During tough economic times, it’s important to maximize productivity: spend less money to accomplish more work. Manufacturers are betting that supplying prewired components and modular assemblies will do just that for contractors. There are a number of different approaches; the first thing to look at is whether we’re talking about power, control, data or communications work.
Contractors these days often are called to install infrastructure for controlling and integrating systems. Structured cabling makes that job easier and ensures that the end product is a system that will work well in a variety of conditions. Designed to transfer high-speed digital data, the type of cable, its length and installation are crucial for proper functioning.
The heart of a structured system is a central patch panel. Cables are run from jacks at users’ terminals back to the patch panel, and from that to the various signal sources. Each cable is numbered and identified by its type and ratings, e.g., Category 5 or 6. By changing jumper cables at the panel, any source that can operate over that cable can be connected to any terminal. If, for example, the CEO wants to see video from a security camera at the front door, only the jumper cable has to be changed.
Prewired structured cabling systems cover a space or an entire building with low-voltage cable in an ordered arrangement that is tested, labeled and recorded. An important feature of the system is that every cable run has been described, tested and the results stored, so it is clear what they can and cannot be used for. If a run of communications cable has to be upgraded for higher bandwidth, the old cable might still be used for lighting or heating, ventilating or air conditioning control signals. When a system is upgraded, the old installed ca-bling will be put to a new use.
Communications Integrators Inc. (Cii), Tempe, Ariz., manufactures power and data distribution systems to customer specs. Assembled and tested at the Cii factory, the systems are ready to fit in place at the site. Power wiring is run directly from the user’s closet through home run cables to a power distribution module (PDM). Each home run can hold 10 to 12 wires, and two such cables can tie into the PDM, which can feed up to 24 120-volt circuits, providing evenly balanced loads for the three-phase input power. Each 120-volt circuit is then daisy chained to locations throughout the space. The cables are run in super flex conduit and are fitted with connectors at each end, which can be hot connected and disconnected, making it especially easy to modify in the field.
ACS/Uni-Fab, New Bedford, Mass., makes prewired lighting cables in standard sections that are used to connect a string of lighting fixtures by means of pigtails and connectors.
Products such as prewired raceway, assembled by a manufacturer to a user’s specs, can provide ready-to-install sections of power and data cabling that plug into each other end-to-end.
See the prewired raceway from Wiremold/Legrand (www.wiremold.com). To get the correct system, the installer has to provide a complete set of drawings based on Wiremold’s mechanical specifications. These need to include specs for power and communications wiring; barriers between the two; and choice, location and size of connectors and receptacles.
Pass and Seymour/Legrand (www.passandseymour.com) provides prewired receptacles connected to wall or floor mounting brackets.
Modular panelboards for power distribution are becoming more available. Schneider Electric has a line of lighting panelboards, Square D NQ, which have modular kit-like features. Parts can be easily assembled or even replaced in the field with ready-to-install subassembly kits including subfeed circuit breakers, TVSS interiors, 200 percent neutrals and box extension kits.
Motor control centers
The traditional approach for controlling motors has been to use a separate piece of switchgear and combination starter for each mo-tor, or several starters could be combined in a single motor control center (MCC). Manufacturers, such as Siemens and Rockwell Automation, now offer modular MCCs with built-in intelligence and communication capabilities. The modularity of this kind of system not only simplifies the initial installation, but it also simplifies field modification to accommodate future load changes.
Manufacturers are delivering quite a range of modular and prewired systems, which reduce installation time and may cut down on callbacks and excess maintenance. These are ideal for commercial, industrial, health and hospitality settings, which require power and data to be widely distributed and are subject to frequent modifications during the system’s life.
BROWN is an electrical engineer, technical writer and editor. For many years, he designed high-power electronics systems for industry, research laboratories and government. Reach him at firstname.lastname@example.org or at www.writingengineer.com, an independent professional writing service.