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CLASS F.

44. Storage or Primary Batteries:

a. When current for light and power is taken from primary or secondary batteries, the same general regulations. must be observed as applied to similar apparatus fed from dynamo generators developing the same difference of potential.

b. All secondary batteries must be mounted on approved insulators.

[Section b. Insulators for mounting secondary batteries to be approved must be non-combustible, such as glass, or thoroughly vitrified and glazed porcelain.]

c. Special attention is directed to the rules (page 121) for rooms where acid fumes exist.

d. The use of any metal liable to corrosion must be avoided in connections of secondary batteries.

In a "primary battery" an electric current is produced by chemical action. If, for instance, a copper plate and a zinc plate are placed in a jar containing dilute sulphuric acid, chemical action produces an electrical pressure between the two plates, and if they be connected by a wire or other conductor forming a circuit, a current will flow. Batteries for operating the telegraph, call-bells, burglar-alarms, etc., are primary batteries.

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One form of "secondary' or "storage battery" is made by placing lead plates and sulphuric acid in a suitable jar and then forcing a current through the lead plates and acid. When the current passes, the lead plates are chemically changed, so that if after a time the battery be disconnected from the circuit by which current is furnished, it will act like a primary battery and will produce an electric current when connected to a circuit of wires or other conductors.

Batteries may be connected so that they will give a high electrical pressure or a large current, or both, and the same precautions are then to be taken with the wiring that would be taken if the current were coming from a dynamo. With primary batteries the pressure is ordinarily very low and the current very small, so that as far as danger from fire is concerned, usually little care need be taken.

Secondary batteries are mounted on insulators because salts formed by the chemical action frequently creep over the surface of the jars, and there would be leakage of the current if the jar were not properly insulated.

Acid fumes are often produced by batteries, and care must be taken that such action will not destroy the insulation or injure apparatus.

If the metal used about secondary batteries were to corrode and waste away, the carrying capacity of the

conductors would be lessened and excessive heating might occur.

45. Miscellaneous:

a. The wiring in any building must test free from grounds; i.e., each main supply-line and every branch circuit shall have an insulation resistance of at least 25,000 ohms, and should have an insulation resistance between conductors and between all conductors and the ground (not including attachments, sockets, receptacles, etc.), of not less than the following: :

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All cut-outs and safety-devices in place in the above. Where lamp-sockets, receptacles, and electroliers, etc., are connected, one-half of the above will be required.

This testing can, of course, be done satisfactorily only by those familiar with electrical instruments. All insulation allows minute leakage; that is, the resistance of the insulation is never infinite. It is not safe to allow more than a certain small amount of leakage to

a given length of conductor. An installation requiring only 10 ampères of current will presumably be a small one and the circuit a short one. For this reason a higher insulation resistance is required for a wiring system where the maximum normal current used is 10 ampères, than for one where it takes 1000 or 2000 ampères to supply all lamps. This insulation test is very useful as an indication, but it has principally a negative value. A low resistance indicates a fault, but a high resistance does not necessarily show perfect construction. There might be an air-space of a thousandth of an inch between a wire and a pipe, and this would prevent an indication of low resistance, but a jarring of the building might afterward bring the wire and the pipe into contact and cause a disastrous short circuit.

b. Ground-wires for lightning-arresters of all classes, and ground-detectors, must not be attached to gas-pipes within the building.

c. Where telephone, telegraph, or other wires connected with outside circuits are bunched together within any building, or where inside wires are laid in conduit or duct with electric light or power wires, the covering of such wires must be fire-resisting, or else the wires must be enclosed in an air-tight tube or duct.

d. All conductors connecting with telephone, districtmessenger, burglar-alarm, watch-clock, electric-time, and other similar instruments, must be provided near the point of entrance to the building with some protective device

which will operate to shunt the instruments in case of a dangerous rise of potential, and will open the circuit and arrest an abnormal current flow. Any conductor normally forming an innocuous circuit may become a source of firehazard if crossed with another conductor, through which it may become charged with a relatively high pressure.

WIRE-PROTECTORS.

[Protectors must have a non-combustible, insulating base, and the cover be provided with a lock similar to the lock now placed on telephone apparatus or some equally secure fastening, and be installed under the following require

ments:

1. The protector to be located at the point where the wires enter the building, either immediately inside or outside of the same. If outside, the protector to be enclosed in a metallic waterproof case.

2. If the protector is placed inside of building, the wires. of the circuit from the support outside to the binding-posts of the protector to be of such insulation as is approved for service wires of electric light and power, and the holes through the outer wall to be protected by bushing, the same as required for electric light and power service wires.

3. The wire from the point of entrance to the protector to be run in accordance with rules for high-potential wires; i.e., free of contact with building, and supported on noncombustible insulators.

4. The ground-wire shall be insulated, not smaller than No. 16 B. & S. gauge. This ground-wire shall be kept at

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