FADAL TRM - Control Cabinet Wiring Advice

[martyscncgarage]

I am about to start wiring a cabinet for a FADAL TRM. It is an open bed mill, it has a 3HP spindle motor. It previously had 22 in-lb servos on X&Y and a 36 in-lb servo on Z (non counterweighted)
Pictures here:

I am refitting it with a Centroid OAK
DMM NEMA 42 1.3KW AC servos (which I realize are overkill for the machine especially in X/Y) but they were more convenient to install as I could reuse couplers and should bolt right on in place of the original FADAL/GLENTEK servos.

My questions are, per the attached "generic" schematic, (and I realize this is a "kitchen sink" schematic) it shows each drive having a separate overcurrent device and a relay to remove power from it.

You will note in the original cabinet, toward the middle bottom, there is only one Estop contactor. From a practical standpoint, is this still desirable and good best practice for a machine of this size? OR can I run one pair of fuses, through one Estop contactor to feed the three drives? (Space for fourth axis drive provided but will not be wired, for future use). Further to size the pair of fuses, I totaled the number of watts for the 3 drives/motors at 3.9KW. Divided that by 240VAC and come up with 16.25A assuming full wattage. I had planned on using a pair of 15A fuses for the 3 drives.

Could I assume that if I wanted 750W from X/Y and 1.3KW from Z, 750+750+1300=2800W divided by the voltage 240=11.66A I realize I can not control what each motor will draw, any one motor can draw its full potential limited by the drive (this might be a good reason to have separate overcurrent for each motor). I tend to be old school and use cartridge fuses because they react more quickly than a typical general class circuit breaker. I am open to thoughts on this as well. (There are different classes of circuit breakers, HACR being the quickest and generally rated for motor loads)

Right now, the panel is not wired, and there is plenty of room to make changes.

Also, I think for an open machine like this. Max rapids should be held to between 100-200ipm, would you agree with this?

So for the sake of discussion, and good practice, if this were your build, "What would you do?"
Thanks,
Marty

[slodat]

I’m doing the same ish install, except Acorn. I do this type of stuff, in an industrial environment at my day job. We talked about it at work and this is what I’m doing. The T01 DYN4 full load current is ~15a.

Incoming 240vac motor power -> 45a line reactor -> 100a contactor (I used this size because I got a good deal on eBay) -> 50a fast trip curve two pole breaker -> 45a Schaffner EMC Inc. / FN2410-45-33 filter -> 50a DIN terminal block -> drive motor supply inputs. ie: one supply for all three drives vs. DMM’s suggested individual over current protection and contactor.

I do leave logic power on the DYN4 when the e-stop contactor opens (switched and over current protection is separate) so that I can see what caused a drive fault. I am running separate input filters on each drives logic power input.

Electrically, I nor my peer reviewers can see any reason to have separate DYN4 incoming motor supply e-stop and over current. I did this on my last DYN4 machine as well.

I’m typing this on my phone. Sorry for no drawing.

My Tree mill was 250ipm rapid from the factory. It did come with 40lb-in motors.

My .02

[cncsnw]

For small drives like this, I would use a single overcurrent device (set of fuses, or circuit breaker) and a single interrupting contactor. While it is sometimes convenient to be able to isolate individual drives, it is not critical.

One reason for separating them can be to keep the wire size smaller. The overcurrent device has to be sufficient to protect the wire: you cannot use a 50A circuit breaker, then run 14ga wire to the loads.

If you use NFPA79 for guidance, you need to derate (oversize) wiring to motor controllers, servo drives and variable-speed drives, by 25%. So for a 16A motor load, you would need to wire for 20A (12ga). The overcurrent device could be anywhere from 16A to 20A. If you go over 20A, then you need to increase the wire size further.

[martyscncgarage]

For small drives like this, I would use a single overcurrent device (set of fuses, or circuit breaker) and a single interrupting contactor. While it is sometimes convenient to be able to isolate individual drives, it is not critical.

One reason for separating them can be to keep the wire size smaller. The overcurrent device has to be sufficient to protect the wire: you cannot use a 50A circuit breaker, then run 14ga wire to the loads.

If you use NFPA79 for guidance, you need to derate (oversize) wiring to motor controllers, servo drives and variable-speed drives, by 25%. So for a 16A motor load, you would need to wire for 20A (12ga). The overcurrent device could be anywhere from 16A to 20A. If you go over 20A, then you need to increase the wire size further.

Thanks Marc. Is my estimation of the current to the drives reasonable or flawed?
You make good point that fuses are sized for the load, wire must be sized for the fuses used. Excellent point about oversizing the wire for motor controlled loads. So fuses are 15A, for the spindle motor which draws 8A. Would you size the fuses at 10Amps with time delay fuses? OR 15Amp time delay fuses?

At 10Amps it would be permissible to wire the motor with #14THHN coppper wire. At 15Amps, it would be permissible to wire the motor with #12THHN Copper wire correct?

Likewise if the 3 drives are wired to one pair of 15Amp fuses, then EACH drive needs to be fed with #12 wire would you agree?

Thanks for chiming in.
Marty

[slodat]

One reason for separating them can be to keep the wire size smaller. The overcurrent device has to be sufficient to protect the wire: you cannot use a 50A circuit breaker, then run 14ga wire to the loads.

Good point. Thank you!

[cncsnw]

Is my estimation of the current to the drives reasonable or flawed?

Probably in the right ballpark, but it would be better to use rated input current values supplied by the manufacturer. Those can sometimes be hard to find, if the manufacturer did not see fit to print it directly on the placard on the side of the drive.

I do see that DMM has a smaller assortment of drives than Yaskawa, using each drive size to run two or three different size motors. Given that, it would be reasonable to scale the rated input current from the drive placard down in proportion, if you are using motors smaller than the largest ones the drive will support.

[martyscncgarage]

Here is the lable from the side of the DYN4. Clearly it covers a wide range of drives.
Using Ohm's law, 1300watts/230VAC=5.6A full power.
VERY unlikely ALL 3 drives will pull their full power. Hence my suggestion that 15Amp fuses should be good for this application and very unlikely that a bed mill like this will use 1.3KW of power on X/Y. Worst case the fuses blow as they should, is my thought.

Marty

[slodat]

I feel the same way, Marty. I've presented this to two control engineers at the day job. The whole "follow manufacturer's recommendation" thing leaves the conversation clear as mud. I ordered individual circuit breakers for each drive and am sizing the wire appropriately. I'm in a rural area and I have to order everything online. I get tired of waiting for stuff to arrive, and that often is a driving force in my decisions. The same thing comes up when sizing supply for VFD's when powering from single phase.

[martyscncgarage]

I feel the same way, Marty. I've presented this to two control engineers at the day job. The whole "follow manufacturer's recommendation" thing leaves the conversation clear as mud. I ordered individual circuit breakers for each drive and am sizing the wire appropriately. I'm in a rural area and I have to order everything online. I get tired of waiting for stuff to arrive, and that often is a driving force in my decisions. The same thing comes up when sizing supply for VFD's when powering from single phase.

I think the fuses/overcurrent should be sized to the MOTOR wattage, not the MAX capacity of the drive. The electrician in me says you are protecting the motor. Ohm's law prevails generally.

This is why I thought this makes for good discussion.

Marty

[slodat]

I started my career as an electrician, been a high voltage relay and controls craftsman for the last 12 years. Just got the on site machine shops big cnc equipment in our fold at the day job. I’m with you. Completely. DMM specifying a 30a breaker in a 15fla drive on a motor load that won’t exceed 10a for more than a handful of cycles seems.. silly to me. Most of the motor load is going to be a fraction of that 5-6a fla. I asked them about this and the response was the same drawing I’m sure you have showing 30a breaker and contactor per drive. Clear as mud

I went with 10a breaker per drive, 14ga cable.