Coordination of a motor starter describes how the short-circuit protection, the contactor and the overload relay behave together when a fault occurs. In type 1, the contactor and relay may be damaged, as long as there is no danger to people or the installation. In type 2, the relay may not suffer damage and the contactor allows at most light contact welding that is easy to separate. It is verified by testing the complete combination, and only the manufacturer can declare it.
Why coordination exists
In a motor starter, three functions with very different response speeds live together. The contactor switches the motor in normal service. The overload relay protects against slow heating. And the short-circuit protective device, a fuse or a breaker, must clear a fault in milliseconds. When a short circuit occurs, the contactor and the overload relay are in the fault current path, and the question is what happens to them before the protection opens.
Coordination answers that question with a standardized classification. It is the term in IEC 60947-4-1 for describing the combination of contactor, overload relay and short-circuit protection, and the level of damage accepted after a fault.
Type 1 and type 2
| Aspect | Type 1 | Type 2 |
|---|---|---|
| Damage allowed to contactor and relay | Damage is accepted; parts may need repair or replacement | The relay suffers no damage; the contactor may have light contact welding, easy to separate |
| Safety | The device must not endanger people or the installation | The same condition, plus continued service after the fault |
| Return to service | After repairing or replacing components | After inspection, without replacing parts of the assembly |
| Switchgear cost | Lower | Higher, due to larger sizes or current-limiting devices |
| Cost of the outage | Higher, due to replacement | Lower |
The key is the type of damage that is accepted, not a promise of “zero damage”. In type 1 the contactor and overload relay can be left unusable: melted or welded contacts, burned heating elements. In type 2 no damage is accepted in the relay or in any component other than the lightly welded contact. This does not depend on a single device: it depends on the combination.
How it is verified
Coordination is declared after short-circuit tests on the complete combination. The tests apply fault currents of different magnitudes, from high overloads to bolted short circuits, because behavior changes. At moderate currents, the risk is that the relay and contactor suffer during the time the protection takes. At high currents, the risk is the energy the limiting device lets through. That is why manufacturers’ tables are by short-circuit current interval and by voltage.
Three practical consequences:
- The table rules. A combination is valid only with the exact models and ratings in the table. Replacing the fuse with another “equivalent” or the relay with one of another brand means coordination is no longer declared.
- The panel short-circuit current decides. A combination may reach type 2 up to a certain current and type 1 above it. You must know the expected current at the starter location.
- Voltage matters. Tables are published by supply voltage; the one that works at 400 V may not hold at 690 V.
The tests also require the overload relay to keep its curve and calibration, which is a different point from “not burning out”: a relay that survives but loses calibration does not comply.
How to decide which to specify
- Does an outage after a short circuit affect a continuous process or a critical function?
- Yes: Specify type 2 with the manufacturer's table
- No: Are spares available and staff able to replace them quickly?
- Yes: Type 1 is enough
- No: Specify type 2 or keep spares on site
This decision is about cost and risk, not minimum compliance. It goes in the specification as a requirement, because otherwise each contractor chooses the cheapest type. On motors that feed plant safety systems, fire pumps or essential services, type 2 is usually the criterion.
Illustrative example
Invented figures.
A plant has several 7.5 kW pumps at 400 V. A short circuit in the cable of one of them would melt the contactor contacts and burn the thermal relay heating elements under type 1 coordination. The cost of replacing the contactor and relay is low (illustrative: equivalent to an hour of work and low-value spares), but the pump outage lasts half a day while the parts arrive. If the pump is one of several in parallel, the loss is zero and type 1 is reasonable. If the pump is the only one feeding the cooling of a process, that half day of outage costs more than the extra cost of type 2 switchgear for the whole room, and the decision changes. The number of pumps does not define the type; the consequence of one being out of service does.
Coordination, selectivity and conductor protection
Three concepts are often mixed up and are worth separating.
Coordination. It deals with damage to the starter when a short circuit occurs in the motor circuit. It is a property of the combination of devices in the starter itself.
Selectivity (discrimination). It deals with which device in the network opens on a fault: the one closest to it, so the rest of the installation stays energized. It is a property between protection levels, for example between a branch breaker and the main feeder breaker. A starter with type 2 coordination can still be poorly selective with the upstream breaker. With that miscoordination, a fault on one motor can trip the whole panel.
Conductor protection. The cable feeding the starter and the one going to the motor must withstand the fault current for the time the protection takes to open. The energy the protective device lets through must be lower than what the cable withstands. That check is made with the limiting characteristics of the fuse or breaker and not with the cable size alone.
All three problems are solved with the same data: short-circuit current at each point, characteristics of each device and the manufacturer’s coordination tables. That set is what is normally documented in a short-circuit and coordination study. A plant that has grown over time usually has panels with different coordination types, from different periods and manufacturers, and a study shows which are within the table and which have drifted away from it.
One final point: the declared coordination type covers the first fault. After a short circuit, even if the starter is type 2, inspect the contacts and relay and check the condition of the cable and motor before restoring power. A motor fault that has already happened once is likely to happen again.
A practical consequence for maintenance: the coordination table and the list of authorized spares must be within reach of whoever replaces a fuse or a relay. The panel is often correct on commissioning day and stops being so two years later, when an emergency replacement substitutes one part for a “similar” one. A label with the exact part number and a procedure that requires consulting the table before replacing any component prevent this drift, which is the most common way of losing coordination.
Common mistakes
- Asking for “type 2 coordination” without asking for the manufacturer’s table that proves it.
- Replacing the fuse or the relay with one of another brand during maintenance.
- Applying a 400 V table to a 690 V circuit.
- Using a combination whose coordination holds up to a certain current in a panel with a higher short-circuit current.
- Assuming that a motor with a soft starter or drive follows the same coordination as the direct contactor.
- Confusing coordination with selectivity: the first deals with damage to the starter, the second with which device opens first in the network.
- Not leaving the table or the brand of the authorized components in the panel.
Checklist
- Coordination type required by the specification and its justification.
- Expected short-circuit current at each starter location.
- Manufacturer’s coordination table for the exact combination and supply voltage.
- Short-circuit protective devices, contactors and relays with the table’s part numbers.
- Spares and replacement procedure for type 1.
- Contact inspection and relay calibration check after any short circuit.
- Label in the panel with the authorized components.
- Coordination reviewed whenever the source or transformer changes.
When to call us
Coordination is lost silently: a spare change, a new transformer or an expansion can take it outside the table without anyone noticing. Our team can carry out your short-circuit and coordination study remotely, worldwide, and test and commission the panel protections in Colombia, or elsewhere on request. Write to us through contact with the single-line diagram and the list of starters.
Related guides
- Thermal overload relay and trip classes 10A, 10, 20, 30
- Motor circuit protection: fuses and conductor
- Motor circuit breaker (MPCB): how to select one
- NEMA vs IEC motor starters and contactors
- Induction motor protection: 49, 46, 50/51, 37, 66, 87M
- Intelligent MCC: CENTERLINE 2100, SIVACON S8, MNS, Okken
- LV Motor Protection: TeSys T, SIMOCODE pro and E300
- Medium-Voltage Vacuum Contactor: Fuses, Motors, Tests
- Soft Starters: ABB PSTX, ATS480, Siemens 3RW, WEG SSW900
- Motor 49 Overload Trip: Causes and Diagnosis
References
- IEC 60947-4-1, Low-voltage switchgear and controlgear – Part 4-1: Contactors and motor-starters – Electromechanical contactors and motor-starters.
- Motor switchgear manufacturers’ technical guides on type 1 and type 2 coordination.
Frequently asked questions
Does type 2 coordination mean the starter is not damaged?
Not exactly. After the short circuit there is no damage to the overload relay or other components, and the contactor contacts may be left with a light weld that separates easily. The starter may need a contact inspection, but it must be able to work again without replacing parts.
How do I know if my combination meets type 2?
Only the manufacturer's coordination tables declare it, for a precise combination of short-circuit protection, contactor and relay, at a given voltage and short-circuit current. Replacing one component with another of the same "family" or from another manufacturer invalidates the table.
When is it worth requiring type 2?
When a long outage after a short circuit costs more than the difference in switchgear: continuous processes, critical motors, remote installations or where parts take a long time to arrive. For non-critical duties with spares available, type 1 is usually enough.
Does a motor circuit breaker already guarantee coordination?
An MPCB protects the circuit, but coordination remains a property of the combination with the contactor downstream. Check the manufacturer's table for the type reached at the available short-circuit current.