The coordination of protective equipment is the art of associating a SCPD (short Circuit Protection Device, such as a fuse or magnetic circuit breaker) together with a contactor and thermal overload relay. The object of this is to interrupt an over-current (1 to 10 times the rate motor current) or short-circuit current)>10 times the rated motor current) in sufficient time to avoid danger to either personnel or the installation.

The prospective short-circuit current is a characteristic of the installation at a given moment. It is calculated by taking onto account the power source, the voltage and line impedances (cables, connectors, transformer, etc.). The coordination test is carried out at a conventional short-circuit current “lq” s defined by the manufacturer of the device (for example 50 kA at 380 V for a motor starter comprising fuses + contactor + thermal overload relay)> The standard introduces a new perspective short-circuit current “lr” according to the AC-3 rated operational current of the device, such that lr < lq (for example: for 63 A, lr = 3 kA). The coordination must always be checked for both lr and lq at the same time.

The IEC 947 standard defines two types of starter, SCPD coordination:

- Type1 (previously type “a” in IEC 292-1)
Upon a short circuit, the equipment must not present a danger to personnel or installations. After disappearance of the short circuit, the device cannot be operated again without repair or replacement of parts.

- Type 2 (previously type “c” in IEC 292-1)
Upon short circuit, the equipment must not present a danger to personnel or installations. After disappearance of the short circuit, the device should not show deterioration or altered settings. Any welded contacts on a contactor must be easily separable. No replacement parts are permitted in the course of the test, except for fuses, which must all be changed.