Grounding and signal shielding concerns.

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Grounding and signal shielding concerns.

Postby John at the Falls » 13 Jan 2016, 11:36

I attached a photo of my "Tea Cart". It will have 9 axis of various sizes. More power supplies and drivers are on the other side. It is now on wheels so I can move it around to various machines in my shop. I am currently wiring an RJ45 patch panel so I can configure the signal wires for each machine. The high current output from the drivers have a high current terminal strip patch panel separate from the signal wiring.

I am using a twisted pair of CAT5e stranded Ethernet cable for each signal line.

One big question is about tying the power supply case and the driver case to AC ground which is tied to the 110V Neutral line back in the shop circuit breaker box (That is how it works here in the U.S.)

Then I know the computer can be double insulated from the mains (no AC ground, just a 2 prong plug). Then things can get weird with the grounded shield on a USB cable.

All the ground wires of the twisted pairs will be tied to the signal ground on the driver modules or the signal ground on the MK3 board.

Andrej recommends letting the ground shield opposite the driver module float which I would tie to the chassis ground if this were one unified system in one nice big metal box.

My thoughts are:

To tie the milling machine frame and the controller system AC power supplies together for a solid 110 Mains ground.

The DC Negative (DC ground) from the power supplies to the drivers are probably an isolated system. Leave them alone.

The laptop power supply and the plug in 12 Volt power supply for the MK3 board have no Mains ground and are floating. Hopefully the Ethernet cable between the MK3 board and computer are floating.

I would consider the signal grounds separate from the DC Negative and the AC Mains ground. Signal ground should be isolated from AC and DC grounds unless connected internally tin the drivers or MK3 board.
I need to be meticulous about tying all the signal grounds properly to the drivers and MK3 board to prevent EMF interference.

I did Avionics in the Coast Guard for 24 years. Flying Faraday Cages designed to take lighting strikes. I followed standards that engineers designed. Everything was tied together. Unlike the US AC ground system, the generated AC was fully isolated from everything except what it was supposed to be powering.

My whole beef is that here in the U.S. , the grounds are tied to the 110 volt neutral which in my book is a live wire. This works until an ice storm drops a line and crosses wires, then your steel stove and refrigerator become hot. My Range exhaust fan and light will turn on. Kids die jumping into water at marinas where some boater plugs the boat in wrong and the engine and prop shaft become hot through the DC ground connected to the now hot AC ground ....

I will go poking around tomorrow with an ohm meter to see where the AC Ground ends and double insulation begins. Then design a system where the signal wires have no chance of connecting to 110 volts through the AC ground. This is my first time working on a system with extensive opto isolation.

I have plasma cutting in my shop. The High Frequency Start on my TIG welder resets my MP3 player and blinks the solid state ballast in the Fluorescent lights. Does not affect the computer or stereo. The welding station has an extra ground rod, all according to code.

My controller box is wood but a metal box is no fix for a poorly designed wiring system with unshielded wires.
I would appreciate any thoughts on this subject.
CNC Cabinet 150514_003.jpg
CNC Cabinet prior to wiring.
CNC Cabinet 150514_003.jpg (166.29 KiB) Viewed 653 times
John at the Falls
Posts: 5
Joined: 13 Jan 2016, 08:53
Controller: Mk3

Re: Grounding and signal shielding concerns.

Postby Support » 16 Jun 2016, 07:20

Terribly sorry for such late reply.
You still need help with the answers?
Posts: 2571
Joined: 07 Apr 2014, 17:39
Controller: Many controllers

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