Allen bradley SMC flex no load trip fault#40

[Firoj_aga]

Motor running for 2 hours, when load is reduced then it is tripping in no load.
We want to run the motor irrespective of loading condition.
Kindly suggest for the same

Fault 40: no load tripping.


Hence how to avoid no load fault

 

[PLCnovice61]

What model/size drive, what amps motor and type of load?
Is this a new install or existing?

 

[Firoj_aga]

Smc flex 150
motor flc: 360amps

sometimes it runs 4 hr.
But whenever loading is reduced to minimum it trips in no load

we want to run it without load also

 

[jraef]

What that fault really means is that there is >25V votlage drop across the SCRs during starting (or soft stopping). It's the result of a pre-start check, so you will not get this fault if the motor is running / coasting because the bypass contacts will be closed.

So the usual cause is that something is opening and re-closing your start / run command, which tells the starter to re-start, but because the motor is regenerating there is a greater voltage difference across the SCRs. So the first thing to check is actually your control system, as in something is "bouncing" or chattering. A voltage fluctuation >15% in your control power will do it too.

If you have anything on the load side, such as a load isolation contactor or a 2 speed contactor setup, that contactor opening and closing will do it too.

If you have an external bypass contactor, not just the internal one, you need to have programmed the starter to tell it that, otherwise that might cause this too. But I'm pretty sure it would do it all the time, not just sometimes. Sometimes is usually a clue that it's a control circuit issue.