MCB to turn AC motors on and off.

[Deltaforce]

Overload relays are not standalone branch circuit OCPD.

The OP refers to individual disconnects but does not say if they contain OCPD. Based on the supplied information it appears the QO breaker is the OCPD for both motors.

Kind state is it violation of 430 or not

 

[Deltaforce]

Make setup of code compliant, i proceed following:
430.24
Largest motor flc 9a of 10 hp motor
Other motor flc5a of 3hp
Feeder ocpd 1.25*9a+1.00*5a=16.25a
Next size feeder ocpd=20a
I think 20a mcb upstream for two motors with overload relays of op ok

 

[Deltaforce]

Assuming op know this, he provided 30a not 20a though, maybe Qo tripping at 20a, mpcb type breaker 20a suitable and code compliant i think

 

[Deltaforce]

In another scenario
30a mcb as branch protect two motors, 430.52 permit 2.5 factor
2.5*9+5=27.5A
So 30a mcb of op ok!

 

[grotor]

Message from OP:
After I had gotten the control circuit wiring diagram from the manufacturer, I discovered that the rocker switch on the control panel should deenergize motor starters for all motors. It was either miswired from the get-go, or someone connected the wires to the wrong terminals later.
Thanks to everyone for your time and expertise. I have definitely learned something new.