Line Loss C ?

Hi all,

I am using a AB SMCflex soft starter for a 50HP motor on a bandsaw.
Sometimes when starting the motor it faults. The fault occurs as the motor is ramping up.

The fault is #43 Line Loss C

It seems that when the infeed to the saw (belt and pressroll driven by PowerFlex 40 VFD) this fault is more common.

I am really at a loss to as why this is happening, the manual says to just check the wiring and go from there. The electrician checked the wiring for the motor and it seems fine.

any help would be appreciated.

A few years back we installed 4 SMC-2 Soft starters on 4 projects at one location. ALL of the starters would fault intermitently with no known cause. Eventually after a lot of head scratching and trouble shooting, we replaced them with a differant brand. The problem was resolved...

It wouldn't be very lightly loaded on startup would it?

Have you monitored each leg of your incoming power?

Slightly O/T, due to arc hazard requirements, our customer have been changing their main disconnects from circuit breakers to fuses so I was concerned about short-phasing our motors (75-250hp) and power supplies. I've started adding A-B 813E-s Phase Monitors (about $180 US) to condition the control signals of all 3-phase devices hoping that it will provide an additional level of protection. I guess it could be argued its not required but I've seen some bad things happen when the legs get unbalanced, especially to servo systems.

Allen Bradley SMC-Flex Ser. B User's Guide said:

Line Loss F41, F42, F43

During expected SCR gate periods, the power pole voltage and currents are monitored. If the SCR conduction is discontinuous, a fault is indicated.

Possible Causes:
* Line Distortion
* High impedance connection

Possible Solutions:
* Check supply voltage for capability to start/stop motor
* Check for loose connections on line side or motor side of power wires

Click to expand...

valley_brent said:

It seems that when the infeed to the saw (belt and pressroll driven by PowerFlex 40 VFD) this fault is more common.

Click to expand...

What exactly are you trying to say about the infeed? If you were saying that the fault was happening when the infeed was also starting, then my first guess would be that the infeed was causing a voltage drop during startup that in turn causes your soft start to fault.

Did your electrician just check the connections or did he do anything to test the resistance or impedance of the wiring? From what I understand a high impedance connection can also be caused by damaged or overheated wiring in addition to a loose connection.

I'll be the first to admit that I'm no expert on the subject, but without being there that's my shootin' from the hip guess.

monkeyhead said:

Did your electrician just check the connections or did he do anything to test the resistance or impedance of the wiring?

Click to expand...

Kind of what I am thinking as well... I think you are seeing a large enough voltage drop on one line during start up to fault the SMC.

The fault seemed to be thrown when the infeed was already running.

the bandsaw motor is under very little load when starting, since we dont start it with a piece of lumber in the blade

im guessing that maybe the softstarter may be a little too sensitive to a voltage drop that may be occur from another load. but the voltage drop shouldnt be isolated to one line...

there are going to be some more configuration changes tomorrow, so perhaps the problem will disappear....

There could be a problem with your SMCs for this application. 50hp under little or no load could trip. Call Rockwell's Drive Support and let us know what they say

I think your softstarter is faulting due to high frequency harmonics in the power supply. These are often made worse by nearby AC drives. Since you seem to indicate that the fault is occasionally seen when the infeed drive is NOT running, that would indicate dirty power even without the inverter.

Most softstarters are pretty tolerant of dirty power but, possibly, the AB unit is not. I would buy a set of 3% line reactors for the input leads on the softstarter. These would be rated for the 50hp current and would provide some high frequency filtering for the power regardless of where it was coming from.

You shouldn't have to do it but it seems necessary in this case.

Contact Tech Support and specifically ask about the fix for this. It is not documented because the circumstances need to be properly evaluated before being applied.

monkeyhead said:

What exactly are you trying to say about the infeed? If you were saying that the fault was happening when the infeed was also starting, then my first guess would be that the infeed was causing a voltage drop during startup that in turn causes your soft start to fault.

Did your electrician just check the connections or did he do anything to test the resistance or impedance of the wiring? From what I understand a high impedance connection can also be caused by damaged or overheated wiring in addition to a loose connection.

I'll be the first to admit that I'm no expert on the subject, but without being there that's my shootin' from the hip guess.

Click to expand...

I see this is a very old thread, but we have a 400V / 55kW motor mounted on a gearbox on a ingredient mixer. System was converted from star/delta to SMCFlex. We have been experiencing line loss C faults on and off for a very long time. Intermittently. We have replaced the complete SMC a number of times, fault goes away and then appear weeks or months later again. We have replaced only the control module, same result, but always short lived. Yesterday we had the same line loss fault and replaced the SMC, still line loss fault. We have checked every connection in the panel with no luck. Read the post about the the motor connections and opened up the motor terminal box. Found that one of the studs had been replaced with a bolt and the motor cable had been terminated with a lug from underneath. The lug had signs of corrosion and the cable end was in bad shape. Re-terminated the cable and for the past 18 hours we have not had a single fault. Still early days (hours), but looks like it could have been the motor termination(s) in our case that has been giving us this fault. Thank you for the info provided, it certainly helped us.