Star/Delta

Stephen,

I think you are probably looking at it from the wrong point of view. You are not replacing a "star/delta" contactor but rather you are replacing two contactors (or possibly three contactors) which are connected to form a star/delta starter. The interlocking is set up through the auxiliary connections. You don't need to replace all contactors just because they are interlocked but you do need to ensure that the interlocking and connections of the replacement(s) are correct for the function. However if one has failed it may be best to replace all the contactors in the starter at the same time.

You need to know the operating coil voltages, the main contactor voltage (phase-phase and phase-earth) and the rated current. You will generally also need to know the making current capability (i.e. if the contactor closes onto a short circuit, that it can carry the fault current until such a time as the protective device interrupts that current). If in doubt, the safest option may be to replace the failed contactor(s) with the same make/model/rating.

Alasdair

That makes sense. Thanks for your help!

Don’t forget that some Y/D pairs may be mechanically interlocked in addition to the electrical interlocking.