Concerning these Cutler-Hammer motor starters for supply/exhaust air fans - I looked at three starters including the one that we replaced the transformer in. I checked the VA, current on the secondary of the transformer, fuse size on the secondary and checked operating temp with a FLIR IR scanner.
The current on the secondary was 0.4 amps for the two comparison starters and 1 amp on the starter with the new transformer (I measured 1.8 amps prior but that was on the load side of the fuse - need to double check that).
The fuse size varied from 2A-3A @ 250V.
The transformer size varied from 100VA to 125VA.
The operating temp for the new 100VA transformer that I put in a week ago was 50 degrees Celcius. in one of the comparison starters there was an identical 100VA transformer, age unknown, that measured 82 degrees Celcius (plus I noticed that some of the various conductors insulation was cracked to the point you could see the copper showing through). The third control transformer was the 125VA and it had temp of 75 degrees Celcius.
After a little research I now understand that these starters are mid 70's vintage. I am suggesting that we start going through all of these starters and do some upgrading hopefully before another one fails.
