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Page 289

| 15 Storage Batteries |

| Control Systems |

| The need for continuity in the supply of energy for the control of circuit breakers and other auxiliary equipment has led to reliance on storage batteries. Although relatively little energy is consumed by the control system, its reliability must be of the highest order since a failure may result not only in serious damage to equipment but to the entire circuit as well. The control system provides for the electrical operation of such relays, circuit breakers, pilot lights, alarms, recording meters, and other such instruments that are all connected to a dc control bus. This bus is supplied with energy from a storage battery. |

| Demand on the control system may be divided into two classes. The first is a small, practically constant load, comprising the position-indicating and pilot lights, relay and meter coils, and other similar devices requiring a constant supply of current. The second class of load, which constitutes the supply to solenoids and motors of electrically operated equipment, including circuit breakers, is of a momentary nature but of heavy demand. If the control battery is also required to supply emergency lighting to the area in which the electric equipment and controls are housed, a third class of load is added. This third class may be of comparatively greater magnitude and longer duration. |

| Control systems may be operated at nominal voltages of 6, 12, 24, 48, or 120 V, although 24-, 48-, and 120-V systems are preferred. They are usually designed for ungrounded operation, with some type of ground detection provided. |

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