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Elevator Electrical Requirements -NEC 620- National Electrical Code -page 2

620.51 Disconnecting Means (Elevators)

What are the requirements for the main elevator power disconnect?

620.51(A) requires a single disconnecting means that must be an enclosed externally operable fused motor circuit switch or circuit breaker that is capable of being locked in the open position and must be listed. 

What other concerns are there when installing this disconnecting means?

Since this is an elevator circuit, consideration needs to be made for the interaction with the elevator code (ANSI/ASME A17.1, Safety Code for Elevators and Escalators). While the electrical contractor does not usually get involved with the elevator installation, there are requirements from the elevator code that the electrical contractor needs to be aware of that may affect what he does have to install. The most influential of these requirements being Rule 102.2(c)(3) from ASME A17.1 which states that if sprinklers are installed in the elevator hoistway or machinery space then the elevator power must be removed prior to the application of water. NEC® 620.51(B) permits this removal of power on the disconnecting means to the elevator and can be accomplished with a fusible shunt trip switch. The reasons for removing this power is to reduce the hazards associated with water on live elevator electrical equipment. This includes, but is not limited to, the braking system of the elevator, which if water were applied may not be able to operate properly and may cause the elevator car to stop between floors and leave the hoistway exposed. Another concern is that the control circuitry for the door operation that is located on top of the elevator cab could become short-circuited when water is applied and allow the elevator to travel up and down with the doors open, again causing an exposed hoistway.

Since this removal of power is to occur prior to the sprinkler activation, there must also be interaction with the fire alarm system, which means involvement with NFPA® 72 (National Fire Alarm Code®). Shutdown is most commonly accomplished by the activation of a heat detector located in the hoistway or machine room. This heat detector is required to be located within two feet of each sprinkler head and is usually set at 135°F, compared to the fusible element of the sprinkler head, which is most commonly set at 165°F. (So, in theory, the system should operate as follows. First, the elevator is sent to a designated floor by the smoke detector, where the doors stay open. If the fire gets to the point where it is detected by the heat detector(s), power is removed before it gets hot enough to release water through the sprinkler heads.) When a fire alarm system is installed in a building, section 3-9.2.1 of NFPA® 72-1999 requires the elevator shutdown to be monitored for integrity. Since the fire alarm system usually operates at 24V and the shunt trip coil usually operates at 120V, they cannot be directly connected. This means that the heat detector should activate a relay (Isolation Relay), which in turn will allow power to be supplied to the shunt trip coil and cause the disconnecting means to open the circuit. This relay can be monitored for integrity by the fire alarm system to make sure that the wiring remains intact and must be located within three feet of the shunt trip device per 3-9.2.1. To help insure that the system is fail-safe, an additional relay (Volt Monitor Relay) is required by 3- 9.4.4 of NFPA 72-1999 to monitor for presence of the shunt trip voltage. This relay will be placed in parallel to the shunt trip coil so that it receives the same voltage. Then the contacts from this relay can be monitored for integrity by the fire alarm system. If at any time the voltage is not present to the relay, a trouble signal would be sent to the fire alarm system and annunciate an alarm so that someone will correct the problem. See Figure 1.

If contact closure occurs by either heat detector in Loop A, PLC 1 contact closes and energizes the Isolation Relay. When the Isolation Relay energizes, the IR Contact closes and the Shunt Trip Coil becomes energized, causing the switch to open and disconnect the power to the elevator. If the wiring in Loop A, Loop B, or Loop C becomes disconnected or short-circuited, the PLC will detect it and then close PLC 2 contact and cause the Trouble Signal Alarm to be activated which will notify someone that there is a problem that needs to be examined. This system is designed to be fail-safe so that if any problem occurs in the system, it can be fixed quickly and operational when it is needed to operate.

These requirements are commonly overlooked in the bidding process and usually cause extreme confusion. To find out more about how to comply with these codes and standards with one complete package, contact Bussmann® for information on the Power Module™ Switch and Panel for elevator circuits. The Power Module™ complies with these codes and standards and reduces contractor installation to a minimum in a UL listed assembly. For more information, including data sheets, look for Power Module™, under products, at www.bussmann.com.

Where should the disconnecting means be located?

620.51(C) requires the disconnecting means to be located where it is readily accessible and within sight of the elevator controller.

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