Figure 7-3. - Branch-circuit layout #3.
equipment, you may not exceed them even if higher values are indicated in table 430-152 of the NEC® ; however, you may use branch-circuit protective devices of smaller sizes. If you use a branch-circuit device that is smaller, you only need to be sure that it has sufficient time delay to permit the motor-starting current to flow without opening the circuit.
Often it is not convenient or practicable to locate the branch-circuit short-circuit and ground-fault protective device directly at the point where the branch-circuit wires are connected to the mains. In such cases, the size of the branch-circuit wires between the feeder and the protective device must be the same as the mains unless the length of these wires is 25 feet (7.6 meters) or less. When the length of the branch- circuit wires is not greater than 25 feet, the NEC® rules allow the size of these wires to be such that they have an ampacity not less than one third of the ampacity of the mains if they are protected against physical damage.
Figure 7-4 gives you an example of branch-circuit conductor sizing, using the figures found in the NEC® tables 430-152 and 430-7(b).
You may use a single-branch circuit to supply two or more motors or one or more motors and other loads according to section 430-53 of the Code. Some examples are as follows:
1. Several motors, each not exceeding 1 horsepower, are permitted on a branch circuit protected at not more than 20 amperes at 120 volts or less, or at 600 volts or less protected at not over 15 amperes if all of the following conditions can be met:
The rating of the branch-circuit short-circuit and ground-fault protective device marked on the controllers is not exceeded.
The full-load rating of each motor does not exceed 6 amperes.
Individual overload protection conforms with section 430-32 of the NEC® .
2. You may connect two or more motors of any rating to a branch circuit that is protected by a short- circuit and ground-fault protective device selected according to the maximum rating or setting of the smallest motor.
3. You may connect two or more motors of any rating and other loads to one branch circuit if the overload devices and controllers are approved for group installation and if the branch-circuit fuses or circuit- breaker rating is according to section 430-52 of the NEC® .
Overcurrent protection for a feeder to several motors must have a rating or setting not greater than the largest rating or setting of the branch-circuit protective device for any motor of the group plus the sum of the full-load currents of the other motors supplied by the feeder.
Protection for a feeder to both motor loads and a lighting and/or appliance load must be rated on theContinue Reading