Overload Relay Coordination: Type 1 vs Type 2 with Contactor and SCPD
What is Type 1 vs Type 2 coordination for an overload relay? Type 1 and Type 2 are the two coordination levels defined in IEC 60947-4-1 for a motor starter after a short circuit passes through it — Type 1 allows the contactor and overload relay to be damaged as long as no person is endangered and no fire results, while Type 2 limits the damage to light, easily-separated contact welding so the starter goes back into service without replacing parts. Pick the wrong type for the job and you either pay for an SCPD you did not need, or replace a contactor every time a fault clears. This article covers what the standard actually tests, how to read a manufacturer's coordination table, the let-through energy that decides the outcome, and how to choose between the two for a given panel.
The Three Devices in a Coordinated Starter
A coordinated motor starter is not one product — it's three: the SCPD (fuse or MPCB/circuit breaker) that clears the short-circuit current, the contactor that switches the motor under normal running and starting current, and the overload relay that carries the motor's full-load current continuously and trips on sustained overload. Each device does a different job. The overload relay is not rated to interrupt a short circuit and is not designed to; that current, often tens of kiloamps, passes through the contactor and overload relay on its way to being cleared by the SCPD, and it's this pass-through event that coordination testing addresses. Our thermal overload relay engineering guide covers how the relay itself is built and set; this article picks up where the SCPD, contactor and relay have to work together during a fault.
What IEC 60947-4-1 Actually Tests
Coordination testing answers one question: when a short circuit occurs downstream of the starter, how much of that fault current's energy reaches the contactor and overload relay before the SCPD interrupts it, and what does that energy do to the parts? The standard does not test the overload relay's trip curve here — that's covered separately under IEC 60947-4-1 standards for contactors and motor starters. Coordination testing runs a declared short-circuit current through the exact SCPD, contactor and overload relay combination, then inspects what is left. The manufacturer states a prospective short-circuit current (Icc) for the test, and the declared Type only holds at or below that current.
What we see in the field: installers sometimes assume any breaker rated above the motor's full-load current will do. It will not — the breaker has to be the specific model, frame and trip setting the manufacturer tested, at a prospective current at or above what is actually available at that point in the panel.
Type 1 Coordination: What Gets Damaged
Type 1 sets the bar low: after the fault clears, the contactor and overload relay must not endanger persons and must not cause a fire, but the standard accepts that they may need to be replaced. Contacts can weld shut, the coil can burn out, the overload relay's trip mechanism can be destroyed. A Type 1 starter clears the fault safely, then someone opens the panel and replaces whatever failed. In cost-sensitive OEM equipment where faults are rare and downtime for a replacement is tolerable, Type 1 is a legitimate choice, usually reached with a standard, lower-cost fuse.
Type 2 Coordination: Back in Service After the Fault
Type 2 raises the bar: after the fault, the only damage permitted is light contact welding on the contactor, and it has to separate with a screwdriver or comparable light effort, no other damage, no parts replaced. A Type 2 starter clears a fault, the technician frees any welded contact, and it's back on line the same shift. That's why panel builders default to Type 2 for motor control centers and for single critical drives, where an hour of downtime costs more than the price difference between fuse classes. Reaching Type 2 usually means a faster-clearing SCPD, a current-limiting fuse or an instantaneous-trip motor protection circuit breaker, sized and coordinated specifically with that contactor and overload relay.
Let-Through Energy Decides the Type
The mechanism behind both types is the same: the SCPD does not clear a short circuit instantly. Between fault initiation and current interruption, some amount of energy — I²t, current squared times time — passes through the contactor and overload relay. A fast, current-limiting device lets through less energy; a slower device lets through more. Type 2 requires that let-through energy stay under whatever the contactor and overload relay can absorb without damage beyond light welding. Swap in a slower fuse, or a breaker with a higher instantaneous pickup, and the same contactor/relay pair might only achieve Type 1, or fail coordination altogether.
Formula: Let-Through Energy Coordination Check — Source: IEC 60947-4-1, Type 1/Type 2 short-circuit test
I²tSCPD ≤ I²twithstand
| Symbol | Description | Unit |
|---|---|---|
| I²tSCPD | Let-through energy the fuse or breaker passes during the fault, at the prospective short-circuit current Icc | A²s |
| I²twithstand | Short-circuit withstand energy of the contactor + overload relay combination, verified in the manufacturer's coordination test | A²s |
| Icc | Prospective short-circuit current at the point of installation | kA |
Reading the Manufacturer's Coordination Table
Schneider, ABB and Siemens each publish coordination tables that cross-reference specific fuse or breaker models against specific contactor and overload relay combinations, with the achieved Type and the prospective short-circuit current the combination was tested at. A table entry might read: 32 A TeSys LRD overload relay with an LC1D32 contactor and a specific gG fuse, Type 2 up to a stated Icc. Change the fuse class, and the same row might drop to Type 1 at the same current, or Type 2 at a lower current. ABB's TA-series and Siemens' SIRIUS 3RU2/3RB3 combinations follow the same logic against their own A-line and 3RT2 contactors, each brand's table only covers its own hardware, so a mixed-brand starter has to be verified independently or left uncoordinated. Before pulling a table, confirm which contactor you are pairing the relay with; our guide on how to select the right contactor covers frame and duty selection that feeds directly into which coordination row applies.
This depends on how the table is organized, and it varies by manufacturer. Some list by overload relay setting range, others by contactor size. Read the current at which the Type is declared before comparing two rows: a Type 2 result at 10 kA is not the same claim as Type 2 at 50 kA, and the site's actual prospective fault current has to be at or below the tested value for the declaration to hold.
Choosing Type 1 or Type 2
Start with what a fault costs you. A single critical pump feeding a process line, a conveyor in an MCC with no redundant drive, a compressor that cannot sit idle, these justify Type 2 and the SCPD it takes to get there. A bench-mounted OEM machine with a spare starter kit in the cabinet, or equipment where an hour of downtime is a minor event, does not need it; Type 1 with a standard fuse keeps the bill of materials down. Many specifications default to Type 2 regardless, because it's the safer assumption when the actual duty cycle is unknown at design time, some engineers over-spec for this reason, and it's a defensible choice even where Type 1 would technically pass.
| Criteria | Type 1 | Type 2 | Uncoordinated |
|---|---|---|---|
| Contact welding | Allowed | Light welding only, separable by hand or screwdriver | Unverified |
| Damage to contactor/relay | Permitted, parts may need replacement | None beyond light welding | Unbounded |
| Restart after fault | After inspection and any replacement | Immediate, after freeing any welded contact | Not guaranteed safe |
| Personnel/fire safety | No danger to persons, no fire | No danger to persons, no fire | Not verified by test |
| Typical use | Cost-sensitive OEM panels, tolerable downtime | MCCs, critical single drives, panel builders' default | Not IEC 60947-4-1 compliant |
An uncoordinated starter is not a lesser Type, it is outside the standard's guarantee entirely. See our explanation of how a thermal overload relay works if the trip mechanism itself, rather than its short-circuit coordination, is what you need to confirm.
Frequently Asked Questions
What's the difference between Type 1 and Type 2 coordination for an overload relay?
Type 1 permits damage to the contactor and overload relay after a short circuit, as long as no person is endangered and no fire results; the starter may need parts replaced. Type 2 limits the damage to light contact welding that separates with a screwdriver or light effort, so the starter returns to service after the fault clears.
Which coordination type does my installation need?
Most panel builders and OEMs specify Type 2 because it keeps a starter in service after a fault, which matters in a motor control center or on a single critical drive. Type 1 is acceptable where downtime after a fault is tolerable.
Does the overload relay decide the coordination type, or does the SCPD?
The combination decides it: the same overload relay can reach Type 1 with one SCPD and Type 2 with a faster-clearing one. Manufacturers test specific SCPD, contactor and overload relay combinations and publish the result in a coordination table; substituting any one component invalidates the tested rating.
Can a molded-case circuit breaker replace a fuse and still achieve Type 2?
Yes, provided the breaker, contactor and overload relay combination has been tested and appears in the manufacturer's coordination table at or above the site's prospective short-circuit current. Instantaneous-trip motor protection circuit breakers are commonly used to reach Type 2 because they clear a fault fast enough to limit let-through energy.
What happens if I install a starter with no tested coordination?
The combination is treated as uncoordinated: the short-circuit withstand of the contactor and overload relay is unknown, and a fault can cause damage beyond what either Type would allow, with no verified assurance the enclosure protects personnel. IEC 60947-4-1 compliance requires a declared coordination type, so an untested combination should not go into a compliant panel.
Conclusion
Type 1 and Type 2 are not a spec on the overload relay itself, they are a declared, tested outcome of the exact SCPD, contactor and overload relay combination, verified against a stated prospective short-circuit current. Read the manufacturer's table for that specific trio before assuming either Type applies, check the site's actual fault current against the value the table was tested at, and pick Type 2 where a fault taking equipment offline is expensive. Get any one of the three components wrong and the coordination claim, and the protection it implies, no longer holds.
