620.62 Selective Coordination (Elevators)
What does 620.62 require when it comes to coordination?
When more than one driving machine is fed from a single feeder,
selective coordination is required between the overcurrent
protective device in each disconnecting means and any other
supply side overcurrent protective devices. Selective coordination
for elevator overcurrent protective devices is critical. For example,
in Figure 2, if a fault were to occur that would cause overcurrent
protective device M1 to open, all of the elevators in the building
would lose power. One of the reasons that coordination is so
important is because firefighters commonly use the elevator to get
closer to a fire during fire-fighting operations. See Figure 2.
ampacity, these two OCPDs cannot be coordinated together and
are not required to be. The only way to meet 620.62 with B4 and
F4 is to insure that both B4 and F4 are coordinated with M1. See
Figure 3.
Figure 3
Figure 2
Notice that each of the feeders supplies their own elevator. This
does not bypass the requirements of 620.62, which requires
selective coordination when there is more than one driving
machine being fed from a single feeder. According to Article 100,
a feeder is considered to be all circuit conductors between the
service equipment and the branch-circuit OCPD. This would mean
that the load side conductors from M1 would be a single feeder to
multiple driving machines. This would require F1, F2, F3, and F4 to
be selectively coordinated with M1 in order to comply with 620.62.
These situations would require selective coordination through to
the main OCPD in the building. Otherwise, safety may be
compromised if a fault occurs on the branch level that causes the
main OCPD to operate. For more information on selective
coordination see the discussion on 240.12 in this booklet or see the
Bussmann Electrical Protection Handbook SPD for a more in depth
discussion.
Since F2 (Feeder 2) is a single feeder to multiple elevators, the
branch OCPDs B1, B2, and B3 must be selectively coordinated
with F2 to comply with Section 620.62. Now look at the load side
of M1. This is also a single feeder to multiple elevators and must
also be selectively coordinated with F2, F4, and B4 in order to
eliminate the possibility of having a fault on one elevator cause the
upstream OCPD to open, thereby removing the power to the other
elevators. Since B4 and F4 are usually at or near the same
620.91 Emergency and Standby Power Systems (C)Disconnecting
Means (Elevators)
If there is a secondary source of power used for emergency purposes,
how is the elevator disconnecting means affected?
The disconnecting means referenced in 620.51 must be capable
of disconnecting all sources of power for maintenance purposes.
Hydraulic elevators have the capability of using a battery pack to
lower the elevator in a loss of power situation. The battery
attachment is utilized as an extra level of safety to keep from
stranding people in the elevator for long periods of time. Under
normal operation, the main line power from the disconnecting
means controls the raising of the elevator through a pump motor
and the lowering of the elevator through a solenoid and a drain
valve. To send the cab upward, the pump motor pumps hydraulic
fluid into the piston that forces the elevator upward. To return the
cab back down, a drain valve at the bottom of the piston is
opened by a solenoid valve and as the fluid drains back into the
reservoir, the elevator lowers. If the main line power is lost, this
battery pack attachment can supply enough power to actuate the
solenoid. See Figures 4 and 5.
Figure 4 – Normal Operation w/Out Auxiliary Contact
(DOES NOT COMPLY)
Elevator Disconnect
Without NC
Auxiliary Contact
l
+
Battery for
Lowering
Control Relay NC Contact
(While Relay is De-energized)
CR
Elevator Controller
Solenoid
Drain Valve
Elevator Motor
58
M
(To Lower Elevator)