Type 1 and Type 2 Coordination on Motor Feeders
Type 2 coordination: The coordination type defines what damage is acceptable in a motor feeder after a short circuit. With Type 1 the contactor and thermal relay may be damaged; with Type 2 no damage beyond light contact welding is expected and the circuit can be returned to service quickly.
Contents
A motor feeder is not a single device but a combination of short-circuit protection, a switching element and overload protection. These three behave together during a short circuit, and the limit of the resulting damage is set by the selected coordination type. Assembling the combination from arbitrarily chosen devices means the figures printed in the catalogue have no equivalent in the field.
What coordination defines
IEC 60947-4-1 describes the condition of a motor feeder combination after a short circuit with two levels of acceptance. In both types the basic requirement is the same: the operator must not be endangered and no damage may occur outside the combination. The difference lies in how much damage inside the combination is acceptable. The coordination type is therefore not a technical detail but a decision about how quickly the plant wants to return to production after a fault.
The difference between Type 1 and Type 2
With Type 1 coordination, damage to the contactor and the thermal relay after a short circuit is accepted; devices may need replacement and no restart is expected before repair. With Type 2 coordination, no damage other than easily separable light welding of the contacts is allowed, the thermal relay must retain its setting and the combination must be able to return to service without repair. In plants where a process stop is expensive, Type 2 is the natural choice.
Combination architectures
The classic arrangement builds short-circuit protection with aM fuses while a contactor performs switching and a thermal relay provides overload protection. The second common arrangement combines a motor protection circuit breaker with a contactor, gathering short-circuit and overload functions into one device and saving space in the panel. A third option uses a moulded case breaker with an adjustable electronic trip unit together with a contactor and an electronic motor protection relay, which suits larger ratings and installations with high monitoring requirements.
Manufacturer combination tables and verification
| Property | Type 1 coordination | Type 2 coordination |
|---|---|---|
| Damage after a short circuit | Contactor and thermal relay may be damaged | No damage beyond light contact welding |
| Return to service | Device replacement may be required | Service continues after separating contacts |
| Thermal relay setting | May need to be reset | Setting is retained |
| Typical use | Non-critical auxiliary drives | Process motors where continuity is critical |
| Cost and space | Lower | Higher, with a restricted device choice |
Coordination type is not proven by calculation but by type tests performed by the manufacturer. Each manufacturer therefore publishes combination tables showing which set of devices achieves which coordination type at a given prospective short-circuit current and voltage. A pairing outside the table is not valid even when the devices carry identical ratings. The table below compares the two coordination types and summarises the operational consequences of the choice.
Application in an MCC and maintenance
In a motor control centre every drawer is a combination, so the drawer label must show motor rating, protection settings and the coordination type. At commissioning, the thermal relay is set to the motor rated current and the setting is recorded. After a short circuit on an outgoing way, contacts are inspected visually even in a Type 2 combination, settings are verified and the event is added to the maintenance file. Spare part stock is planned according to the combination table in use.
Key takeaways: Type 2 coordination
- Decision criterion — Coordination type follows the target time to return to production after a fault.
- Proof by testing — Coordination is verified by manufacturer type tests and combination tables, not by calculation.
- Architecture choice — Fuse based sets, motor protection circuit breakers or breaker based sets fit different needs.
- Field discipline — Drawer labels must show protection settings and the coordination type.
- Standard source — IEC publication catalogue: iec.ch.
Frequently asked questions
Can devices of different brands with the same rating be combined?
They can be assembled, but the coordination type cannot be guaranteed. Coordination depends on how the devices behave together during a short circuit and is declared only for combinations tested by the manufacturer.
Is Type 2 coordination required on every motor?
Not necessarily. Type 2 is preferred on process motors where downtime is expensive, while Type 1 can be an economical solution on redundant or non-critical auxiliary drives.
Is a thermal relay still needed with a motor protection circuit breaker?
A motor protection circuit breaker covers both short-circuit and overload functions, so a separate thermal relay is unnecessary. A PTC evaluation relay is still added where thermistor based temperature protection is specified.
Related articles
- Motor Protection: Thermal Relay, MPCB and PTC Compared
- Contactor Selection: AC-1 and AC-3 Utilisation Categories and Electrical Life
- What is a Motor Control Center (MCC)? Structure and Applications
- All technical articles
Let us select your motor feeder combinations against short-circuit figures and continuity targets using coordination tables; Devpan builds motor control centres with tested combinations. Related Devpan solution: DevControl MCC panel.
