AB SMC3 Softstart having Shorted SCR

Hi All,
We have about 13Pcs of SMC3 installed which drive about 4 sets of motor each, the total motor load in each Softstart is within the SMC3 rating, the number of start stop for each smc is about 32 per hour, it is within the recomendation graph given by Rockwell, However from time to time we encouter SCR fault from different smc from within the 13 units. we install the filter as recomended by AB but it was not solving the problem, try putting the panel temp to 23deg but failed, I've raise this issue to RA tech but nothing concreate answer was given. remember that if the fault happen we can just push the reset and run again so basically its not a SCR fault. I've been asking this question to RA, When the SCR or at what instance the SCR fault happen. up to now we still having this problem.
if you have similar issue and you resolved it,please post..

Thank you very much..

What does the incomming power look like? I had a problem where we were getting noise on the incomming line causing the scr's to misfire. The utility company found a foundry down the road had a bad cap bank and when they were switching it created the noise. Just a swag?

The incoming power hmmm.. I cannot say totally okay but sometimes i can capture some spikes and sags from time to time but within the limit, the spikes maybe above but the duration is not that much, thats why we put the incoming filter in each SMC to protect the unit from this events. If i install an isolation transformer would resolve this issue? pls help..

thanks you..

If the incomming power is a problem a isolation xfmr would help in my humble opinion, but before I go that extreme, I would hook up a disturbance analyzer to see if the problems with the scrs co-incided with a power probpem.

are you able to check the firing signal for that specific scr and compare it with the same firing signal for the good ones and see if it is still within the allowed range or critical to fault

If the line/load side of the scr's runs very far in the same conduit with other motor leads from the other scr's then the induced voltage in the leads can cause the soft start to trip on a shorted scr. It sees voltage when it should not and assumes a shorted scr's is leaking by. Then it trips setting a fault condition for safety.

RSL