FOR COMMERCIAL ESTABLISHMENTS

SMALL COMMERCIAL OCCUPANCY

In planning the wiring system for a small commer­cial building - either from a design or installation standpoint - there are several factors to be considered before material is ordered and the actual installation takes place.

Some of the factors that should be considered for small commercial establishments include the following:

1. Type of general building construction.
2. Is the installation a part of a new building or a modernization of an existing one?
3. Type of ceiling, wall, and floor construction, dimensions, and the like.
4. Wiring methods.
5. Location of service, overhead or underground?
6. Location of service-entrance equipment.
7. Size of service and feeders and sizes and types of service-entrance equipment and panelboards.
8. Wiring of windows and display cases.
9. Type and installation requirements of lighting fixtures. Physical dimensions and construction of recessed lighting fixtures.
10. In the case of a modernization or complete wiring of an existing building, to what extent may the main service be used, and how much will it have to be enlarged?

Taking each of these individually, factor 1 may be determined by the working drawings and specifications, by a job-site investigation, or by consulting with the owners.

The wiring method to use may be dictated by the working drawings or specifications. If not, the wiring method to use should comply with the latest edition of the Philippine Electrical Code (PEC) and/or local ordinances.

The location of service equipment be indicated on the working drawings or the local power company may have to be consulted to determine the best location. Locating the service equipment is often left to the electrician or contractor to decide, but if working drawings are available, they should be followed.

Sizing the electric service requires calculations or the designer may have indicated the service size on the working drawings.

Lighting fixtures should be preselected by either the designer, owner, or architect. Installation details may be found in manufacturers' catalogs. Shop drawings are usually provided for commercial installations of any consequence.

In general, the designer or electrician performing the work will calculate the total load for the building, determine the number of branch circuits required and service-entrance size, along with feeders, service-entrance equipment, and panel boards. The number of outlets will be determined along with their location. Illumination levels are calculated and then lighting fixtures are selected to provide the required illumination.

Continue by noting connections for any special equipment, such as water heaters or air conditioners. Also determine the requirements for any secu­rity/ fire-alarm system, display case connections, and the like.

Determine the lengths of all branch circuits, service, and feeder runs and list the wire size for each. Account for service-entrance equipment and any other major pieces of equipment requiring electrical connections. Small commercial projects utilize rigid steel conduit for the service-entrance regardless of whether it is overhead or underground. Check with the local power company to find out exactly what is required of the contractor or electricians doing the work. Either rigid or EMT conduit is used for all wiring below grade and embedded in concrete slabs. Either EMT or type AC cable is normally used for wiring above grade.

One main point of concern with this type of project, as well as with most other electrical installations, is to plan the job well so as to perform the work in the shortest possible time, yet keep the quality high and in a workmanlike manner. Other trades should not be held up in performing their work, and the electrical workers must plan and work accordingly. For example, before the concrete floor may be poured and finished, all conduit, boxes, and fittings must be installed by the electricians. When the ground is graded, wire mesh installed, and the like, the electrical workers usually have only a certain amount of time to complete their portion of the work. Make certain all necessary material is at hand on the job site well before the installation will take place. Have the working drawings or at least a sketch at hand to go by, and work efficiently when the time comes. Also double-check each homerun, circuit, and outlet box location, as once the cement is poured, it would be quite costly to make any changes under it.

MEDIUM COMMERCIAL BUILDING

A medium-sized commercial occupancy is much planned, and there will be more circuits, a larger service entrance, etc.

Depending on the use of the building, the PEC or local ordinances may require a different wiring method than would be required in a smaller building.

Most larger commercial buildings utilize a 480/277-volt Y-connected service entrance; all heavy equipment, such as compressors for air conditioning, are designed for use on 480 volts; electric discharge lighting is all designed for operation on 277-volt, single-phase circuits; dry transformers are required to obtain 120 volts for convenience outlets; and other outlets use 240 and/or 120 volts.

Factors affecting wiring systems in large com­mercial buildings include the following:

1. Type of building construction, that is, masonry, reinforced concrete, wood frame, and the like.
2. Type of floor, ceiling, and partition construction, height of ceiling, space above ceiling, space under floor and the like.
3. Wiring methods, type of raceway, sizes of conductors.
4. Type of service-entrance equipment.
5. Type of service and location of service conductors.
6. Connections for equipment not furnished by the electrical contractor but requiring electric service.
7. Type and construction of lighting fixtures, hangers, and supports affecting assembly and installation. Types of lamps.
8. Type and dimensions of floodlighting supporting poles, floodlights and mounting brackets, and so on.
9. Ground conditions affecting trenching for parking lot lighting.

The majority of the factors can be determined by examining the working drawings and specifications, as any commercial building of this size will have a detailed, engineered set of drawings and specifications. If not, the contractor will have to have the system designed and working drawings made to aid the workers on the job. Building inspectors often also require that they be supplied with at least one set of drawings and specifications for use in their office and to check against the actual installation.

A complete take-off of materials will be required for this size of installation for the purpose of estimating the cost of construction, as well as for ordering material and scheduling it for use at the job site.

A better drawing, however, will have a complete power riser diagram to supplement the floor plan drawing, showing conduit sizes, wire sizes, number of conductors, and so on. The person installing the system, when only meager symbols are used, usually will have to make a rough layout of the installation and list all details before materials can be ordered or the installation started. Calculations will have to be performed to determine wire size, limit voltage drop, size of conduit, and the like. All these details should be worked out prior to starting the electrical installation.

Commercial electrical installations may vary considerably in detail. For example, each will have a service entrance, a distribution panelboard, lighting, and convenience outlets. Furthermore, nearly all will have emergency lighting and signal systems. All will have branch circuits, feeders, and the like.

When the electrical technician is called on to design or install a commercial electrical installation, there should really be no "strange" jobs once he or she has worked on a few commercial installations. Then, by following sound basic planning techniques and giving careful attention to details, the trained technician should never be completely stumped, even on jobs of a type that have not been previously handled. A certain amount of research will have to be done on all electrical jobs. Even seasoned professionals constantly refer to reference material for practically every new project. For example, while the professional engineer may remember the required footcandle level of, say, an office area, he or she will have to refer to manufacturers' catalogs to obtain the illuminating characteristics of certain lighting fixtures. Tables will be consulted to determine voltage drop on various sizes of wire over a given distance and carrying a certain load. Short-circuit calculations will be made to specify the required overcurrent protection -just to name a few. However, the pattern or sequence in which these unknowns are determined is practically the same on every commercial job.

Regardless of the technician's position - designer, electrician, supervisor, or whatever - a certain amount of planning is required on all commercial electrical installations. This planning is begun, before any work is started, and then continues on a day-to-day basis until the project is completed. Then a certain amount of planning is required to perform the final tests of the entire system.

Even on projects with detailed engineered drawings and specifications, planning and coordination during the construction phase are still necessary. Certain phases of the electrical installation will have to be carefully planned so as not to hold up any other trades from doing their work. Local inspectors will have to be notified at certain times so that they can inspect the work before it is covered up. Material and tools will have to be ordered so that they will be on the job site when needed. The design group will have to make periodic checks to ensure that the equipment specified is in fact being used, while the workers or the foreman on the job will have to make certain that installed equipment is not damaged by other trades while performing their respective work.

While other factors beyond your control may adversely affect the final electrical installation, job planning and carrying out this plan are largely the basis on which the work will be performed. Be certain that the planning is done on a sound basis.

Lists of crucial parts of the requirements appear in the discussions. These special sections cover:

• Grounding
• Switches
• Overcurrent protection
• Electric motors

• here's a link for better understanding of the Wiring calculations for commercial establishments: Commercial Electrical Wiring