Utilization categories
In electrical engineering utilization categories are defined by IEC standards[1] and indicate the type of electrical load and duty cycle of the loads to ease selection of contactors and relays.
Definition
The utilization categories category for low-voltage switchgear defines the characteristic operating conditions for switchgear such as contactors, circuit-breakers, circuit-breaker-fuse units, contactor relays, etc. These devices are dimensioned for different electrical loads and for different operating conditions.
The characteristic of the load to be switched or controlled determines the requirements for the switchgear and its correct selection for the intended application. In particular, the stress on the switching path caused by current and voltage during switching on and off is of enormous importance. For example, the switch-on and switch-off current at resistance load corresponds to the continuous operating current, while, for example, squirrel cage motors consumes multiple of the rated operating current during switch-on and in the acceleration phase.
Utilization categories in IEC standard
Contact load in amperes for heaters (AC1) and motors (AC3) can be found directly on the contactor. The "Utilization category" are mainly categorized in IEC 60947 in the following volume:
- Volume 1: General requirements
- Volume 2: Circuit-breakers
- Volume 3: Circuit-breakers, circuit-breakers, switch-disconnectors and switch-fuse units
- Volume 4-1: Contactors and motor starters; electromechanical contactors and motor starters[1]
- Volume 4-2: Contactors and motor starters - Semiconductor motor controllers and starters for a.c. voltage
- Volume 5-1: Control apparatus and switching elements - Electromechanical control apparatus[1]
- Volume 6-1: Multi-function switchgear and controlgear - Mains switches (categories AC-32A/B)
- Volume 6-2: Multi-function switchgear and controlgear - Control and protective switchgear (CPS)
- Volume 7-1: Auxiliary equipment; Terminal blocks for copper conductors
- Volume 7-2: Ancillary equipment; protective conductor terminal blocks for copper conductors
In addition, IEC/EN 61095 also defines categories for "household and similar applications".
Table
The following table provides an overview of the various abbreviations. Within a utilization category, the suitable size may be selected for the respective type. This depends on the rated current, the rated voltage and the electrical load to be switched.
| Utilization category | Typical application[2][3] | Applicable IEC norm[3] |
|---|---|---|
| AC-1 | Non-inductive or slightly inductive loads, example: resistive furnaces, heaters | 60947-4-1 |
| AC-2 | Slip-ring motors: switching off | 60947-4-1 |
| AC-3 | Squirrel-cage motors: starting, switches off motors during running time | 60947-4-1 |
| AC-4 | Squirrel-cage motors: starting, plugging, inching | 60947-4-1 |
| AC-5a | Switching of discharge lamps | 60947-4-1 |
| AC-5b | Switching of incandescent lamps | 60947-4-1 |
| AC-6a | Switching of transformers | 60947-4-1 |
| AC-6b | Switching of capacitor banks | 60947-4-1 |
| AC-7a | Slightly inductive loads in household appliances: examples: mixers, blenders | 60947-4-1 61095 |
| AC-7b | Motor-loads for household appliances: examples: fans, central vacuum | 60947-4-1 61095 |
| AC-8a | Hermetic refrigerant compressor motor control with manual resetting overloads | 60947-4-1 |
| AC-8b | Hermetic refrigerant compressor motor control with automatic resetting overloads | 60947-4-1 |
| AC-12 | Control of resistive loads and solid state loads with opto-coupler isolation | 60947-5-2 |
| AC-13 | Control of solid state loads with transformer isolation | 60947-5-1 |
| AC-14 | Control of small electromagnetic loads | 60947-5-1 |
| AC-15 | Control of A.C. electromagnetic loads | 60947-5-1 |
| AC-20 | Connecting and disconnecting under no-load conditions | 60947-3 |
| AC-21 | Switching of resistive loads, including moderate overloads | 60947-3 |
| AC-22 | Switching of mixed resistive and inductive loads, including moderate overloads | 60947-3 |
| AC-23 | Switching of motor loads or other highly inductive loads | 60947-3 |
| AC-31A AC-31B ³) |
Non-inductive or weakly inductive loads | 60947-6-1 |
| AC-33A AC33B³) |
Motor loads or mixed loads including motors, resistors and up to 30% incandescent lamp load | 60947-6-1 |
| AC-35A AC-35B ³) |
Gas discharge lamp load | 60947-6-1 |
| AC-36A AC36B ³) |
Incandescent lamp load | 60947-6-1 |
| AC-40 | Distribution circuits of mixed resistive and inductive loads | 60947-6-2 |
| AC-41 | Non-inductive or weakly inductive loads, resistance furnaces | 60947-6-2 |
| AC-42 | Slip ring motors: Starting, switching off | 60947-6-2 |
| AC-43 | Squirrel cage motors: Starting, switching off during operation | 60947-6-2 |
| AC-44 | Squirrel cage motors: Starting, counter-current braking ¹) or reversing ¹), typing ²) | 60947-6-2 |
| AC-45a | Switching of gas discharge lamps | 60947-6-2 |
| AC-45b | Switching incandescent lamps | 60947-6-2 |
| AC-51 | Induction-free or slightly inductive loads, resistance furnaces | 60947-4-3 |
| AC-52a | Control of the stator winding of a slip-ring motor: 8-hour operation with starting currents for starting processes, maneuvering, operation | 60947-4-2 |
| AC-52b | Control of the stator winding of a slip ring motor: Intermittent operation | 60947-4-2 |
| AC-53a | Control of a squirrel cage motor: 8-hour operation with starting currents for starting processes, maneuvering, operation | 60947-4-2 |
| AC-53b | Control of a squirrel cage motor: Intermittent operation | 60947-4-2 |
| AC-55a | Switching of electrical controls of discharge lamps | 60947-4-3 |
| AC-55b | Switching incandescent lamps | 60947-4-3 |
| AC-56a | Switching transformers | 60947-4-3 |
| AC-56b | Switching of capacitor batteries | 60947-4-3 |
| AC-58a | Control of a hermetically sealed refrigeration compressor motor with automatic reset of overload releases: 8-hour operation with starting currents for starting, maneuvering, operation | 60947-4-2 |
| AC-58b | The control of a hermetically sealed refrigeration compressor motor with automatic reset of the overload trips: Intermittent operation | 60947-4-2 |
| AC-140 | Control of small electromagnetic loads with holding current ≤ 0.2 A; e.g. contactor relays | 60947-5-2 |
| A | Protection of circuits, with no rated short-time withstand current | 60947-3 |
| B | Protection of circuits, with a rated short-time withstand current | 60947-3 |
| DC-1 | Non Inductive or slightly inductive loads, resistance furnaces, heaters | 60947-4-1 |
| DC-3 | Shunt-motors, starting, plugging(1), inching(2), dynamic braking of motors | 60947-4-1 |
| DC-5 | Series-motors, starting, plugging(1), inching(2), dynamic braking of motors | 60947-4-1 |
| DC-6 | Switching of incandescent lamps | 60947-4-1 |
| DC-12 | Control of resistive loads and solid state loads with opto-coupler isolation | 60947-5-1 60947-5-2 |
| DC-13 | Control of D.C. electromagnetics | 60947-5-1 60947-5-2 |
| DC-14 | Control of D.C. electromagnetic loads having economy resistors in the circuit | 60947-5-1 |
| DC-20 | Connecting and disconnecting under no-load conditions | 60947-5-1 |
| DC-21 | Switching of resistive loads, including moderate overloads | 60947-5-1 |
| DC-22 | Switching of mixed resistive and inductive loads, including moderate overloads (i.e. shunt motors) | 60947-5-1 |
| DC-23 | Switching of highly inductive loads (i.e. series motors) | 60947-5-1 |
See also
- NEMA contact ratings
References
- ↑ IEC 60947 Standards for low-voltage switchgear and controlgear
- ↑ "IEC Utilization Categories". http://www.eecontrols.com/documents/Pages21-30.pdf.
- ↑ 3.0 3.1 "Niederspannungs-Schaltgeräte" (in de). https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/lvsam-rm001_-de-p.pdf.
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