Standard Cabling Procedures

[PEU]

Hi, Im assembling the controller box of my CNC router and a very basic question came to mind. I started browsing this section for threads about cabling but found nothing.

So my questions are:

What is the best way to route cables inside the control box to avoid interferences?

Routing power to drivers? daisychaining or path for every one?

Where to use shielded cable?

Thanks in advance


Pablo

[Evodyne]

Hi,

A few things, there are probably more. High AC voltages or large current PWM DC signals will be the biggest source of problems. In industrial cabinets, we always keep the AC and low voltage apart. This would apply to the motor drive wires too. If AC/motor leads must cross other wiring, the conductors should be at right angles-they should cross at 90 degrees. Don't coil up excess wire-take the time to dress it up neatly. Have you communications cabling enter the box away from the AC and motor leads. Don't daisychain!!! Have a common ground point and run individual conductors to the drives. Fuse the drives and the supply properly. Don't be afraid to use bypass capacitors liberally: little 0.1 uF ceramics in parallel with 470 uF electrolytics work well. Use these ahead of your different devices - drivers, any breakout hardware, etc. Make sure your wiring that might handle higher currents is of a sufficient gage. Encoder wiring (sorry, steppers or servos-I don't know which you are using) is often shielded. You never want to have the shield connected to the devices at both ends-this can invite gound loops. You can use a meter to see if there is continuity between the motor and the encoder shield. If so, don't ground the shield at the controller. If not, then ground the shield to the common panel ground point. There's probably more, but it's early and I need to go get some coffee. Good luck!

Sincerely,

Lance

[jderou]

what is the reason for the bypass capacitors?

[Evodyne]

Originally Posted by jderou what is the reason for the bypass capacitors?

Capacitors in general act as short circuits to AC. In a box where a lot of noise exists you want to shunt the current from the noise (which will be AC) around devices instead of it having it pass through them and influence the electronics. If you buy the older Geckos-the G201 & G210, you are asked to install the 470 uF at the drive if the power leads are of any length. The newer models have the caps in them-you can see the ends of them in the pictures. The two capacitors act on different frequency ranges, so using both is more complete shunting.

Lance

[PEU]

twisting the power cables like braids help? Took the idea of network cabling, but not sure if it applies to AC


Pablo

[Al_The_Man]

Twisting cables, both AC and DC help cancel magnetic field effects produced by the curents in the cable, especially high energy ones.
Al.

[PEU]

Now for the outside part of the cabinet, for each axis I have 4 wires that go to the motor and another 2 that go to the limit switches, what is the best way? sending all 6 wires together in a multipair cable or motor and switches apart?

And for motor all 4 wires in a single multipair or 2 cables: step/dir and +/- ?

Thanks


Pablo