Single phase motor protection?

[PreLC]

Hi PLCs.net!

I'm working on a multi-motor system, most motors are single phase, driven by servo drives.
I wanted to check what kind of motor protection is available upstream of drives? Currently I'm speccing slow response fuses with indicators which will go to the PLC.

 

[OkiePC]

I've never seen a single phase servo motor. I have seen some AC and DC servo motors that are powered by drives supplied with single phase. In those cases, I refer to the mfg literature for branch circuit protection recommendations.

 

[I_Automation]

For single phase motors I (first encountered, then started) use a 3 pole Motor Overload.


Run the HOT lead through OLR T1 then loop up and through OLR T2, run the neutral wire through OLR T3.

 

[PreLC]

powered by drives supplied with single phase. In those cases, I refer to the mfg literature for branch circuit protection recommendations.

This is the case, motors are not going to receive AC Sine waves.

Thanks, will lookup branch circuit protections as options from the manual.

 

[PreLC]

For single phase motors I (first encountered, then started) use a 3 pole Motor Overload.

Is there any documentation/citation behind this approach? I also found this circuitry on the internet, but is this reasonably safe to do?

 

[Zimmer]

Is there any documentation/citation behind this approach? I also found this circuitry on the internet, but is this reasonably safe to do?

Know nothing about your application, but connecting a standard single phase motor, with a 3 phase OL as described above is perfectly safe, obviously with the overload set for the FLC of the motor.

Re. documentation, first hit, I got on google seems to be from a Schneider dude

https://www.se.com/eg/en/faqs/FA228044/



.

 

[PreLC]

Know nothing about your application, but connecting a standard single phase motor, with a 3 phase OL as described above is perfectly safe, obviously with the overload set for the FLC of the motor.

Re. documentation, first hit, I got on google seems to be from a Schneider dude

https://www.se.com/eg/en/faqs/FA228044/



.

Great to know!
I didn't realize that was from Schneider directly. Good enough for me, thanks!

 

[goghie]

If motors are driven with servo drives, you do not need to protect motors, you need to protect drives. Drives will protect motors.

 

[JesperMP]

If motors are driven with servo drives, you do not need to protect motors, you need to protect drives. Drives will protect motors.

Agreed.
The documentation for the servo drive must specify the protection that is to be installed before the drive.

 

[PreLC]

Agreed.
The documentation for the servo drive must specify the protection that is to be installed before the drive.

If motors are driven with servo drives, you do not need to protect motors, you need to protect drives. Drives will protect motors.

Agreed with both. Original intent was to ask this(Indicated by "Upstream of the drive"), ended up using placeholder "Motor Protector" as I was looking into MPCB.

Speaking of drive protection, why don't these come as options for the drive? As in - a replaceable breaker that is in the drive's form factor?

 

[I_Automation]

Agreed with both. Original intent was to ask this(Indicated by "Upstream of the drive"), ended up using placeholder "Motor Protector" as I was looking into MPCB.

I actually lost a job at an interview during the CAD test. Their guy came in with a 30 page schematic and had me point out every component on it.


He had a Motor Overload BEFORE a VFD and I pointed out that the M-OLR was rated for the motor FLA, but that's what the VFD puts OUT and can pull significantly more in supplying that output AND charging the DC buss at the same time - That it needed to be a MCB not a M-OLR, the M-OLR could be used AFTER the VFD as a redundancy (they have electronic OLR's built into them)


He got upset he got corrected and I didn't get the job. Guess that's a good thing as the shop closed about a year later, plus it would have been a long daily drive.

 

[goghie]

Speaking of drive protection, why don't these come as options for the drive? As in - a replaceable breaker that is in the drive's form factor?

Don't know. Maybe you should offer to some producer

However I can imagine lot of drawbacks with integrated solution. MCBs, MPCB, are modular. Different regulative require different protection type. Additional cost in certificates. etc