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    1. The input may be through a coupler or a gland.
    2. The outside surfaces shall be essentially of fireproof construction.
    3. A maintained contact, push-to-operate, emergency-stop switch (to remove incoming power) shall be located in a conspicuous place on the enclosure. If the input cable is protected by a ground-wire monitor, the enclosure shall include a ground-wire monitor test switch. One switch may satisfy both requirements.
    4. The primary circuit shall include short-circuit and overload protection.
    5. A power transformer shall isolate the battery being charged from the incoming power source. Power transformers with concentrically wound primary and secondary windings shall include a Faraday shield.
    6. The secondary circuit shall include short-circuit and overload protection.
    7. The power transformer secondary and all battery charging circuits shall be electrically isolated from the frame ground of the charger.
    8. Each charger output shall be through a multi-conductor cable that includes separate grounding and interlock conductors.
    9. The electrical contacts of battery charging connectors shall be arranged to open the interlock circuit before the charging circuit.
    10. The interlock circuit shall remove power from the charger output using either a contactor or a circuit breaker with contacts opening all ungrounded conductors in either the primary or secondary circuit. The interlock circuit shall have a manual reset feature.
    11. A voltmeter, ammeter, or other device that indicates the battery state of charge shall be part of each charging circuit.
    12. The charger shall include an end-of-charge circuit. The circuit shall either stop the charging current or reduce it to a level that can be continued without causing excessive gassing or temperature. This level is normally 3 to 6 amperes per 100 ampere-hours of the battery's six-hour rating. A timer is an acceptable means of providing this protection.