Which thickness CY cable do I need for 1.5kW spindle?

[A_Camera]

Common sense at last

Whatever rocks your boat...

To me, the common sense is NOT to use such thin wires for this purpose. It works, but it is AGAINST common sense.

[Lee Roberts]

Whatever rocks your boat...

To me, the common sense is NOT to use such thin wires for this purpose. It works, but it is AGAINST common sense.

I personally work to the formula: "Nothing Built Strong, Ever Broke"

Following that seems to have worked for me all these years so I know what your saying :-).

.Me

[Doddy]

Not replying to any single post here:

Considering only resistance (okay, a motor is largely inductive - it makes the maths slightly trickier, but there is a significant resistive element to the motor and the basic premise remains)

Simply, given the same conductor type, 0.75mm2 cable has a higher resistance per unit length than 1.5mm2. Similarly, 1.5mm2 has a higher resistance per unit length than 2.5mm2. That fact is irrefutable.

The power dissipated in the cable run is proportional to the resistance.

Also, the voltage drop across a cable run is proportional to the resistance. The higher the resistance, the greater the voltage drop across the cable run.

The voltage drop across the cable run is proportional to the square of the current drawn. So, under load, with greater current draw, the voltage drop across the cable run increases at the square-law of the current, and implicitly, the load.

The voltage at the spindle is the terminal voltage of the VFD, minus the voltage drop across the cable run.

The mechanical power provided by the spindle is proportional to the terminal voltage of the VFD.

So, the lower the CSA of the cable run, the lower the voltage at the spindle. This drop increases as the load increases. This impacts directly the available power of the spindle. Cable CSA is related to performance.

Of course, the standard cable ratings easily found on the interweb don't consider the performance of the spindle, only the safe operating mode of the cable under domestic and industrial applications - given the heating effect of the dissipated energy on the cable, and - importantly - the longevity and integrity of the insulation. You might find that a particular cable works, but that the insulation fails after prolonged use.

The spindle manufacturer will provide a design specification for the spindle. This /should/ (I have to provide that caveat for our illustrious Chinese manufacturers who are not unknown to put anything that sounds good in the manual without reference to reality) allow the spindle to operate as designed. It is not unreasonable to expect then, that if you compromise that design, you'll compromise the performance of the spindle.

Finally (I need to get back to the bottle of wine), don't design a system assuming any strands on a multistranded cable will fracture - at that point the mechanical design of the system has already failed and catastrophic failure of the cable will occur in short time.


An analogy. If an architect specified a 152x89 RSJ. Would you chose to replace this with a 127x76 RSJ that you had lying around? It might well work, the building would probably stay upright after you've finished it. Hey!, the architect is clearly a fool.

[lucan07]

I might be a bit fick but did you just say "Fatter cable will make spindle go faster"?

[JoeHarris]

An analogy. If an architect specified a 152x89 RSJ. Would you chose to replace this with a 127x76 RSJ that you had lying around? It might well work, the building would probably stay upright after you've finished it. Hey!, the architect is clearly a fool.

Not wishing to fuel the fire, but what cross section cy are people generally using between driver and stepper?! (genuine question!)
Signed foolish architect

ps. This video is quite useful for those with less experience when it comes to connecting steppers to the cable itself, I would be interested to hear comments on his methodology from those who have done this many times before... - https://www.youtube.com/watch?v=Xbiipb6nnZg

[A_Camera]

6A for Control Signals.!!!!!. .

Don't worry Bee it will be fine. These spindles at full load only pull 8A. In practise and while heavy cutting they actually rarely pull above 5A. 0.75mm2 is rated 6A and this is very conservative rating. Again in practice and for the very rare occassions you do pull full load of spindle/VFD it will easily allow to pull 8-10A without any trouble. In case of Short Circuit the VFD it's self will protect you with it's Max current setting and then you have the Fuse.

You can't ONLY go only after currents, if that was all that mattered we could use hair thin wires for all type of communications. You are blindly staring at one parameter only.

Generally speaking, yes, 0.75mm2 is enough for most cases for the spindle, but why use something as thin as that if 1.5mm2 is safer, stronger, not much heavier, better suited for the purpose and hardly much more expensive. Can you come up with ONE good reason other than most people don't continually use up more than 5A?

I chose 0,75mm2 for the control signals because that is what I have, apart from 1.5mm2 and FTP CAT6 cables (0.5mm2), so I chose the 0.75mm2. The FTP cable would be good as well, but I like the Ölflex cable more, it is easier to handle for the purpose.

[JAZZCNC]

Generally speaking, yes, 0.75mm2 is enough for most cases for the spindle, but why use something as thin as that if 1.5mm2 is safer, stronger, not much heavier, better suited for the purpose and hardly much more expensive. Can you come up with ONE good reason other than most people don't continually use up more than 5A?

I could but won't get into slanging match with someone so narrow minded. I'm also not saying I would have used 0.75mm2 because I wouldn't have. However only because I have 1.0mm2 & 1.5mm2 which use all the time. If I'd only had 0.75mm would have used it.

The point of my first post was more to re-assure the OP "Bee" that his choice, which he'd already purchased before you posted would be fine. This by now he surely knows because some Muppet started up the thread again 3 mth's after he posted.!!

[A_Camera]

I could but won't get into slanging match with someone so narrow minded. I'm also not saying I would have used 0.75mm2 because I wouldn't have. However only because I have 1.0mm2 & 1.5mm2 which use all the time. If I'd only had 0.75mm would have used it.

The point of my first post was more to re-assure the OP "Bee" that his choice, which he'd already purchased before you posted would be fine. This by now he surely knows because some Muppet started up the thread again 3 mth's after he posted.!!

OK, so you would not use 0.75mm2, just want to comfort someone who bought the cable... well, the reason for the Muppet to start up the thread LESS than 2 mnts after Bees last post was to try to open the minds of those who are not sure, so they just follow the stream and go after the majority on these forums. I think that can hardly be called narrow minded, more like an effort to help. Considering the costs of the cable, and compared to the price of the CNC the "use what I have available" principle is really very narrow minded and wrong. Apparently you are more keen on name calling than admitting that I was right, there are ONLY advantages of a stronger, better cable, no disadvantages. You don't answer my question because there is just one answer. Anyway, at least in this post, you made it clear that the 0.75mm2 would have not been your choice, so basically, we actually agree.

...and in all honesty, if you really know what I think you know, then I don't think you would have used 0.75mm2 cable if that was all you had at home. I think you would have done the same I would have done, ordered 1.5mm2 and possibly used the thinner one until the better one arrives...

Like I said, what works and what is right are not necessarily the same.

[JAZZCNC]

Apparently you are more keen on name calling than admitting that I was right, there are ONLY advantages of a stronger, better cable, no disadvantages. You don't answer my question because there is just one answer. Anyway, at least in this post, you made it clear that the 0.75mm2 would have not been your choice, so basically, we actually agree.

I wasn't name calling more stating the obvious. IMO it's muppet with over active Ego that posts reply to question which had been answered already and acted upon by the OP months ago.!
I don't doubt your knowledge of electricker and in principle Yes your correct so if your Ego needs a massage I'll glady ablige and say I agree that 0.75mm shouldn't be first choice.
However the fact still remains 0.75mm2 would and will work perfectly fine. All your arguments regards Cable strength, ridgidty etc are mute because it's stupid thing to rely on cable for strength when it should be supported with bracket. The Only thing that matters is if cable can handle the load of the device it's powering while in prolonged use and clearly it can.

...and in all honesty, if you really know what I think you know, then I don't think you would have used 0.75mm2 cable if that was all you had at home. I think you would have done the same I would have done, ordered 1.5mm2 and possibly used the thinner one until the better one arrives...

Why would you presume to predict what I would do.? . . . I don't know me so you or anyone else stands NO chance predicting my actions.!!
If I'd took the time effort to fit it then I'd consider it safe and it would stay on. The ONLY time I might do this is in emergency situation to get machine up and running.

Like I said, what works and what is right are not necessarily the same.

This is contradiction.!! . . . . . If it's working Correctly then it's Right.!!

[lucan07]

This is contradiction.!! . . . . . If it's working Correctly then it's Right.!!

Glad to hear it JAZZ I was almost ready to swap out the 6560 on the Sieg conversion but now you say its right I will leave it where it is!