lamp. You will read infinity. Remember, "infinity" means that the circuit is good, and "continuity" means a short. Now, connect the ohmmeter between the neutral and the lead going to the middle lamp. The reading will show continuity, indicating the short is beyond Point A. You should leave Point A open at this time and continue on to the middle lamp.
Disconnect Point B and take the same readings that you took at the first light. From these tests you can determine that the circuit between the first and middle lamp is all right (infinity reading), and the trouble must be between the second and third lamp. By checking closely at the middle junction box, you can probably see charred or frayed wires indicating the problem. You may need to continue your check to Point C. Use the same procedure as with the other lamp, and find the trouble between Points A and C.
After installing the switches needed to control the lighting, you need to mount the light fixture itself. Each lighting installation is designed to produce a specific level of illumination adequate for those working in the area. The amount of illumination initially provided starts to decline almost as soon as it is put in operation. This reduction is caused by dirt on the lamps and luminaries, a decrease in lamp lumen output, and dirt on the room walls and ceilings. Illumination should be sufficient to eliminate eyestrain, support a high level of production, and promote safety and employee morale.
Lighting fixtures are designed for a particular lamp size and type. Many fixtures, however, were installed in military buildings long before the manufacturers started producing higher and higher wattage lamps in ever smaller envelopes. Consequently, it is possible to use much higher wattage lamps than the fixture or the circuit can handle adequately.
CAUTION Excessive heat of higher wattage lamps can damage the sockets, increase failure rate, and overload the circuits. Personnel are cautioned to use only the lamp size (in watts) recommended for the fixture, rather than a higher wattage lamp that may physically fit.
Incandescent lamps come in a variety of voltage ratings. For most applications, the lamp voltage rating nearest the available line voltage should be selected. Under this condition, the lamp will produce its rated values of life, watts, and light output. Many incandescent lamps are available with life ratings considerably in excess of ordinary general service lamps. Some have ratings of 5,000 hours or more, and some even are guaranteed to burn for 5 years. General use of these lamps is not recommended because the initial cost is comparatively high and the extended life is gained by reducing the light output. There are, however, a few areas where it is necessary to use bulbs with a long life. Typical locations include high-ceiling auditoriums, exit lights, stairwells, and marker lights on towers or fire alarm boxes. For these areas, do not use a special rated lamp. Do use an ordinary general service lamp whose voltage rating is higher than the circuit voltage; for example, 130-volt or higher lamps for 120- volt circuits. When you are operating the lamp below its rated voltage, the life is increased at a sacrifice in light output. For general use, the lamp voltage rating nearest the available line voltage should be used.
Many kinds of incandescent lamps are especially designed for placement in a variety of situations; for example, under severe physical conditions (such as vibration or extreme temperatures), in inaccessible locations, or when special lighting effects are desired. Some of these types of incandescent lamps and their uses are as follows:
INSIDE-FROSTED LAMPS are used in most fixtures designed for incandescent lamps. The frosted finish reduces lamp brightness and glare.
CLEAR LAMPS are used in fixtures where control of the light is required (such as in reflectors having polished reflecting surfaces and in enclosed globes or reflectors of prismatic glass), particularly where concentrated light control is required, as in high, narrow bays.
Reflector equipment of the diffusing globe type, where the lamp protrudes through the bottom of the fixture, requires WHITE BOWL LAMPS. The white bowl reduces the surface brightness and glare from the working surfaces.
SILVERED-BOWL LAMPS are used principally for indirect lighting and in reflector equipment. The fixture parts should not touch the lamp as the thermal expansion may cause the bulb to crack and fail prematurely.
REFLECTOR LAMPS with the reflecting surface inside the lamp are, in effect, a fixture in themselves. A collection of dust and dirt on the exterior of the lamps can cause them to lose their effectiveness.Continue Reading