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ELECTRICAL UNITS.

AMPERE. — The unit of current strength. It is the flow of electricity produced by the pressure of one volt on a resistance of one ohm.

COULOMB. — The unit of electric quantity. It is the amount of electricity which flows past a given point in one second on a circuit conveying one ampere.

FARAD. — The unity of capacity. A condenser that will hold one coulomb at a pressure of one volt has a capacity of one farad.

OHM. — The unit of electrical resistance. Ohms law states that the current in any circuit is equal to the E. M. F. acting on it divided by its resistance.

VOLT. — The unit of electro-motive force or pressure analogous to the head of water in hydraulics.

WATT. — The unit of work.

power, i.e. 746 Watts equal 1 horse power. We may find the Watts used in a circuit by three formulae, thus:

Watts = Amperes (squared) x ohms.
Watts = Amperes x volts.
Watts = Volts (squared) - by ohms.

MILLI-AMPERE. —Onc-mUuontfa ampere and is used as the unit of current when the amount is very small. Its use avoids fractions.

KILO-WATT is the unit for dynamo and even transforms capacity. It means 1000 watts and hence large capacities can thus be expressed by use of but few figures.

RULES AND REGULATIONS

Of the New England Insurance Exchange and Boston Fire Underwriters' Union for electric lighting. [Adopted April 15th, i88g, and superceding all previous rules.]

ARC SYSTEM.

OUTSIDE WIRES.

1. All outside overhead wires must be covered with some material of high insulating power, not easily abraded; they must be firmly secured to properly insulated and substantially built supports. All tie wires must have an insulation equal to that of the conducting wires.

2. All joints must be so made that a perfectly secure and unvarying connection, fully equal to the cross-section of the conducting wire will be secured — and they should be soldered. Resin should not used as a flux. Nothing but an acid solution should be used, and any excess should be washed off before the splice is covered. This also applies to inside wires All joints must be securely wrapped with an approved tape.

The following formula for soldering fluid is recommended, viz: —

Saturated solution of zinc 5 parts

Alcohol 5 parts

Glycerine 1 part

3. Care must be taken that conducting wires are not placed in such a position that it would be easy for water, or any liquid, to form cross connection between them, and they should not approach each other nearer than one foot.

4. The wires must never be allowed in contact with any substance other than air, and their proper insulating supports.

5. Conducting wires carried over or attached to buildings, must be at least seven feet above the highest point of flat roofs, and one foot above the ridge of pitch roofs. Lines constructed subsequent to the adoption of these regulations should not be run over and attached to buildings other than those in which the light or power is being, or is to be used, but should be on separate poles, or structures, where they can be easily reached for inspection.

6. When they are in proximity to other conducting wires, or any substance likely to divert any portion of the current, dead, insulated guard-irons must be placed so as to prevent any possibility of contact in case of accident to the wires, or their supports. The same precautions must be taken where sharp angles occur in the line wires, and also where any wires (telegraph, telephone, or others) could possibly, owing to their position, come in contact with the electric light wires.

7. Overhead wires from the main circuit or pole in the street to the terminal insulators attached to buildings, and at the point where they enter a building, must not be less than twelve inches apart. They must be rigidly and neatly run, and supported by glass or porcelain insulators, or rubber hooks. The rubber hooks must be of an approved pattern, i. e., with the rubber insulation free from flaws, and projecting over the hook in cup form.

8. Service blocks must be protected by at least two coats of water-proof paint over their entire surface; and when used to support rubber hooks, must have at least one inch of wood between the inner end of the hook and the back of the block.

9. For entering buildings, wires with an extra heavy water-proof insulation must be ustd from the terminal insulators outside to the inside of a building They must loop down, so that water may drop off, without entering the building, and the holes through which they enter should, where possible, slant upward. If an approved glass insulator for bushing the hole is used, the extra heavy water-proof insulation will not be required.

10. Service wires must come in contact with nothing save air, and their insulating supports, except in unavoidable cases, when a wire with an extra heavy insulation suitable for the purpose must be used.

11. The use of porcelain knobs as insulators, except in perfectly dry places, or for the support of specially insulated wire, will not be accepted, unless of some approved shape.

12. None but an approved tubing will be accepted as a durable water-proof insulation.

13. Wires must enter and leave the building through an approved cut-out switch.

14. The cut-out switch must be "double contact," and should effectually close the main circuit, and cut off the interior, when turned "off." It must be so constructed that there shall be no arc between the points when thrown "on " or "off." It should be automatic in its action in either direction, not stopping between points when once started. It should indicate upon inspection whether current be "on" or "off."

15. It must be mounted on a non-conducting base, kept free from moisture, and easy of access to firemen and police.

INSIDE WIRING.

16. Wires must not be concealed; they must be run in plain sight so as to be open to inspection at any time. They should be kept apart at least twelve inches.

17. In perfectly dry places wires may be supported by cleats of wood (filled to prevent the absorption of moisture) or porcelain. Cleats should be so made as to separate the wire at least one-fourth of an inch from the building.

18. In places liable to dampness, wires must be separated at least one and one-half inches, they must be thoroughly and carefully put up, and supported upon por

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