Question on contactor

[bret]

Just curiosity in the area of longevity and reliability of the continuous duty relay, looking at the amp rating for the CD relay I see 100-200 amps, on the starter relay I see 400-600 amps. The starter current of 300-400 amps passes through both. Is the current rating only for the contacts closing current, or the holding current? it looks like the materials are the same except for the primary coil windings and return springs.....

 

[rapid_ascent]

Bret,

Interesting observation. I would guess that it has to do with the current at the time of switch closure. The main contactor contacts will be already be closed at the time the starter contactor is being enabled. The rating of a closed switch is probably based upon average current not peak since it is primarily a thermal rating. The starter contactor on the other hand has to be able to handle the peak surge currents while the contactor switch is switching. Just a guess on my part since this us a little out of my area of expertise.