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What is the definition of the NEMA wiring classes (Class 1 or 2, Type A, B, or C)?

Issue:
Definition of NEMA wiring classes.

Product Line:
N/A

Environment:
Motor Control Centers

Cause:
Code Definition

Resolution:

NEMA/EEMAC Wiring Classes and Enclosure Types
Wiring Classes

Class 1—Independent Units
Class 1 motor control centers consist of mechanical groupings of combination motor control units, branch feeders, other units, and electrical devices arranged in a convenient assembly. The manufacturer completes wiring between components within each unit. Wiring between units is not required.
 
Class 2—Interconnected Units
Class 2 MCCs are the same as Class 1 MCCs with the addition of manufacturer-furnished electrical interlocking and wiring between units as specifically described in the overall control system diagrams supplied by the purchaser.​

Type A
User (field) wiring connects directly to device terminals internal to the unit. Type A wiring is provided only on Class 1 MCCs.

Type B
User (field) control wiring connects to unit terminal block(s) in or adjacent to each motor control unit. User load (power) wiring for Size 3 or smaller combination motor control units connects as follows:
Type B-D
User load (power) wiring connects directly to the device terminals, which are located immediately adjacent to, and are readily accessible from, the vertical wireway.
Type B-T
User load (power) wiring connects to factory-wired power terminal blocks located in or adjacent to each unit.
User load (power) wiring for Size 4 or larger combination motor control units and branch feeder units connects directly to the unit device terminals.

Type C
User (field) control wiring and load wiring on Size 3 or smaller motor control units connects to master terminal blocks mounted at the top or bottom of those vertical sections containing control units. Unit control wiring and load wiring on Size 3 or smaller units are factory-wired from unit-located terminal blocks to the master terminal blocks.
User load (power) wiring for Size 4 or larger units connects directly to the device terminals. As an option, user load (power) wiring for all sizes of motor control units may connect directly to the device terminals within the MCC units. See page 85 for load wiring options.


See this information in our Model 6 MCC Catalog.
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