620.61 Overcurrent Protection (Elevators)

What requirements must be met for overload protection?

Most elevators are rated for intermittent duty and 620.61(B)(1) requires the elevator motor to be protected against overloads by 430.33. This section says that if a motor is rated as intermittent or similar duty, it is allowed to be protected against overloads by the branch-circuit short-circuit overcurrent protective device provided it does not exceed the values specified in Table 430.52. If the motor is rated for continuous duty, such as for escalators and moving walks, 620.61(B)(2) requires the overload protection to be sized in accordance with 430.32. This means that it must have a separate overload device sized no greater than 125% of FLA.

What about short-circuit protection?

According to 620.61(D), short-circuit protection is to be provided by the branch-circuit overcurrent protective device and must be sized in accordance with Article 430 Part IV.

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. 

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 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. 

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.

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