When you're designing an electrical system for a building, don't let elevator requirements bring you down.
The many codes and guidelines that regulate the electrical design of an elevator can seem overwhelming, and dealing with the electrical inspector, elevator inspector, and Fire Marshal can be even more intimidating. As they review the plans and the construction site, they may have conflicting interpretations or requirements. And as the designer, you can become the fulcrum on which all of these requirements and authorities exert their leverage, but an understanding of elevator basics can help you handle the pressure.
The two main types of elevators are hydraulic and traction. Hydraulic elevators comprise a hydraulic reservoir, pump, cylinder, and controller. The pump sends hydraulic fluid from the reservoir to the cylinder, buried deep below the elevator shaft. Fluid pressure in the cylinder raises and lowers the elevator cab. Limit switches placed throughout the height of the shaft communicate with the controller and stop the cab at each landing. Cylinders in hydraulic elevators usually aren't suitable for buildings taller than five stories. In such cases, it's economically justifiable to specify a traction type elevator.
Traction elevators raise and lower the elevator cab with cables, a pulley system, and counter weights powered by a motor at the main drive wheel. Motors for traction elevators were traditionally DC or synchronous, but new installations use AC motors and VFDs for speed control.
The elevator equipment room that serves a hydraulic elevator is almost always located on the lowest floor adjacent to the elevator shaft. A traction elevator's equipment room is typically located at the top of the building, directly over or adjacent to the shaft.
Your elevator supplier will take care of all the wiring and related code requirements for the elevator cab and the various controls. You'll be responsible for specifying the items related to the fire alarm and some controls, as well as supplying lighting and power to the equipment room and elevator pit.
First, you'll need to install lighting in the elevator equipment room (Photo 1) and shaft pit (Photo 2). Luminaires must be lensed or equipped with wire guards to protect the lamps. The light switch for the equipment room must be adjacent to the entrance door on the latch side. The light switch in the pit must be mounted 42 in. above the seal plate, adjacent to the ladder. You need at least one 120VAC GFCI-protected receptacle at each location. The circuit(s) for the lighting and receptacles must be dedicated to the elevator area only.
Power for the elevator controller must first enter a lockable safety disconnect device, located adjacent to the door of the equipment room. This device must be either a fused disconnect or a circuit breaker because ANSI/ASME A17.1 requires you to install an additional overcurrent protection device (OCPD) in the elevator equipment room. A separate 120VAC, 15A circuit is required for cab lighting and accessories, and it must have its own local disconnect and OCPD in the equipment room as well. You must run a separate insulated grounding conductor with the feeder conductors from the electrical source to the elevator controller. The conduit alone can't act as the grounding means.
Elevator cab lights require emergency back-up power. If the building has emergency power available, use it to supply the cab lights. Otherwise, specify that the elevator supplier provide a battery back-up unit to power the lights in the event of an outage.
You'll need to run telephone cables to the equipment room control panel, but the elevator supplier will take care of getting the cables to the elevator cab. The Americans with Disabilities Act Accessibility Guidelines for Buildings and Facilities (ADAAG) now require the cab to have a special phone accessible by individuals with disabilities. In the event of a breakdown, that phone must automatically call a location staffed 24 hours a day.
Smoke detectors, which are required in all elevator lobbies and elevator equipment rooms, must be connected to the elevator controllers directly by means of auxiliary contacts and wiring, or indirectly by means of output signals from the fire alarm control panel. If a smoke detector goes into alarm, it signals the elevator to go into “Fire Recall Function,” at which point the controller directs the elevator cab to travel to its pre-programmed designated landing, open its doors, and remain stopped there until the alarm clears. The floor specified as the designated landing, which must be approved by the Fire Marshal, is usually the floor on grade level so passengers can quickly exit to the outside.
If the smoke detector at the designated landing goes into alarm, the elevator will stop at a predetermined alternate floor, which is usually the floor above the designated floor. However, this can vary depending on building conditions and exterior grade. Therefore, there will be two signals to the elevator control panel related to smoke detectors: one from the “designated floor” smoke detector and another combined signal from the smoke detectors at the other lobby landings and in the equipment room.
Regardless of the number of elevators, only one smoke detector is required at each floor lobby, but it must be located within 21 ft of every elevator door. Be sure to provide a horn/strobe alarm in large equipment rooms because they can be noisy, isolated places.
To safeguard the passengers and electrical equipment, ASME A126.96.36.199.3.2 requires the power source to the elevator control panel to shut down prior to the discharge of water from a sprinkler head. Depending on your local codes, you can do this by installing heat or smoke detectors within 24 in. of the sprinkler heads.
If a hydraulic elevator loses power because a heat detector goes off — or for any other reason — it could trap occupants for an unpleasant amount of time. To avoid this situation, designers can specify elevator controls with a safety feature commonly called a rescuvator. Upon loss of power, the rescuvator controls the cab, lowers it to the designated floor, and opens its doors. If you specify a rescuvator, you must also specify a disconnect switch with an auxiliary contact that opens when the disconnect arm moves to the open position, but stays closed when the OCPD trips. This switch will ensure that the elevator won't descend into the elevator pit and allow maintenance people to work safely in the area beneath the cab.
Where a feeder powers more than one elevator, you need selective coordination; the OCPDs must be series-designed so a fault at one of the elevators will be cleared by only the OCPD serving it. The feeder OCPD needs to remain closed so the remaining elevators have power and continue to function.
Modern electronic elevator controls can be sensitive to temperature shifts. Therefore, elevator equipment rooms must maintain a temperature between 50°F and 90°F. This will normally require you to vent the room with a fire/smoke damper and include smoke detector signals in the control logic.
If your specifications require a vent at the top of the shaft for venting smoke, you must provide a key switch with a pilot light to control that vent. You must locate this key switch at the main lobby or at the building fire command center.
The new ADAAG guidelines now require that emergency power be available to elevators that have four or more stories of travel above or below the accessible floor [4.1.3(9)(1)].
If you provide your elevators with emergency power, you must run communications wires between the automatic transfer switch (ATS) and the elevator control panel. This accomplishes two functions. First, the ATS signals the elevators that it's about to switch over to emergency power — preferably 30 sec or more prior to switching, which allows the elevator controller to bring each elevator cab to the nearest landing and stop, thus protecting the motors and electrical system. Next, with multiple elevator banks, the controller will usually allow only one elevator at a time to operate, reducing the amount of emergency power required.
High-rise buildings pose additional concerns. The Uniform Building Code requires two-way communications between the central command center and the elevators, each elevator lobby, emergency power rooms, and by entries into enclosed stairways (Section 403.5.3). Fireman telephone jacks and telephone cabling are typically sufficient for each of these locations. Firefighters can then use portable telephone handsets in combination with the jacks and cabling.
The various items to consider and check when designing for elevator installations have many potential pitfalls. But by understanding how these items fit together and what purpose they serve, you can have a successful project. Always verify all conditions and requirements with the state and the AHJ where the installation is taking place.
Granle is a licensed professional engineer with Sebesta Blomberg & Associates, Rochester, Minn.