler and fire alarm work are on the horizon.

The Internet is everywhere. Satellite dish and cable hookups to several rooms in every house results in a demand for Ethernet or wireless know-how. On a commercial level, this can involve telecom rooms and substantial cabling. In an industrial setting, there is everything from Class 2 wiring for motorized valves to PLC technology.

Security and surveillance cameras, often with Power over Ethernet, are there for those who feel the calling. In recent years there has been a great proliferation of second homes, many in fairly remote areas, where burglar and low temperature alarms with remote notification have become hot items.

Each of these areas demands a certain level of expertise. A large fraction of this equipment has a 10- to 20-year service life and new technologies become available. which provides more work.

It's always a good approach is to run metal raceway even where not required, such as outside of classified (hazardous) areas. Then, at some point in the future, today's Cat 5e UTP cable can be used to pull tomorrow's optical fiber to satisfy the ever-increasing appetite for bandwidth.

This wiring is loosely called "low voltage," but that is a bit of a misnomer. National Electrical Code Article 725, which covers many of these installations, allows up to 600V in Class 1 circuits.

This article, which appears in NEC Chapter 7, Special Conditions, can be a little baffling if you have been doing traditional house wiring, but it becomes clear if you give up the idea of a hierarchy of classes based on voltage or power levels. Instead they are based on degree of protection required. Class 1, requiring the most protection, is so designated because of either of two conditions:

Remote-control circuits for safety control equipment are Class1 if failure of the equipment to operate introduces a direct fire or life hazard. Thermostats and similar circuits for heating and cooling do not fall into this category. Neither does fire alarm wiring because this equipment reports a hazard but does not introduce it. The voltage is up to and including 600V and the power is unlimited. Where circuits are designated Class 1 because of the safety issue, the conductors must be "MC or better." This is shorthand for the following types of protection: rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, electrical metallic tubing, type MI cable or type MC cable. Type NM (trade name Romex, as used in residential and some commercial construction) is out.

Class 1 wiring where so designated due to voltage and power levels, is permitted to employ Class 3 (i.e. conventional) wiring methods and materials if they are appropriate to the setting.

Class 2 and Class 3 wiring are so designated because of voltage and power levels of the source. The limitations are given in Tables 11(A) and 11(B) in NEC Chapter 9 and are fairly complex because the current and power limitations vary with different voltage levels within each class. Fortunately, the electrician does not often get involved in this matter since the circuit class is printed on the listed transformer or circuit card. A dry cell battery is considered Class 2 if it is not over 30V and the capacity is equal to or less than that available from series connected No. 6 carbon zinc cells.

Thermocouples are Class 2 and are not required to be listed.

Class 2 circuits are considered inherently safe from a point of view of shock and fire initiation. Wiring methods are generally more lenient than other types of wiring. Class 3 circuits, with higher voltage and power limits, are still considered safe from a fire initiation perspective but may present a shock hazard. The wiring methods are more stringent.

Class 3 is less frequently encountered; Class 2 generally will be the focus. Other types of low voltage wiring are covered in the rest of NEC Chapter 7 and Chapter 8, Communication Circuits. Of particular importance are:

• Article 720: Circuits and Equipment Operating at Less than 50V.
• Article 760: Fire Alarm Systems.
• Article 770: Optical Fiber Cable and Raceways.
• Article 780: Closed Loop and Programmed Power Distribution.
• Article 810: Radio and Television Equipment.
• Article 820: Community Antenna Television and Radio Distribution Systems.
• Article 830: Network-Powered Broadband Communication Systems. These articles delineate the basic varieties of low voltage cabling and requirements for a safe installation. While they won't tell you how to pin out various kinds of Ethernet connections, they will provide guidance for choosing the right cable for the environment involved.

As mentioned earlier, most of this wiring does not present a fire initiation hazard. However there is an acute fire propagation potential, which must be addressed in every installation. Whereas the voltage and power levels of power-limited circuits are not enough to ignite combustible material even in the event of a short circuit, nevertheless it must be recognized that the insulation on this cabling Ñ if ignited by a fire emanating from some other source Ñ is capable of generating a huge amount of toxic smoke. The degree of hazard depends upon, among other factors, the amount and placement of this cabling. This is why NEC has jurisdiction over power-limited circuits.

It is mandated that accessible abandoned wiring is to be removed. This requirement does not apply to power and light wiring, just low voltage cabling.

Conductors that have been installed in raceway are not considered accessible, so they may stay. However anything over a suspended ceiling is accessible (though not readily accessible) and has to be removed. Abandoned is precisely defined over and over in the low voltage articles as cable that is not terminated at equipment and not identified for future use with a tag.

It is proper that this material should be removed, but who is responsible for getting the job done? In commercial occupancies, new tenants frequently move in with entirely new data and voice requirements and as a result the installations are reworked. Many buildings are encumbered with a vast amount of old cable that has not been removed. For the electrical contractor, it is important to understand whether abandoned cable removal is within the scope of a contemplated job.

Another recurrent theme in NEC low voltage cabling articles is the hierarchy of installation environments: The higher on the list, the more sensitive is the location in regard to fire propagation and smoke generation. Listed plenum cable must be used in a plenum location since it has more favorable characteristics. It is also much more expensive. Riser is in the middle and general purpose is for less sensitive locations and less expensive. You can substitute a cable higher on the list for a cable lower on the list. For small jobs, it may make sense to keep only plenum cable and use it for everything.

Another NEC requirement for all low voltage work is that it be performed in a neat and workmanlike manner. Cables must be supported adequately to prevent damage. It is also emphasized within each article that access to electrical equipment must not be denied by an accumulation of cabling that prevents removal of panels, including suspended ceiling panels.
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